Effect of spin-labeled maleimide on 14S and 30S dyneins in solution and on demembranated ciliary axonemes.

The effects of N-1-oxyl-2,2,6,6-tetramethyl-4-piperidinyl)maleimide(SLM) on the pellet height response and ATPase activity of glycerinated Triton X-100 extracted cilia of Tetrahymena pyriformis have been studied. Preincubation of cilia with SLM caused complete inhibition of the pellet height response and an initial increase in ATPase activity followed upon longer exposure to SLM by inhibition of ATPase. The effect of SLM on extracted 30S dynein was the reverse of that for whole cilia: ATPase activity was increased when 30S dynein was added to a mixture of ATP and SLM and inhibited when the 30S dynein was preincubated with SLM. The activity of 14S dynein was only inhibited by SLM. Electron spin resonance spectra of ciliary axonemes that had reacted with SLM for various times showed that much of the covalently bound SLM was strongly immobilized even after 1 min of reaction, when ATPase activity increased twofold. The proportion of strongly immobilized label increased with longer times of reaction. Addition of ATP to SLM-labeled axonemes caused a small decrease in the height of the spectral peak corresponding to strongly immobilized label as compared with that of weakly immobilized label, indicating an increase in rotational freedom of some covalently bound label. The results suggest that ATP causes a conformation change affecting a sulfhydryl group(s) involved in the mechanochemical system. It was also shown that beta,gamma-methylene ATP(AMP-PCP) is an inhibitor of dynein ATPase. This analogue of ATP is not hydrolyzed by whole cilia or by the extracted dyneins and does not cause a pellet height response. With Mg2+ as divalent cation, AMP-PCP inhibits 30S dynein more than it inhibits 14S dynein; with Ca2+, the inhibition of 30S dynein is reduced, and there is no inhibition of 14S dynein. Under conditions where AMP-PCP inhibited 30S dynein ATPase it was much less effective than ATP in protecting against the loss of ATPase activity by SLM. Although SLM inhibited Mg2+-activated 14S and 30S dyneins in solution, it did not inhibit ciliary ATPase activity. These results support the view that at least 2 SH groups are involved in ciliary motility and that their reactivity to SH reagents depends on whether the dyneins are in situ or have been extracted.     

A comparison of the effects of gentle heating,acetone, and the sulfhydryl reagent bis (4-fluoro-3-nitrophenyl) sulfone on the ATPase activity and pellet height response of tetrahymena cilia

Incubation of glycerol-extracted, Triton X-100 demembranated Tetrahymena cilia with 2–10 vol % acetone caused an enhancement of ATPase activity by 2- to 3- fold, depending on concentration and time of incubation. Axonemal ATPase activity was also increased upon incubation with bis (4-fluoro-3-nitrophenyl) sulfone (FNS). Acetone and FNS enhanced the activity of solubilized 30S dynein, but slightly inhibited that of 14S dynein. Heating at 38°C, incubation with FNS, and incubation with acetone activated axonemal ATPase to the same extent. Subsequent studies of (1) the effect of time of preincubation with a spin-labeled maleimide (SLM) at 25°C as a function of pH on the ATPase activity, (2) the concentration dependence of the inhibition of ATPase activity by N-ethylmaleimide or SLM, (3) the ratio of ATPase activity assayed at 25°C to that assayed at 0°C, and (4) the ratio of ATPase activity at pH 8.6 to that at pH 6.9 did not reveal any difference in the properties of the axonemal ATPase after near maximal enhancement by the heat, acetone, or FNS treatments. It was concluded that enhancement of ATPase activity by gentle heat treatment, by incubation with acetone (or other organic solvents), or by FNS results from a conformation change of 30S dynein. The effect of acetone and of FNS on the pellet height response (a measure of the increase in height of the pellet of cilia precipitated by brief centrifugation in the presence of ATP as compared to the absence of ATP) was also determined. Enhancement of ATPase by these reagents did not lead to a decrease in pellet height response. This observation, in conjunction with other data, indicates that there are at least 3 states of the cross-bridge cycle of dynein arms in cilia.     

Effects of sulfhydryl reagents on the ATPase activity of solubilized 14S and 30S dyneins and on whole ciliary axonemes as a function of pH

The effects of five sulfhydryl (SH) reagents – N-ethylmaleimide (NEM), a spin-labeled maleimide (SLM), N-N′-phenylenedimaleimide (PPDM), bis(4-fluoro-3-nitrophenyl)sulfone (FNS), and carboxypyridine disulfide (CPDS) – on glycerol-treated, Triton X-100-demembranated ciliary axonemes of Tetrahymena, on the 30S and 14S dyneins extracted from such axonemes, and on the residual ATPase activity remaining associated with axonemes that have been extracted twice with Tris-EDTA have been examined as a function of pH in the range 6.9–8.6. Preincubation of axonemes and of solubilized 30S dynein with low concentrations of each of the five SH reagents, at 0°C and at 25°C, caused enhancement of the latent ATPase activity. PPDM was the most effective reagent, causing half-maximal enhancement (after 18 h at 0°C) at ～ 0.5 μM, corresponding to 0.19 moles/10⁵ g axonemal protein. The rate constants, k_a, for the enhancement reaction at 0°C depended on whether the 30S dynein was in situ or solubilized; the ratio k_a (in situ) /k_a (solubilized) was > 1 for NEM, ～ 1 for PPDM, and < 1 for FNS. For each SH reagent except CPDS, k_a (at 0°C) increased markedly with increasing pH in the range pH 6.9–8.6; for CPDS k_a increased only about fourfold. At long times of preincubation and high concentrations of NEM, SLM, PPDM, and CPDS, the enhancement of ATPase activity was followed by a loss of activity. The values of k_L, the rate constants for loss of ATPase activity from the peak enhanced level, were much lower than the corresponding values for k_a, and increased with increasing pH. With SLM and PPDM, inhibition continued until the ATPase activity was almost completely inhibited. With NEM, however, the initial rate of loss from the peak enhanced value decreased as the ATPase activity returned toward the control (unmodified) level, and further inhibition was very slow. The differences in degree of inhibition obtained with SLM as compared to NEM suggest that there are at least two classes of inhibitory SH groups on 30S dynein. The ATPase activity of 14S dynein was only inhibited by preincubation with NEM, SLM, PPDM, and, to a lesser extent, CPDS; k_L increased with increasing pH. Preincubation of 14S dynein with FNS yielded conflicting results when the reaction was “stopped” by adding dithiothreitol. When 14S dynein was preincubated at 0 C with FNS and the ATPase activity was then assayed at 25°C, a biphasic pattern of enhancement followed by inhibition was obtained. The residual ATPase activity of twice-extracted axomenes was relatively insensitive to each of the SH reagents studied; an initial rapid loss of some 20–40% of the ATPase activity occurred, followed by a very slow further loss of activity. Increasing the pH increased this slow rate of inhibition. The residual ATPase activity of unmodified twice-extracted axonemes decreased slightly with increasing pH, in contrast to the slight increase observed with increasing pH for the ATPase activity of axonemes and of solubilized 30S and 14S dyneins. The presence of ATP during preincubation of axonemes with PPDM at O°C prevented the enhancement of ATPase activity; only a slow loss of ATPase activity was observed. This rate of loss of ATPase activity was slower than the rate of loss observed (after peak enhancement of activity was reached) when PPDM reacted with axonemes in the absence of ATP. In these properties the SH groups of 30s dynein responsible for the enhancement of latent ATPase activity and for the inhibition of ATPase activity do not resemble the SH1 and SH2 groups of myosin, respectively, since the presence of ATP increases the rates of reaction of SH1 and SH₂ of myosin with SH reagents.     

ATPase activity of Tetrahymena cilia before and after extraction of dynein

Cilia from Tetrahymena pyriformis were extracted twice with Tris-EDTA. The first extraction increased the total ATPase activity by about one-third. No increase in activity occurred as a result of the second extraction, but 40% of the original ATPase activity remained in the pellet. The activity remaining in the pellet differed in its substrate specificity, its thermostability, and its sensitivity to monovalent cation chlorides from the solubilized dynein. Several of the properties of the ATPase activity of whole cilia differed from those computed for a mixture of 40% pellet ATPase + 60% solubilized dynein ATPase. From these differences it was deduced that dynein in situ is more thermostable than is solubilized dynein and, in contrast to solubilized dynein, is slightly inhibited by KCl, NaCl, LiCl, and NH₄Cl. The increase in total activity upon solubilization of the dynein and the changes in thermostability and in sensitivity to monovalent cations indicates that dynein ATPase in situ is modified by interaction with other components of the axonemal bend generating system.The pellet remaining after extraction of dynein by two dialyses against Tris-EDTA was treated with 0.4% Triton X-100 to solubilize ciliary membranes. Less than half of the ATPase activity was solubilized by this treatment. The possibility that the activity remaining in the Tris-EDTA- and Triton X-100-extracted residue represents an additional ATPase of cilia is discussed.     

The roles of noncatalytic ATP binding and ADP binding in the regulation of dynein motile activity in flagella

The regulation of dynein activity to produce microtubule sliding in flagella has not been well understood. To gain more insight into the roles of ATP and ADP in the regulation, we examined the effects of fluorescent ATP analogues and fluorescent ADP analogues on the ATPase activity and motile activity of dynein. 21S dynein purified from the outer arms of sea urchin sperm flagella hydrolyzed BODIPY(R) FL ATP (FL-ATP) at 78% of the rate for ATP hydrolysis. FL-ATP at 0.1-1 mM, however, induced neither microtubule translocation on a dynein-coated glass surface nor sliding disintegration of elastase-treated axonemes. Direct observation of single molecules of the fluorescent analogues showed that both the ATP and ADP analogues were stably bound to dynein over several minutes (dissociation rates = 0.0038-0.0082/s). When microtubule translocation on 21S dynein was induced by ATP, the initial increase of the mean velocity was accelerated by preincubation of the dynein with ADP. Similar increase was also induced by the preincubation with the ADP analogues. Even after preincubation with ADP, FL-ATP did not induce sliding disintegration of elastase-treated axonemes. After preincubation with a nonhydrolyzable ATP analogue, AMPPNP (adenosine 5'-(beta:gamma-imido)triphosphate), however, FL-ATP induced sliding disintegration in approximately 10% of the axonemes. These results indicate that both noncatalytic ATP binding and stable ADP binding, in addition to ATP hydrolysis, are involved in the regulation of the chemo-mechanical transduction in axonemal dynein.     

EFFECT OF SOLUTION COMPOSITION AND PROTEOLYSIS ON THE CONFORMATION OF AXONEMAL COMPONENTS

The effect of solution composition and enzymic proteolysis on axonemes prepared from the sperm of sea urchins, Tripneustes gratilla, has been investigated. Aliquots of axonemes, prepared by treatment of sperm with Triton X-100 and differential centrifugation, were transferred to solutions of different composition with and without intervening tryptic proteolysis, and the particle conformations observed by dark-field and electron microscopy. In most solutions particles in partially digested preparations underwent conformational transformations to coiled or helix-like forms. Proteolysis was accompanied by an increase in the ATPase activity of the digest: by centrifuging down the insoluble digestion products it was shown that digestion resulted in the appearance of ATPase activity in the soluble phase with a concomitant decrease in ATPase activity in the pellet fraction. Gel electrophoresis showed this corresponded to the appearance of dynein in the supernatant and a decrease in dynein associated with the insoluble fraction. Supernatant dynein had a greater specific ATPase activity than dynein extracted from axonemes. Observations on specimens prepared for electron microscopy by thin sectioning allowed a rough correlation to be made between the dark-field observations, chemical analyses, and morphological alterations attendant with the proteolysis and solution conditions. It is concluded that in the intact axoneme the doublet tubules are under considerable tension and that proteolytic destruction of physical restraining elements allows spontaneous conformational alterations of the digestion products. In addition, proteolysis increases the specific ATPase activity of dynein and removes a portion of it from the axonemal structure.     

Activation of sea urchin sperm flagellar dynein ATPase activity by salt-extracted axonemes

When 21S dynein ATPase [EC 3.6.1.3] from sea urchin sperm flagellar axonemes was mixed with the salt-extracted axonemes, the ATPase activity was much higher than the sum of ATPase activities in the two fractions, as reported previously (Gibbons, I.R. & Fronk, E. (1979) J. Biol. Chem. 254, 187-196). This high ATPase level was for the first time demonstrated to be due to the activation of the 21S dynein ATPase activity by the axonemes. The mode of the activation was studied to get an insight into the mechanism of dynein-microtubule interaction. The salt-extracted axonemes caused a 7- to 8-fold activation of the 21S dynein ATPase activity at an axoneme : dynein weight ratio of about 14 : 1. The activation was maximal at a low ionic strength (no KCl) at pH 7.9-8.3. Under these conditions, 21S dynein rebound to the salt-extracted axonemes. The maximal binding ratio of 21S dynein to the axonemes was the same as that observed in the maximal activation of 21S dynein ATPase. The sliding between the outer doublet microtubules in the trypsin-treated 21S dynein-rebound axonemes took place upon the addition of 0.05-0.1 mM ATP in the absence of KCl. During the sliding, the rate of ATP hydrolysis was at the same level as that of the 21S dynein activated by the salt-extracted axonemes. However, it decreased to the level of 21S dynein alone after the sliding. These results suggested that an interaction of the axoneme-rebound 21S dynein with B-subfibers of the adjacent outer doublet microtubules in the axoneme causes the activation of the ATPase activity.     

Effect of thiourea and substituted thioureas on dynein ATPase and on the turbidity response of tetrahymena cilia

The effects of thioura and of several substituted thioureas–phenylthiourea, α-naphtylthiourea, metiamide, and burimamide–on dynein ATPase have been studied. The substituted thioureas are over 30 times more potent than thiourea in causing enhancement of 30S dynein ATPase activity and inhibition of 14S dynein ATPase activity. The effects of thiourea and phenylthiourea can be prevented by very low concentrations of β-mercaptoethanol or dithiotheritol. Axonemal ATPase is also enhanced by the thioureas, but the reaction proceeds more slowly than for solubilized 30S dynein. Enhancement of 30S dynein ATPase by metiamide is prevented by low (～ 1 μM) concentrations of ATP and, less effectively, by AMP-PNP, but not by AMP-PCP even though the latter is a stronger inhibitor of 30S dynein ATPase than is AMP-PNP. The thioureas inhibit the ATP-induced decrease in turbidity (measured as ΔA₃₅₀) of axonemal suspensions. Inhibition of the turbidity response is also prevented by low concentrations of β-mercaptoethanol, but, in contrast to the irreversible enhancement of ATPase activity, inhibition of the turbidity response is largely reversible. The ability of 30S dynein to rebind onto twice extracted axonemes is not changed by treatment with phenylthiourea or metiamide. These observations indicate that the thioureas react with at least two sets of SH or S–S groups on axonemes. Reaction with the group(s) on the 30S dynein causes an apparently irreversible enhancement of ATPase activity. Reaction with another group(s) causes a reversible inhibition of the turbidity response.     

Interrelationships between thermal-, N-ethylmaleimide-, and Ca2+-calmodulin-mediated activation/inactivation of dynein ATPase activities

Interactive effects between calmodulin activation of 30 S dynein ATPase activity and activation by heat or N-ethylmaleimide (NEM) have been studied. Addition of calmodulin during the heat treatment caused a larger increment in ATPase activity (above that caused by heating alone) than did addition of calmodulin after the heat treatment. Similar results were obtained in experiments where activation was caused by NEM treatment. For both the heat and NEM treatments, the synergistic effect of calmodulin when present during the treatment was Ca²⁺ dependent although activation of ATPase activity by either treatment alone was not Ca²⁺ dependent. Heating 14 S dynein inhibited its ATPase activity and reduced the effectiveness of calmodulin as an activator. The activating effect of calmodulin added after heat or NEM treatments was about the same as if the calmodulin was present during the treatment, i.e., interactive effects were minimal. Concentrations of NEM that had little effect on the ATPase activity of 14 S dynein largely eliminated the ability of calmodulin to activate its ATPase activity. Chromatography of the heat-treated 14 S dynein on calmodulin-Sepharose 4B indicated that the loss of sensitivity of 14 S dynein ATPase to calmodulin was not due to loss of ability of the dynein to bind to calmodulin. Retention of calmodulin binding ability was also shown for heat-treated 30 S dynein. These results suggest that calmodulin and heat/NEM activate solubilized 30 S dynein ATPase by separate mechanisms which may include a common process.     

ISOLATION AND REACTIVATION OF THE AXOSTYLE : Evidence for a Dynein-like ATPase in the Axostyle

The contractile axostyle is a ribbon-shaped organelle present in certain species of flagellates found in the hindgut of wood eating insects. This organelle propagates an undulatory wave whose motion, like flagella and cilia, is related to microtubules. Unlike the axoneme of cilia and flagella, however, the axostyle is composed of singlet microtubules linked together in parallel rows. Axostyles were isolated from Cryptocercus gut protozoa with Triton X-100. Normal motility of the isolated axostyle could be restored with adenosine triphosphate (ATP); the specific conditions necessary for this reactivation were essentially identical with those reported for the reactivation of isolated flagella or whole sperm. ATPase activity of the isolated axostyle was comparable to the values reported for ciliary or flagellar axonemes. The axostyle was reasonably specific for ATP. Most of the proteins of the isolated axostyle comigrated with proteins of the ciliary axoneme on sodium dodecyl sulfate (SDS) polyacrylamide gels (i e. equivalent molecular weights). These included the following: the higher molecular weight component of dynein, tubulin, linkage protein (nexin), and various secondary proteins. Evidence for dynein in the axostyle is presented and a model proposed to explain how repeated propagated waves can be generated.     

Binding of 30s dynein with the B-tubule of the outer doublet of axonemes from Tetrahymena pyriformis and adenosine triphosphate-induced dissociation of the complex.

The binding properties of dynein arms to the A- and B-tubules of outer doublets of cilia from Tetrahymena pyriformis were examined, with the following results: 1. When 30s dynein purified from Tetrahymena cilia was added to doublets deficient in dynein arms, it bound to both A- and B-tubules almost equally and formed arms along the edges. The overall length of arms bound to the A-tubule was 22 +/- 3 nm, and that of arms bound to the B-tubule was 24 +/- 3 nm. Each arm bound to the A- and B-tubules was pointed toward the base at angles of 55 degrees +/- 7 degrees and 48 degrees +/- 7 degrees, respectively. In the presence of sufficient amounts of dynein, the arms along the A- and B-tubules were located at intervals of 22.8 +/- 1.5 nm and 22.5 +/- 1.7 nm, respectively. 2. On adding ATP, only the arms bound to the B-tubule were dissociated from the doublet decorated with arms on both sides. The dissociated arms rebound themselves to the B-tubule after hydrolysis of the ATP. When several doublets decorated with arms along both A- and B-tubules were arrayed side by side, the interdoublet spacing increased from 14 +/- 2 nm to 17 +/- 2 nm on addition of ATP. 3. The turbidity of a suspension of trypsin [EC 3.4.21.4]-treated axonemes decreased rapidly on addition of ATP, then recovered partially. Observations by dark-field microscopy and electron microscopy showed that the doublets which had slid out from the axonemes on ATP addition formed large aggregates after hydrolysis of the ATP. The dynein arms were also solubilized from the axonemes upon addition of ATP, and rebound themselves to the B-tubule after hydrolysis of the added ATP. 4. The double-reciprocal plot for the ATPase [EC 3.6.1.3] activity of the trypsin-treated axonemes against ATP concentration was composed of two straight lines, from which the Km values were estimated to be 1.0 and 12.7 micrometer. The dependence of the decrease in turbidity of the axonemal suspension on ATP concentration indicated that the binding of ATP to sites with an apparent dissociation constant of 1 micrometer induced dissociation of the arms from the B-tubule.     

Specific anion effects on ATPase activity, calmodulin sensitivity, and solubilization of dynein ATPases

The basal ATPase activity of 30S dynein, whether obtained by extraction of ciliary axonemes with a high (0.5 M NaCl) or low (1 mM Tris-0.1 mM EDTA) ionic strength buffer is increased by NaCl, NaNO3, and Na acetate, with NaNO3 causing the largest increase. The calmodulin-activated ATPase activity of 30S dynein is also increased by addition of NaCl, NaNO3, or Na acetate, but the effects are less pronounced than on basal activity, so that the calmodulin activation ratio (CAR) decreases to 1.0 as salt concentration increases to 0.2 M. These salts also reduce the CAR of 14S dynein ATPase to 1.0 but by strongly inhibiting the calmodulin-activated ATPase activity and only slightly inhibiting the basal activity. Sodium fluoride differs both quantitatively and qualitatively from the other three salts studied. It inhibits the ATPase activity of both 14S and 30S dyneins at concentrations below 5 mM and, by a stronger inhibition of the calmodulin-activated ATPase activities, reduces the CAR to 1.0. Na acetate does not inhibit axonemal ATPase, nor does it interfere with the drop in turbidity caused by ATP and extracts very little protein from the axonemes. NaCl and, especially, NaNO3, cause a slow decrease in A350 of an axonemal suspension and an inhibition of the turbidity response to ATP. NaF, at concentrations comparable to those that inhibit the ATPase activities of the solubilized dyneins, also inhibits axonemal ATPase activity and the turbidity response. Pretreatment of demembranated axonemes with a buffer containing 0.25 M sodium acetate for 5 min followed by extraction for 5 min with a buffer containing 0.5 M NaCl and resolution of the extracted dynein on a sucrose density gradient generally yields a 30S dynein that is activated by calmodulin in a heterogeneous manner, ie, the "light" 30S dynein ATPase fractions are more activated than the "heavy" 30S dynein fractions. These results demonstrate specific anion effects on the basal and calmodulin-activated dynein ATPase activities, on the extractability of proteins from the axoneme, and on the turbidity response of demembranated axonemes to ATP. They also provide a method that frequently yields 30S dynein fractions with ATPase activities that are activated over twofold by added calmodulin.     

Structural conformation of the ciliary ATPase dynein.

The ATPase dynein forms part of a mechanoohemically active complex responsible for the sliding filament mechanism of ciliary and flagellar motion. Extraction of demembranated cilia from the lamellibranch mollusc Unio or the protozoan Tetrahymena by 0.5 m-KCl solubilizes the outer rows of dynein and, as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, releases the A form (Mr 360,000) of dynein into solution. Negative contrast electron microscopy of the solubilized dynein fraction reveals an homogeneous array of 93 Å particles that we identify as the ATPase dynein in its monomeric form. Because of the method of dynein extraction, the conformation of the molecule, and the size and shape of the outer arms in situ, we suggest that monomeric dynein is only one part of a larger, non-covalently joined molecular complex that forms the entire arm. When KCl-extracted axonemes are viewed by negative contrast but prior to fractionation of the dynein, individual arms can be seen that comprise three to four of the 93 Å subunits, thus suggesting that each arm is a multisubunit polymer of dynein or dynein-like molecules.     

The salt-extractable fraction of dynein from sea urchin sperm flagella: An analysis by gel electrophoresis and by adenosine triphosphatase activity

Previous work has shown that the dynein from axonemes of sea urchin sperm consists of two distinct fractions which differ substantially in their extractability by salt. Upon gel electrophoresis of whole demembranated axonemes solubilized with sodium dodecyl sulfate, the dynein fraction shows two closely spaced bands with apparent molecular weights of 520,000 and 460,000; the proteins in these bands are termed the A and B components of the dynein. Similar electrophoresis of the soluble fraction obtained by extracting the axonemes with 0.5 M NaCl shows a single prominent band containing approximately half of the A component of the dynein (A₁ component). The residue of extracted axonemes contain the other half of the A component of the dynein (A₂ component) and all the B component. Densitometry of the bands indicates that the A₁, A₂ and B components of the dynein are present in approximately equal molar quantity. Electron microscopic studies show that the A₁ component of the dynein constitutes the outer arms on the doublet tubules. Assay of ATPase activity in 0.05 M KCl and l mM ATP indicates about 65% of the total ATPase activity becomes soluble when the A₁ component of the dynein is extracted with salt.     

Interactions of Tetrahymena dynein with microtubule protein. Tubulin-induced stimulation of dynein ATPase activity

The ATPase (EC 3.6.1.3) activity of 30 S dynein from Tetrahymena cilia was remarkably stimulated by porcine brain tubulin at pH 10. The activity increased with increasing concentration of tubulin until the molar ratio of tubulin dimer to 30 S dynein reached approx. 10. The optimum of the ATPase activity of 30 S dynein in the presence of tubulin was 1?2 mM for MgCl₂ and 2 mM for CaCl₂. Increasing ionic strength gradually inhibited the stimulation effects of tubulin. Activation energies of 30 S dynein in the presence and absence of tubulin were almost the same. At the temperatures beyond 25 °C stimulation effects of tubulin disappeared. ATP was a specific substrate even in the presence of tubulin. In kinetic investigations parallel reciprocal plots were observed in a constant ratio of divalent cations to ATP of 2, indicating that tubulin was less tightly bound to 30 S dynein in the presence of ATP than in the absence. The similar results were obtained at pH 8.2. 14 S dynein and the 12 S fragment which have poor ability to recombine with outer fibers were also activated with brain tubulin.     

Isolation of cilia from porcine tracheal epithelium and extraction of dynein arms

Milligram amounts of mammalian ciliary axonemes were isolated from porcine tracheas. These were reactivated upon addition of ATP, indicating intact functional capability with a mean beat frequency at 37 degrees C of 8.2 Hz. Electron microscopy showed typical ultrastructure of the isolated demembranated axonemes. Electrophoresis into polyacrylamide gradient gels containing sodium dodecyl sulfate revealed reproducible protein profiles from ten different tracheal preparations. Four major protein bands were observed in the 300-330 K molecular weight region, as well as tubulin at 51-54K. Extraction of the isolated tracheal axonemes with 0.6M KCl removed the outer dynein arms seen in electron microscopic cross-section of axonemes, preferentially solubilized two of the high molecular weight proteins at 320 and 330 K, and resulted in a three- to four-fold increase in ATPase specific activity. Sedimentation of the dialyzed salt extract on a 5-30% sucrose density gradient and subsequent fractionation yielded two peaks of ATPase activity. The faster migrating, 19S major ATPase peak correlated with the 320 and 330 K proteins, and two other proteins at 81 and 67 K. The slower sedimenting, 12S minor ATPase peak corresponded to a 308 K protein and two smaller proteins at 33 and 48 K. Thus, the outer dynein arm of tracheal cilia appeared to be associated with at least two high molecular weight proteins. These results demonstrate that adequate quantities of functionally intact axonemes can be reproducibly isolated from porcine tracheas, allowing further fractionation and analysis of mammalian cilia.     

The regulation of the rate of ATP hydrolysis by H-meromyosin

The effect of N-ethylmaleimide on the ATPase activity and ADP binding of tryptic H-meromyosin was studied at 6 and 23 °C temperatures. The affinity constant of H-meromyosin for ADP with Mg as activator was increased by small concentrations of N-ethylmaleimide (2.25 moles per mole of enzyme) at both temperatures, accompanied by activation of ATP hydrolysis at 25 °C and inhibition at 6 °C. With higher N-ethylmaleimide concentrations, the ATPase activity was inhibited at both temperatures, without comparable inhibition of ADP binding. Rapid kinetic analysis of the rate of development of difference spectrum after the addition of ATP or ADP to H-meromyosin indicates, that blocking of the S₁ and S₂ SH groups of H-meromyosin decreases both the formation (k₁) and the dissociation (k₂) rate constants of H-meromyosin substrate complex. At 6 °C, in the presence of Mg, the value of k₂ for ADP is similar to the turnover number of ATP hydrolysis, suggesting that dissociation of ADP from the active site may be the rate-limiting step of ATP hydrolysis. At 23 °C, the turnover number of Mg-moderated ATP hydrolysis is much smaller than k₂, indicating that the rate limitation shifted so another, so far unidentified, step.     

Biochemical Analysis of a Mutant Tetrahymena Lacking Outer Dynein Arms

ABSTRACT. Tetrahymena thermophila mutants homozygous for the oad mutation become nonmotile when grown at the restrictive temperature, and axonemes isolated from nonmotile mutants lack approximately 90% of their outer dynein arms. Electrophoretic analyses of axonemes isolated from nonmotile mutants ( oad axonemes) indicate they contain significantly fewer of the 22 S dynein heavy chains that axonemes isolated from wild-type cells (wild-type axonemes) contain. The 22 S dynein heavy chains that remain in axonemes isolated from nonmotile, oad mutants are assembled into 22 S dynein particles that exhibit wild-type levels of ATPase activity. Two-dimensional gel electrophoresis of oad axonemes show that they are deficient in no proteins other than those proteins thought to be components of 22 S dynein. This report is the first formal proof that outer dynein arms in Tetrahymena cilia are composed of 22 S dynein.     

Kinetic properties of dynein ATPase from Tetrahymena pyriformis. The initial phosphate burst of dynein ATPase and its interaction with ATP analogs.

1. Dynein was extracted with 0.5 M KCl from Tetrahymena axonemes. SDS-gel electrophoresis of the extract indicated that about 50% of the extracted protein had a molecular weight of about 3.5 X 10(5), and that 90% of the proteins with this weight had been extracted. 2. The ATPase [EC 3.6.1.3] reaction of the KCl-extracted dynein fraction was enhanced by 60-80% by addition of the outer doublet fraction. It showed an initial burst of Pi liberation of about 1 mol per mol of proteins with a molecular weight of 3.5 X 10(5). 3. We examined the interaction of the dynein-tubulin system from Tetrahymena cilia with ten ATP analogs [2'-dATP, 3'-dATP, epsilonATP, FTP, 8-NH(CH3)-ATP, 8,3'-S-cyclo-ATP, 8-Br-ATP, 8-OCH3-ATP, 8-SCH3-ATP, and AMPPNP]. Among them, 2'-dATP and 3'-dATP were good substrates for dynein ATPase, as they induced the dissociation of dynein arms from the B-tubule of outer doublets, the sliding movement between outer doublets, and the bending movement of axonemes. The other analogs did not induce the dissociation or the sliding movement. 4. Among the ATP analogs tested, only 2'-dATP and 3'-dATP induced the reorientation of cilia on the Triton model of Tetrahymena; the reorientation rates were smaller than that induced by ATP.     

A proposed mechanism for the stimulatory effect of bicarbonate ions on ATP synthesis in isolated chloroplasts

The effect of bicarbonate ions on induction of Mg²⁺-ATPase activity, on the N-ethylmaleimide inhibition of phosphorylation and on energy-dependent adenine nucleotide exchange has been examined with pea seedling chloroplasts. Incubation of chloroplasts with N-ethylmaleimide in the presence of 15 millimolar bicarbonate in the light results in enhanced inhibition of ATP synthesis when the preillumination pH is maintained between 7.0 and 7.5. Bicarbonate also enhances Mg²⁺-ATPase activity when it is included in the light-triggering stage at pH 7.0. The conditions (medium pH, bicarbonate concentration, etc.) for demonstrating the bicarbonate-induced enhancement of the N-ethylmaleimide inhibition and ATPase activity are similar to those required for the direct effect of bicarbonate on phosphorylation. Bicarbonate, under the same conditions, does not affect adenine nucleotide exchange (binding or release). It is concluded that the stimulatory effect of bicarbonate on ATP synthesis may be related to its ability to alter directly the conformation of the chloroplast coupling factor under conditions (suboptimal pH) where the enzyme shows minimal activity.