Activities of 3,4-benzpyrene hydroxylase systems reconstituted by means of self-assembly from control and 3-methylcholanthrene-induced liver microsomes of "susceptible" and "unsusceptible" mice

The self-assembly of 3,4-benzpyrene hydroxylase system from the 3-methylcholanthrene-induced liver microsomes of $\text{C57Bl}\text{6}$ mice and ($\text{C57Bl}\text{6}\text{×}\text{DBA}\text{2}\text{)F}{}_1$ hybrids has been characterized by much higher efficiency than that one from control microsomes of these mice. This phenomenon was not observed in microsomes of $\text{DBA}\text{2}$ mice. These data suggest that the regulation of aggregation process during the molecular morphogenesis of endoplasmic membranes in mice is of a dominantly inherited character.     

Female dimorphism in honey-bee larvae with respect to glucose metabolism

The rate of conversion of glucose-1-¹⁴C and glucose-6-¹⁴C to ¹⁴CO₂ and lipid was monitored in queen and worker larvae between 48 and 96 hr of age. A definite dimorphism in glucose metabolism between castes was established. Worker larvae 72 hr of age have a much greater $\text{C}{}_6\text{C}{}_1$ ratio than do queen larvae of the same age. The ratios were of the same order of magnitude for both castes of larvae younger or older than 72 hr. Queen larvae were shown to have a greater rate of lipid synthesis than worker larvae.     

The relation between Krogh and compartmental transport models

The meaning of compartmental concentration is intuitively simple in well-stirred compartment models with uniform concentration but not so in the general case. This meaning may be better understood by relating the general compartmental model to a spatially explicit one such as the Krogh cylinder model. We show that compartmental equations result directly by spatial averaging of the Krogh partial differential equations. Intercompartmental transport is usually stated as flux is proportional to the capillary-tissue concentration difference or $\text{J = ? (}\text{C}{}_{\mathrm{c}}\text{-}\text{C}{}_{\mathrm{T}}\text{)}$. We verify this simple equation by showing that flux in the Krogh model is also approximately first order and then derive the transport coefficient, ?, in terms of the geometry and diffusivity in the Krogh model. A relation between capillary and venous concentration or, for a gas, partial pressure is needed. For the highly diffusable, metabolic gas C0₂ this relation is $\text{P}{}_{\mathrm{c}}\text{= P}{}_{\mathrm{v}}\text{?}\text{M}\text{20K}{}_{\mathrm{c}}$ that is, capillary and venous partial pressures differ by one half the metabolic generation.     

Evidence for a protonmotive Q cycle mechanism of electron transfer through the cytochrome b-c1 complex.

A protein named oxidation factor can be reversibly removed from succinate-cytochrome $\text{c}$ reductase complex and shown to be required for electron transfer between succinate and cytochrome $\text{c}$. This protein is required for reduction of cytochrome $\text{c}{}_1$ and, in the presence of antimycin, for reduction of both cytochromes $\text{b}$ and $\text{c}{}_1$. These results are consistent with a protonmotive Q cycle mechanism in which the oxidation factor catalyzes electron transfer from reduced quinone to cytochrome $\text{c}{}_1$ and thus liberates from reduced quinone one of two protons required for energy conservation during electron transfer through the cytochrome $\text{b}\text{-}\text{c}{}_1$ complex.     

The polymorphic phase behaviour and miscibility properties of synthetic phosphatidylethanolamines

(1) The polymorphic phase behaviour of aqueous dispersions of various synthetic phosphatidylethanolamines, both singly and in mixtures, has been investigated by ³¹P-NMR. (2) $\text{14:0}\text{14:0}$ PE remains in the lamellar phase up to 90°C. $\text{18:1}{}_{\mathrm{<mtext>t</mtext>}}\text{18:1}{}_{\mathrm{<mtext>t</mtext>}}$ PE exhibits a lamellar to hexagonal (H_II) transition between 60°C and 63°C. For $\text{18:1}{}_{\mathrm{<mtext>c</mtext>}}\text{18:1}{}_{\mathrm{<mtext>c</mtext>}}$ PE, the lamellar to hexagonal (H_II) transition occurs between 7 and 12°C, whereas for $\text{18:2}{}_{\mathrm{<mtext>c</mtext>}}\text{18:2}{}_{\mathrm{<mtext>c</mtext>}}$ PE, the hexagonal (H_II) phase is the preferred structure above ?15°C. (3) Mixtures of $\text{18:1}{}_{\mathrm{<mtext>c</mtext>}}\text{18:1}{}_{\mathrm{<mtext>c</mtext>}}$ PE and $\text{18:1}{}_{\mathrm{<mtext>t</mtext>}}\text{18:1}{}_{\mathrm{<mtext>t</mtext>}}$ PE exhibit near-ideal miscibility behaviour. For mixtures of $\text{18:1}{}_{\mathrm{<mtext>c</mtext>}}\text{18:1}{}_{\mathrm{<mtext>c</mtext>}}$ PE and $\text{14:0}\text{14:0}$ PE there is evidence of fluid-solid immiscibility at temperatures below the gel-liquid crystalline transition temperature of the $\text{14:0}\text{14:0}$ PE component. Mixtures of $\text{18:2}{}_{\mathrm{<mtext>c</mtext>}}\text{18:2}{}_{\mathrm{<mtext>c</mtext>}}$ PE and $\text{18:1}{}_{\mathrm{<mtext>t</mtext>}}\text{18:1}{}_{\mathrm{<mtext>t</mtext>}}$ PE exhibit complex phase behaviour involving limited fluid-solid immiscibility at low temperatures and formation of a phase allowing isotropic motional averaging at higher temperatures. (4) ³¹P-NMR provides a graphic method for investigating the miscibility properties of mixed PE systems.     

Flow analysis in a biological system adopting the buffer capacitor concept.

The flow measurement of each component in each compartment is important in works on transport phenomena in a biological system. The method of flow measurement was studied adopting the capacitor concept derived from network thermodynamics.A biologically active component i in a compartment is defined as follows,

$\text{n}{}_{\mathrm{i}}\text{=n}{}_1\text{+n}{}_2\text{=c}{}_1\text{V+c}{}_2\text{V}$

where the total quantity ni consists of a measurable form n_i (free form, conc. c₁) and concealed form n₂ (conc, c₂). Capacitor for the species i of a compartment is defined as follows,

$\text{C=}\text{d}\text{n}{}_{\mathrm{i}}\text{d}\text{μ}{}_{\mathrm{i}}\text{=}\text{1+}\text{c}{}_2\text{c}{}_1\text{c}{}_1\text{dV}\text{dμ}{}_{\mathrm{i}}\text{+}\text{1+}\text{dc}{}_2\text{dc}{}_1\text{v}\text{dc}{}_1\text{dμ}{}_{\mathrm{i}}$

,

$\text{=Ac}{}_1\text{dV}\text{dμ}{}_{\mathrm{i}}\text{+BV}\text{d}\text{c}{}_1\text{d}\text{t}$

Thus flow of each component is expressed as,

$\text{J}{}_{\mathrm{i}}\text{=}\text{d}\text{n}{}_{\mathrm{i}}\text{d}{}_{\mathrm{i}}\text{=}\text{d}\text{n}{}_{\mathrm{i}}\text{dμ}{}_{\mathrm{i}}\text{dμ}\text{n}{}_{\mathrm{i}}\text{dt}\text{=C}\text{d}\text{μ}{}_{\mathrm{i}}\text{dt}$

,

$\text{=Ac}{}_1\text{d}\text{V}\text{dt}\text{+BV}\text{d}\text{c}{}_1\text{dt}$

Method of determination of capacitor coefficients A and B by titration experiment was also considered. For an experimental case, the capacitance for H⁺ of blood compartment was determined. The relationship between the capacitor concept and the buffer value of Van Slyke was discussed.     

Restoration of pool function type behavior to succinate dehydrogenase having latent reconstitutive activity in ubiquinol-cytochrome c reductase complex

Mitochondrial ubiquinol-cytochrome $\text{c}$ reductase complex contains small amounts of succinate dehydrogenase. Estimates from electrophoresis indicate there is one dehydrogenase per eight complexes. This dehydrogenase transfers electrons to the $\text{b}$-$\text{c}{}_1$ complex poorly, as judged by low succinate-ubiquinone and succinate-cytochrome $\text{c}$ reductase activities. Electron transfer to the $\text{b}$-$\text{c}{}_1$ complex is restored by reconstitution of the complex with phospholipid. This phospholipid dependent restoration of electron transfer indicates that either reconstitutive activity of the dehydrogenase is preserved under conditions where electron transfer is absent, or that addition of phospholipid allows one dehydrogenase to transfer electrons to multiple $\text{b}$-$\text{c}{}_1$ complexes.     

Microcalorimetric studies of the interactions between cytochromes c and c1 and of their interactions with phospholipids

Thermotropic properties of purified cytochrome $\text{c}{}_1$ and cytochrome $\text{c}$ have been studied by differential scanning calorimetry under various conditions. Both cytochromes exhibit a single endothermodenaturation peak in the differential scanning calorimetric thermogram. Thermodenaturation temperatures are ionic strength, pH, and redox state dependent. The ferrocytochromes are more stable toward thermodenaturation than the ferricytochromes. The enthalpy changes of thermodenaturation of ferro- and ferricytochrome $\text{c}{}_1$ are markedly dependent on the ionic strength of the solution. The effect of the ionic strength of solution on the enthalpy change of thermodenaturation of cytochrome $\text{c}$ is rather insignificant. The formation of a complex between cytochromes $\text{c}$ and $\text{c}{}_1$ at lower ionic strength causes a significant destabilization of the former and a slight stabilization of the latter. The destabilization of cytochrome $\text{c}$ upon mixing with cytochrome $\text{c}{}_1$ was also observed at high ionic strength, under which conditions no stable complex was detected by physical separation. This suggests formation of a transient complex between these two cytochromes. When cytochrome $\text{c}$ was complexed with phospholipids, no change in the thermodenaturation temperature was observed, but a great increase in the enthalpy change of thermodenaturation resulted.     

Effect of para-chloromercuribenzenesulfonic acid and temperature on cell water osmotic permeability of proximal straight tubules

The apparent Arrhenius energy of activation ($\text{E}{}_{\mathrm{<mtext>a</mtext>}}$) of the water osmotic permeability ($\text{P}{}_{\mathrm{<mtext>os</mtext>}}{}^{\mathrm{<mtext>c</mtext>}}$) of the basolateral plasma cell membrane of isolated rabbit proximal straight tubules has been measured under control conditions and after addition of 2.5 mM of the sulfhydryl reagent, para-chloromercuribenzenesulfonic acid (pCMBS), of mersalyl and of dithiothreitol. $\text{E}{}_{\mathrm{<mtext>a</mtext>}}$ (kcal/mol) was $\text{3.2 ± 1.4}$ (controls) and $\text{9.2 ± 2.2}$ (pCMBS), while $\text{P}{}_{\mathrm{<mtext>os</mtext>}}{}^{\mathrm{<mtext>c</mtext>}}$ decreased with pCMBS to $\text{0.26 ± 0.17}$ of its control value. Mersalyl also decreased $\text{P}{}_{\mathrm{<mtext>os</mtext>}}{}^{\mathrm{<mtext>c</mtext>}}$ both in vitro and in vivo (using therapeutical doses). These actions of pCMBS and mersalyl were quickly reverted with 5 mM dithiothreitol and prevented by 0.1 M thiourea. $\text{E}{}_{\mathrm{<mtext>a</mtext>}}$ for free viscous flow is 4.2 and greater than 10 for non-pore-containing lipid membranes. By analogy with these membranes and with red blood cells, where similar effects of pCMBS on $\text{P}{}_{\mathrm{<mtext>os</mtext>}}$ are observed, it is concluded that cell membranes of the proximal tubule are pierced by aqueous pores which are reversibly shut by pCMBS. Part of the action of mercurial diuretics can be explained by their action on $\text{P}{}_{\mathrm{<mtext>os</mtext>}}{}^{\mathrm{<mtext>c</mtext>}}$.     

Binding of the structural protein soc to the head shell of bacteriophage T4

Qβ plus strands with a 70 S ribosome bound to the coat cistron initiation site were used as template for Qβ replicase. Minus strand synthesis proceeded until the replicase reached the ribosome. The ribosome was removed and elongation was continued in a substrate-controlled, stepwise fashion. The nucleotide analog N⁴-hydroxyCMP was introduced into the positions complementary to the third and fourth nucleotides of the coat cistron. The minus strands were elongated to completion, purified and used as template for Qβ replicase. The final plus strand preparation consisted of four species, with the sequences -A-U-G-G- (wild type), -A-U-A-G- (mutant C₃), -A-U-G-A- (mutant C₄) and -A-U-A-A- (mutant $\text{C}{}_3\text{C}{}_4$) at the coat initiation site. The ribosome binding capacity of the mutant RNAs relative to wild type was <0.1 (C₃), 3.2 (C₄) and 0.3 ($\text{C}{}_3\text{C}{}_4$). The finding that mutant C₃ no longer formed an initiation complex suggests that the interaction of the ribosome binding site with fMet-tRNA plays an essential role in the formation of the 70 S initiation complex. The fact that mutant C₄ RNA bound more efficiently than wild type, and that mutant $\text{C}{}_3\text{C}{}_4$ RNA showed substantial ribosome binding capacity whereas the single mutant C₃ did not, can be explained by assuming that an A residue following the A-U-G triplet interacts with a complementary U residue in the anticodon loop sequence. In the case of $\text{C}{}_3\text{C}{}_4$ this additional base-pair may offset the reduced codon-anticodon interaction resulting from the modification of the A-U-G codon.     

The concept of high- and low-affinity reactions in bovine cytochrome c oxidase steady-state kinetics

(1) Analysis of the data from steady-state kinetic studies shows that two reactions between cytochrome c and cytochrome c oxidase sufficed to describe the concave Eadie-Hofstee plots ($\text{K}{}_{\mathrm{<mtext>m</mtext>}}\text{? 1 · 10}{}^{\mathrm{?8}}\text{M}$ and $\text{K}{}_{\mathrm{<mtext>m</mtext>}}\text{? 2 · 10}{}^{\mathrm{?5}}\text{M}$). It is not necessary to postulate a third reaction of $\text{K}{}_{\mathrm{<mtext>m</mtext>}}\text{? 10}{}^{\mathrm{?6}}\text{M}$. (2) Change of temperature, type of detergent and type of cytochrome c affected both reactions to the same extent. The presence of only a single catalytic cytochrome c interaction site on the oxidase could explain the kinetic data. (3) Our experiments support the notion that, at least under our conditions (pH 7.8, low-ionic strength), the dissociation of ferricytochrome c from cytochrome c oxidase is the rate-limiting step in the steady-state kinetics. (4) A series of models, proposed to describe the observed steady-state kinetics, is discussed.     

Comparison of the promoting activity of pristane and n-alkanes in skin carcinogenesis with their physical effects on micellar models of biological membranes

In 1976 (Horton, A.W., Butts, C.K. and Schuff, A.R. (1976) Colloid Interface Sci. 5, 159–168) we assayed pristance (2,6,10,14-tetramethylpentadecane) in a model interfacial system that has given excellent correlation with cocarcinogenic activity among $\text{n-}\text{alkanes}$, as tested in cycloalkane diluents. It was predicted that this branched-chain derivative of the diterpenes would have higher activity than $\text{n-}\text{C}{}_{18}\text{H}{}_{38}$, one of the most cocarcinogenic of the $\text{n-}\text{alkanes}$ in such diluents. Pristane was compared with $\text{n-}\text{C}{}_{18}\text{H}{}_{38}$ and two other $\text{n-}\text{alkanes}$ for their promoting activities in cyclohexane for C3H male mice after a single application of 7,12-dimethylbenz$\text{[a]}\text{anthracene}$. The branched-chain alkane proved to be more active. 20% $\text{n-}\text{tetracosane}$ in cyclohexane was inactive, which correlated with its effects in this diluent in the physical assay system. The promoting activity of 75% $\text{n-}\text{octane}$ in cyclohexane, predicted by the physical assay, was confirmed by tests on mice. The combined by-products of the synthesis of tetracosane, including C₁₂ alkanes and alkenes, C₁₉ and C₂₀ alkylbenzenes, and C₂₄ alkenes, proved to be a very active promoter. However, a mixture in cyclohexane of purified tetracosane with this composite of potential impurities was inactive. From the alkanes behavior in physical systems involving vatious membrane phospholipids and steroids, it is hypothesized that the primary step in their biological activity is a chain-chain interaction with membrane lipids that alters the properties of liquid-crystalline phases at aqueous interfaces. Resulting changes in the microfluidity of the lipid phase and the lateral mobility of critical hormone receptors and enzyme systems, such as the nucleotidyl cyclases, would perturb control systems that maintain the normal behavior of the initiated cell. Thus, its progression to a proliferating neoplasm may be favored.     

A chloride requirement for Na+-dependent amino-acid transport by brush border membrane vesicles isolated from the intestine of a mediterranean teleost (Boops salpa)

The uptake of d-glucose, 2-aminoisobutyric acid and glycine was studied with intestinal brush border membrane vesicles of a marine herbivorous fish: Boops salpa. The uptake of these three substances is stimulated by an Na⁺ electrochemical gradient ($\text{C}{}_{\mathrm{<mtext>out</mtext>}}\text{C}{}_{\mathrm{<mtext>in</mtext>}}$). For glucose, an increase of the electrical membrane potential generated by a concentration gradient of the liposoluble anion, SCN^?, increases the Na⁺-dependent transport. This responsiveness to the membrane potential was confirmed by valinomycin. Differently from glucose, uptake of glycine and 2-aminoisobutyric acid requires, besides the Na⁺ gradient, the presence of Cl^? on the external side of the vesicles. In the absence of Cl^?, amino acid uptake is not stimulated by the Na⁺ gradient and is not influenced by an electrical membrane potential generated by SCN^? gradient ($\text{C}{}_{\mathrm{<mtext>out</mtext>}}\text{>C}{}_{\mathrm{<mtext>in</mtext>}}$) or by a K⁺ diffusion potential ($\text{C}{}_{\mathrm{<mtext>in</mtext>}}\text{>C}{}_{\mathrm{<mtext>out</mtext>}}$). This Cl^? requirement differs from the Na⁺ requirement, since a Cl^? gradient ($\text{C}{}_{\mathrm{<mtext>out</mtext>}}\text{>C}{}_{\mathrm{<mtext>in</mtext>}}$) does not result in an accumulation of glycine or 2-aminoisobutyric acid similar to that produced by an Na⁺ gradient.     

The effect of formate on cytochrome aa3 and on electron transport in the intact respiratory chain

1. Formate inhibits cytochrome $\text{c}$ oxidase activity both in intact mitochondria and submitochondrial particles, and in isolated cytochrome $\text{aa}{}_3$. The inhibition increases with decreasing pH, indicating that HCOOH may be the inhibitory species.2. Formate induces a blue shift in the absorption spectrum of oxidized cytochrome $\text{aa}{}_3\text{(a}{}^{\mathrm{3+}}\text{a}{}_3{}^{\mathrm{3+}}$) and in the half-reduced species ($\text{a}{}^{\mathrm{2+}}\text{a}{}_3{}^{\mathrm{3+}}$). Comparison with cyanide-induced spectral shifts, towards the red, indicates that formate and cyanide have opposite effects on the $\text{aa}{}_3$ spectrum, both in the fully oxidized and the half-reduced states. The formate spectra provide a new method of obtaining the difference spectrum of $\text{a}{}_3{}^{\mathrm{2+}}$ minus $\text{a}{}_3{}^{\mathrm{3+}}$, free of the difficulties with cyanide (which induces marked high → low spin spectral shifts in cytochrome $\text{a}{}_3{}^{\mathrm{3+}}$) and azide (which induces peak shifts of cytochrome $\text{a}{}^{\mathrm{2+}}$ towards the blue in both α- and Soret regions).3. The rate of formate dissociation from cytochrome $\text{a}{}^{\mathrm{2+}}\text{a}{}_3{}^{\mathrm{3+}}\text{-}\text{HCOOH}$ is faster than its rate of dissociation from $\text{a}{}^{\mathrm{3+}}\text{a}{}_3{}^{\mathrm{3+}}\text{-}\text{HCOOH}$, especially in the presence of cytochrome $\text{c}$. The $\text{K}{}_{\mathrm{<mtext>i</mtext>}}$ for formate inhibition of respiration is a function of the reduction state of the system, varying from 30 mM (100% reduction) to 1 mM (100% oxidation) at pH 7.4, 30 °C.4. Succinate-cytochrome $\text{c}$ reductase activity is also inhibited by formate, in a reaction competitive with succinate and dependent on [formate]².5. Formate inhibition of ascorbate plus $\text{N,N,N′,N′-}\text{tetramethyl}\text{-p-}\text{phenyl-enediamine}$ oxidation by intact rat liver mitochondria is partially released by uncoupler addition. Formate is permeable through the inner mitochondrial membrane and no differences in ‘on’ or ‘off’ inhibition rates were observed when intact mitochondria were compared with submitochondrial particles.6. NADH-cytochrome $\text{c}$ reductase activity is unaffected by formate in submitochondrial particles, but mitochondrial oxidation of glutamate plus malate is subject both to terminal inhibition at the cytochrome $\text{aa}{}_3$ level and to a slow extra inhibition by formate following uncoupler addition, indicating a third site of formate action in the intact mitochondrion.     

Anaerobic stimulation of sugar transport in avian erythrocytes

The kinetic parameters of the sugar transport in avian erythrocytes were evaluated under aerobic and anaerobic conditions. In anaerobic cells, transport measurements with $\text{3-O-[}{}^{14}\text{C}\text{]}$ methylglucose resulted in a set of similar dissociation-like constants. Thus the Michaelis constants of $\text{3-O-[}{}^{14}\text{C}\text{]}$ methylglucose entry and exit, $\text{K}{}_{\mathrm{<mtext>so</mtext>}}$ and $\text{K}{}_{\mathrm{<mtext>si</mtext>}}$, were 8 and 7 mM, respectively. The equilibrium exchange constant, $\text{B}{}_{\mathrm{<mtext>s</mtext>}}$, and the counterflow constant, $\text{R}{}_{\mathrm{<mtext>s</mtext>}}$, were 9 and 11 mM, respectively. The activity constant for $\text{3-O-}\text{methylglucose}$ transport, $\text{F}{}_{\mathrm{<mtext>s</mtext>}}$, defined as $\text{V/K}{}_{\mathrm{<mtext>m</mtext>}}$, was 4 ml/h per g. This set of kinetic constants was compatible with a symmetrical mobile-carrier model. In contrast, the Michaelis constant for glucose entry, $\text{K}{}_{\mathrm{<mtext>go</mtext>}}$, was 2 mM and less than the counterflow constant, $\text{R}{}_{\mathrm{<mtext>g</mtext>}}$ (8 mM). This result could be accounted for by slower movement of the glucose-carrier complex than the free carrier. The activity constant for glucose transport, $\text{F}{}_{\mathrm{<mtext>g</mtext>}}$, was 5 ml/h perg.Under aerobic conditions, two of the dissociation-like constants ($\text{K}{}_{\mathrm{<mtext>si</mtext>}}$ and $\text{B}{}_{\mathrm{<mtext>s</mtext>}}$) for $\text{3-O-}\text{methylglucose}$ transport were significantly larger than those obtained in anaerobic cells, but the remaining two ($\text{K}{}_{\mathrm{<mtext>so</mtext>}}$ and $\text{R}{}_{\mathrm{<mtext>s</mtext>}}$) remained unchanged. The values, for $\text{K}{}_{\mathrm{<mtext>so</mtext>}}\text{, K}{}_{\mathrm{<mtext>si</mtext>}}\text{, B}{}_{\mathrm{<mtext>s</mtext><mtext>\; and</mtext>}}\text{R}{}_{\mathrm{<mtext>s</mtext>}}$ were 8, 26, 20 and 8 mM, respectively. The activity constant, $\text{F}{}_{\mathrm{<mtext>s</mtext>}}$, decreased to 2 ml/h per g. These changes in kinetic constants were consistent with the hypothesis that anoxia accelerated sugar transport by releasing free carrier that was previously sequestered on the inside of the cell membrane.     

A fluctuation analysis study of the development of amiloride-sensitive Na+ transport in the skin of larval bullfrogs (Rana catesbeiana)

In the presence of the Na⁺-channel blocker amiloride, the short-circuit current across the skins of bullfrog tadpoles in metamorphic stages XIX–XXIV was subjected to fluctuation analysis. The resulting power spectra contained a Lorentzian component of which the plateau value ($\text{S}{}_0$) decreased while the corner frequency ($\text{f}{}_{\mathrm{<mtext>c</mtext>}}$) increased as the mucosal amiloride concentration was increased from 0.5 to 24 μM. From the linear relationship between the $\text{f}{}_{\mathrm{<mtext>c</mtext>}}$ values and the amiloride concentrations it was possible to determine the binding ($\text{k′}{}_{01}$) and unbinding ($\text{k}{}_{10}$) constants for amiloride to its receptor on the Na⁺ channel. With these parameters as well as short-circuit current and $\text{S}{}_0$ values, the current through the individual Na⁺ channels ($\text{i}$) was calculated (average 0.58 pA). It did not increase significantly during late metamorphosis. The density of Na⁺ channels ($\text{M}$) in the apical membrane, on the other hand, increased significantly. It would appear that the increase in short-circuit current which occurs at this time is due primarily to an increase in amiloride-blockable Na⁺ channels. Unexpectedly, a Lorentzian component could be fitted to power spectra in amiloride-treated skins (stages XIX–XXI) which showed no amiloride-sensitive short-circuit current. Moreover, the typical increase in $\text{f}{}_{\mathrm{<mtext>c</mtext>}}$ with the amiloride concentration did not occur in these animals.     

Ubisemiquinone radicals from the cytochrome b-c1 complex of the mitochondrial electron transport chain--demonstration of QP-S radical formation

Stable ubisemiquinone radical(s) in the cytochrome $\text{b}\text{?}\text{c}{}_1$-II complex of bovine heart was observed following reduction by succinate in the presence of catalytic amounts of succinate dehydrogenase. The radical was abolished by addition of antimycin A, but a residual radical remained in the presence of excess exogenous Q₂. The radical showed an EPR signal of g = 2.0046 ± .003 at X band (～9.4 GHz) with no resolved hyperfine structure and had a line width of 8.1 ± .5 Gauss at 23°C. The Q band (35 GHz) spectra showed wellresolved $\text{g}$-anisotropy and had a field separation between derivative extrema of 26 ± 1 Gauss. This radical is evidently from QP-C. These observations substantiate that the radical is immobilized and bound to a protein. The QP-S radical was demonstrated in the cytochrome $\text{b}\text{-}\text{c}{}_1$-II complex only in the presence of more than a catalytic amount of succinate dehydrogenase and cytochrome $\text{b}\text{-}\text{c}{}_1$. This signal was not antimycin a inhibitory. The signal amplitude paralleled the reconstitutive enzymic activity of succinate-cytochrome $\text{c}$ reductase from succinate dehydrogenase and the cytochrome $\text{b}\text{-}\text{c}{}_1$-II complex.     

A convective mass transfer model for determining intestinal wall permeabilities: laminar flow in a circular tube

A convective mass transfer model as analyzed and developed for use in determining intestinal wall permeabilities from external perfusion experiments. Analysis of the model indicates that the ratio of the exit to inlet concentration $\text{C}{}_{\mathrm{m}}\text{C}{}_0$ is a function of only two dimensionless independent variables, the wall permeability, $\text{P}{}_{\mathrm{w}}{}^1$ and Graetz number, Gz = πDL/2Q. The Graetz number contains the independent variables of interest, length, diflusivity, and flow rate. The radius of the intestine is included implicitly in the flow rate. Since $\text{C}{}_{\mathrm{m}}\text{C}{}_0$ and Gz are the experimental quantities, and the solution to the model system contains P_ω¹ implicitly, a convenient approximate method is developed which allows a direct calculation of P_ω¹. This method is in error by 10–20% in the worst cases. The approach is illustrated by application to the determination of the wall permeabilities for two non polar compounds.     

Trypanosoma vivax: Courses of infection with three stabilates in inbred mouse strains

The courses of infection in inbred mouse strains were compared following infection with three Stabilates of high, intermediate, and low virulence of Trypanosoma vivax stock Zaria Y486. Mouse strains could only be shown to differ in their resistance to T. vivax infections as judged by the height of the initial parasitemia and survival times when a trypanosome population of low or intermediate virulence was used. A T. vivax population of high virulence was uniformly lethal. Comparison of lytic antibody titers between groups of resistant ($\text{C}\text{57}\text{B}\text{1}\text{6}$) and susceptible ($\text{Balb}\text{c}$) mice did not show any significant differences in titers of the surviving mice but the mice in either group which did not control the initial parasitemia had lower lytic antibody titers than those which did. A significantly larger number of $\text{Balb}\text{c}$ mice failed to control the initial infection as compared to the $\text{C}\text{57}\text{B}\text{1}\text{6}$. Treatment with cyclophosphamide did not ablate differences in susceptibility between the two strains. The use of congenic mice showed that these differences in susceptibility were not related to differences in the major histocompatibility complex between these strains.