Analysis of the kinetics of electron transfer reactions of hemoglobin and myoglobin with inorganic complexes.

The kinetics of methemoglobin reduction by Fe(EDTA)^2? have been studied and found to follow a second order rate law with k = 29.0 $\text{M}$^?1 s^?1 [25°C, μ = 0.2 $\text{M}$, pH 7.0 (phosphate)], $\text{ΔH}{}^3\text{= 5.5 ± 0.7 kcal/mol}$, and $\text{ΔS}{}^2\text{= ?33 ± 2 e.u.}$. The electrostatics-corrected self-exchange rate constant (k₁₁^corr) for hemoglobin based on the Fe(EDTA)^2? cross-reaction is 2.79×10^?3$\text{M}$^?1 s^?1. This rate constant is compared with others reported for a water-soluble iron porphyrin and calculated from published data for the reactions of myoglobin and hemoglobin with Fe(EDTA)^2? and Fe(CDTA)^2?/?. The k₁₁^corr values for these systems range over ten orders of magnitude with heme ? myoglobin > hemoglobin.     

On the effect of rfe mutation on the biosynthesis of the 08 and 09 antigens of E. coli.

From phosphomannose isomerase-less mutants of $\text{E. coli}$ strains 08 and 09, $\text{rfe}{}^{\mathrm{?}}$ derivatives were constructed by recombination with a $\text{Salmonella rfe}{}^{\mathrm{?}}$ donor. In contrast to membranes from the parent $\text{E. coli}$ strains, those from the $\text{rfe}{}^{\mathrm{?}}$ recombinants did not synthesize the 08 or 09 mannan from GDP mannose $\text{in vitro}$. They could, however, be restored to biosynthetic activity with butanol extracts from the $\text{E. coli rfe}{}^{\mathrm{+}}$ bacteria. This indicated that the $\text{rfe}$ mutation affects the synthesis of a hydrophobic acceptor.     

Temperature-sensitive mutations in Drosophila melanogaster. 8. Temperature-sensitive periods of the lethal and morphological phenotypes of selected combinations of notch-locus mutations

Temperature-shift experiments were performed on five Notch-locus genotypes with temperature-sensitive phenotypes. The results show that temperature-sensitive periods (TSPs) for lethality may occur at any developmental stage: (1) $\text{N}{}^{\mathrm{g11}}\text{N}{}^{\mathrm{g11}}$;Dp^51b7 having a short embryonic TSP for lethality, (2) $\text{Ax}{}^{16172}\text{N}{}^{\mathrm{?40}}$ having a second-instar TSP for lethality, and (3) $\text{N}{}^{\mathrm{?103}}\text{fa}{}^{\mathrm{no}}$ with a long, possibly polyphasic, TSP, beginning in the embryonic stage and ending in the pupal stage. On the other hand, TSPs for adult morphological phenotypes appear to be restricted to the third larval instar: (1) $\text{Ax}{}^{16172}\text{N}{}^{\mathrm{?40}}$ having third-instar TSPs for wing vein gapping and ocellar bristle loss, and (2) $\text{N}{}^{\mathrm{?103}}\text{spl}$ having third-instar TSPs for eye facet disarray, wing notching, bristle number variation, and fusion of tarsal segments. The significance of these results is discussed in terms of the role of the Notch locus in development.     

Kinetics of phospholipid exchange between bilayer membranes

In an accompanying publication by Duckwitz-Peterlein, Eilenberger and Overath ((1977) Biochim. Biophys. Acta 469, 311–325) it is shown that the exchange of lipid molecules between negatively charged vesicles consisting of total phospholipid extracts from Escherichia coli occurs by the transfer of single lipid monomers or small micelles through the water. Here a kinetic interpretation is presented in terms of a rate constant, $\text{k}{}_{\mathrm{?}}$, for the escape of lipid molecules from the vesicle bilayer into the water. The evaluated rate constants are $\text{k}{}_{\mathrm{?}}{}^{\mathrm{<mtext>P</mtext>}}\text{= (0.86 ± 0.05) · 10}{}^{\mathrm{?5}}\text{s}{}^{\mathrm{?1}}$ and $\text{k}{}_{\mathrm{?}}{}^{\mathrm{<mtext>E</mtext>}}\text{= (1.09 ± 0.13) · 10}{}^{\mathrm{?6}}\text{s}{}^{\mathrm{?1}}$ for phospholipid molecules with $\text{trans-}\text{Δ}{}^9\text{-hexadecenoate}$ and $\text{trans-}\text{Δ}{}^9\text{-octadecenoate}$, respectively, as the predominant acyl chain component. The rate constants are discussed in terms of the acyl chain and polar head group composition of the lipids.     

Cyclic AMP transport in human erythrocyte ghosts

10^?5 M cyclic AMP has high permeability in human erythrocyte ghosts ($\text{p = 0.061 · 10}{}^{\mathrm{?6}}\text{cm}\text{·}\text{s}{}^{\mathrm{?1}}$). Saturation of influx and efflux occurs. $\text{K}{}_{\mathrm{<mtext>z</mtext><mtext>t</mtext>}}{}^{\mathrm{<mtext>oi</mtext>}}\text{= 4.43}\text{mM}$. $\text{V}{}_{\mathrm{zt}}{}^{\mathrm{oi}}\text{= 259.6 μ}\text{M · min}{}^{\mathrm{?1}}$. $\text{K}{}_{\mathrm{<mtext>z</mtext><mtext>t</mtext>}}{}^{\mathrm{<mtext>io</mtext>}}\text{= 0.475 μ}\text{M}$. $\text{V}{}_{\mathrm{<mtext>z</mtext><mtext>t</mtext>}}{}^{\mathrm{<mtext>io</mtext>}}\text{= 28.3 μ}\text{M · min}{}^{\mathrm{?1}}$ at 30°C. Equilibrium exchange entry of cyclic AMP has similar kinetics to zero trans influx, though the system does show counterflow. Cythochalasin B is an apparent competitive inhibitor of cyclic AMP exit. ($\text{K}{}_{\mathrm{<mtext>i</mtext>}}\text{= 3.9 · 10}{}^{\mathrm{?7}}\text{M}$).Control experiments indicated that cyclic AMP remains intact during incubation with red blood cell ghosts and is contained within the intravesicular space during the transport experiments.     

Reactivity of chemically generated superoxide radical anion with peroxides as determined by competition kinetics

A steady-state competition system has been developed to investigate the reactions of the superoxide radical anion ($\text{O}{}_2{}^{\mathrm{<mtext>?</mtext>}}$) with various peroxides, including the so-called Haber-Weiss reaction. Potassium superoxide dissolved in an oxygen-free solution of DMSO containing 18-dicyclohexyl-6-crown, is the source of $\text{O}{}_2{}^{\mathrm{<mtext>?</mtext>}}$. High pressure liquid chromatography is used as an assay system for $\text{O}{}_2{}^{\mathrm{<mtext>?</mtext>}}$ reactivity, to detect and quantitate the yield of anthracene, formed as a major product in the reaction between $\text{O}{}_2{}^{\mathrm{<mtext>?</mtext>}}$ and 9,10-dihydroanthrancene. Decrease in anthracene yields, in the presence of peroxide, may be used to indicate a possible competing reaction between $\text{O}{}_2{}^{\mathrm{<mtext>?</mtext>}}$ and added peroxide. Complications involving peroxide-stimulated formation of anthraquinone derivatives are discussed. No evidence for a competing reaction between $\text{O}{}_2{}^{\mathrm{<mtext>?</mtext>}}$ and peroxide can be detected up to a 10-fold excess of peroxide over 9,10-dihydroanthracene.     

Properties of bilayer membranes in the presence of dipicrylamine. A comparative study by optical absorption and electrical relaxation measurements

In order to test the question if a pool of lipophilic ions may exist in black lipid membranes which cannot be detected by electrical relaxation measurements we have performed simultaneously measurements of the optical absorption of a lipophilic ion. The absorbance of membrane-bound dipicrylamine at 410 nm was measured with a sensitive spectrophotometer which can detect absorbance changes $\text{? 4 · 10}{}^{\mathrm{?5}}$. A minimal concentration of about 6 · 10¹¹ dipicrylamine ions per cm² of the membrane could be detected with this instrument. The dipicrylamine concentration in the membrane obtained with the optical method $\text{N}{}_{\mathrm{<mtext>t</mtext>}}{}^{\mathrm{<mtext>opt</mtext>}}$ is compared with the concentrations $\text{N}{}_{\mathrm{<mtext>t</mtext>}}{}^{\mathrm{<mtext>el</mtext>}}$ obtained from simultaneous electrical relaxation measurements. $\text{N}{}_{\mathrm{<mtext>t</mtext>}}{}^{\mathrm{<mtext>opt</mtext>}}$ and $\text{N}{}_{\mathrm{<mtext>t</mtext>}}{}^{\mathrm{<mtext>el</mtext>}}$ agreed at low dipicrylamine concentrations (10^?8–10^?7 M in the aqueous phase) and showed saturation at higher concentrations (up to 5 · 10^?6 M). In the saturation range $\text{N}{}_{\mathrm{<mtext>t</mtext>}}{}^{\mathrm{<mtext>opt</mtext>}}$ was maximally four times higher than $\text{N}{}_{\mathrm{<mtext>t</mtext>}}{}^{\mathrm{<mtext>el</mtext>}}$. The significance of this difference is discussed together with general aspects of the saturation phenomenon.     

Bicarbonate ion-ATPase in rat liver cell fractions

The distribution of $\text{HCO}{}_3{}^{\mathrm{?}}\text{-}\text{ATPase}$ activity was studied in cell fractions prepared from homogenates of rat liver. The level of mitochondrial contamination in the microsomal fraction depended on the fractionation procedure and on the method of homogenization. With proper care, microsomes with undetectable mitochondrial contamination could be prepared. These microsomes had no detectable $\text{HCO}{}_3{}^{\mathrm{?}}\text{-ATPase}$ activity. Approximately 85 % of the total $\text{HCO}{}_3{}^{\mathrm{?}}\text{-ATPase}$ activity of the post 6000 x g · min supernatant was recovered in the mitochondrialfraction. The properties of this mitochondrial $\text{HCO}{}_3{}^{\mathrm{?}}\text{-}\text{ATPase}$ were not distinguishable from those of the various microsomal $\text{HCO}{}_3{}^{\mathrm{?}}\text{-}\text{ATPase}$ previously described by other investigators.     

Chemical and spectroscopic conformation of an exogenous ligand bridge in half met hemocyanin.

Half $\text{met-N}{}_3{}^{\mathrm{?}}$ hemocyanin is shown to undergo a unique change at the Cu(II)?Cu(I) active site with temperature, exhibiting class II mixed valent properties at low temperature (The appearance of an intense near IR intervalence-transfer transition and a delocalized EPR spectrum). This requires a Cu(II)NNNCu(I) bridging geometry. The effects of CO coordination to half $\text{met-N}{}_3{}^{\mathrm{?}}$, combined with the presence of a low energy $\text{N}{}_3{}^{\mathrm{?}}\text{→ Cu(II)}$ charge transfer transition, demonstrate that azide is also bridging at room temperature. Finally, half $\text{met-N}{}_3{}^{\mathrm{?}}$ is found to be capable of coordination of a second $\text{N}{}_3{}^{\mathrm{?}}$ at the copper(II) site.     

The loss of the phoS periplasmic protein leads to a change in the specificity of a constitutive inorganic phosphate transport system in Escherichia coli

The phoS periplasmic protein, implicated in alkaline phosphatase regulation, is shown to be involved in inorganic phosphate (Pi) transport in $\text{E. coli}$. Although $\text{pho}\text{S}{}^{\mathrm{?}}$ cells dependent upon the PST system for Pi transport can grow in minimal medium with 1 mM Pi as source of phosphorus, the affinity of these cells for Pi is greatly reduced; Km = 18 μM compared with Km = 0.4 μM for $\text{phoS}{}^{\mathrm{+}}$ cells. $\text{pho}\text{S}{}^{\mathrm{?}}$ cells dependent upon the PST Pi transport system acquire the ability to accumulate Asi from the medium in contrast to $\text{pho}\text{S}{}^{\mathrm{+}}$ cells which exclude this toxic anion. It would appear that the periplasmic phoS protein is not essential for Pi accumulation but is involved in maintaining the specificity of the PST Pi transport system.     

Effect of angiotensin II on artificial lipid membranes

(5-Isoleucine)-angiotensin II applied to black lipid membranes produced current fluctuations varying between $\text{Δ>G = 5 · 10}{}^{\mathrm{?11}}\text{Ω}{}^{\mathrm{?}}$ and 3.5 · 10^?10 Ω^?1. These fluctuations depend on the voltage and the hydrostatic pressure. The membrane resistance is lowered by $\text{Δ>R = 6.1 · 10}{}^7\text{Ω · cm}{}^2$. With (5-isoleucine, 8-leucine)-angiotensin II the jumps are of a single amplitude ($\text{Δ>G = 2 · 10}{}^{\mathrm{?10}}\text{Ω}{}^{\mathrm{?1}}$). In both cases water and ions are transported across the membrane.     

Dopamine-stimulated cyclic AMP and binding of [3H]dopamine in acini from dog pancreas

Dispersed acini from dog pancreas were used to examine the ability of dopamine to increase cyclic AMP cellular content and the binding of [³H]dopamine. Cyclic AMP accumulation caused by dopamine was detected at 1·10^?8 M and was half-maximal at $\text{7.9±3.4·10}{}^{\mathrm{?7}}\text{M}$. The increase at 1·10^?5 M, (7.5-fold) was equal to the half-maximal increase caused by secretin at 1·10^?9 M. Haloperidol, a dopaminergic receptor antagonist inhibited cyclic AMP accumulation caused by dopamine. The IC₅₀ value for haloperidol, calculated from the inhibition of cyclic AMP increase caused by 1·10^?5 M dopamine was $\text{2.3±0.9·10}{}^{\mathrm{?6}}\text{M}$. Haloperidol did not alter basal or secretin-stimulated cyclic AMP content. [³H]Dopamine binding was studied on the same batch of cells as cyclic AMP accumulation. At 37°C, it was rapid, reversible, saturable and stereospecific. The $\text{K}{}_{\mathrm{<mtext>d</mtext>}}$ value for high affinity binding sites was $\text{0.43±0.1·10}{}^{\mathrm{?7}}\text{M}$ and $\text{4.7±1.6·10}{}^{\mathrm{?7}}\text{M}$ for low affinity binding sites. The concentration of drugs necessary to inhibit specific binding of dopamine by 50% was $\text{1.2±0.4·10}{}^{\mathrm{/t-7}}\text{M}$ noradrenaline, 2·10^/t-7 M epinine, $\text{4.1±1.8·10}{}^{\mathrm{/t-6}}\text{M}$ fluphenazine, $\text{8.0±1.6·10}{}^{\mathrm{/t-6}}\text{M}$ haloperidol, $\text{4.2±1.2·10}{}^{\mathrm{?6}}\text{M}$cis-flupenthixol, $\text{2.7±0.4·10}{}^{\mathrm{?5}}\text{M}$trans-flupenthixol, $\text{>1·10}{}^{\mathrm{?5}}\text{M}$ apomorphine, sulpiride, naloxone and isoproterenol.     

The permeability of the lysosomal membrane to small ions

The permeability of the lysosomal membrane to small anions and cations was studied at 37°C and pH 7.0 in a lysosomal-mitochondrial fraction isolated from the liver of untreated rats. The extent of osmotic lysis following ion influx was used as a measure of ion permeancy. In order to preserve electroneutrality, anion influx was coupled to an influx of K⁺ in the presence of valinomycin, and cation influx was coupled to an efflux of H⁺ using the protonophore $\text{3-tert-}\text{butyl-5,2′-dichloro-4′-nitrosalicilylanilide}$. Lysosomal lysis was monitored by observing the loss of latency of two lysosomal hydrolases.The order of permeability of the lysosomal membrane to anions was found to be $\text{SCN}{}^{\mathrm{?}}\text{> I}{}^{\mathrm{?}}\text{> CH}{}_3\text{COO}{}^{\mathrm{?}}\text{> Cl}{}^{\mathrm{?}}\text{≈ HCO}{}^{\mathrm{?}}{}_3\text{≈ P}{}_{\mathrm{i}}\text{> SO}{}_4{}^{\mathrm{2?}}$ and that to cations $\text{Cs}{}^{\mathrm{+}}\text{> K}{}^{\mathrm{+}}\text{> Na}{}^{\mathrm{+}}\text{> H}{}^{\mathrm{+}}$. These orders are largely in agreement with the lyotropic series of anions and cations.The implications of these findings for the mechanism by means of which a low intralysosomal pH is produced and maintained are discussed.     

A reaction between the superoxide free radical and lipid hydroperoxide in sodium linoleate micelles

The oxidation of unsaturated fatty acid micelles by the superoxide free radical ($\text{O}{}^{\mathrm{?}}{}_2$), during γ irradiation in the presence of formate, is kinetically distinct from oxidation by hydroxyl free radicals (HO.). The evidence suggests that a direct reaction between ($\text{O}{}^{\mathrm{?}}{}_2$) and lipid hydroperoxide initiates a chain oxidation process in the micelles. While tetranitromethane, which reacts rapidly with ($\text{O}{}^{\mathrm{?}}{}_2$), protects the micelles from oxidation, active superoxide dismutase is no more effective than its apoprotein, due to lack of penetration of the micellar environment. We discuss these findings in the light of recent literature, and with reference to their possible significance for biological systems.     

The solvent contribution to the free energy of protein--ligand interactions.

The intrinsic solvent contribution to the free energy of protein-ligand interactions in solution is shown to be related to a free energy per unit area term, obtained from analysis of the solution to gas phase process, and the change in accessible area on association. Analysis of the free energy data on a per unit area basis for the solution to gas phase process leads to the conclusion that the aliphatic CH₂ group is only slightly intrinsically hydrophobic, $\text{δΔG°/}\text{A}\text{?}{}^2\text{= 6}\text{cal mol}{}^{\mathrm{?1}}\text{A}\text{?}{}^2$, whereas the aromatic compound are actually intrinsically hydrophilic, $\text{δΔG°/}\text{A}\text{?}{}^2\text{= -26}\text{cal mol}{}^{\mathrm{?1}}\text{A}\text{?}{}^2$. This leads to the conclusion that, for the interaction of benzene, naphthalene and anthracene with the binding site of α-chymotrypsin, the ligand-solvent free energy contribution is actually unfavorable. Since the protein-solvent contribution is small or unfavorable, the central conclusion is that the solvent contribution to protein-ligand interactions is small or unfavorable and that it is the protein-ligand non-bonded interactions that provide the driving force for association.     

Respiration-driven proton translocation with nitrite and nitrous oxide in Paracoccus denitrificans

(1) $\text{H}$⁺/electron acceptor ratios have been determined with the oxidant pulse method for cells of denitrifying Paracoccus denitrificans oxidizing endogenous substrates during reduction of O₂, NO^?₂ or N₂O. Under optimal H⁺-translocation conditions, the ratios $\text{H}{}^{\mathrm{+}}\text{O}$, $\text{H}{}^{\mathrm{+}}\text{N}{}_2\text{O}$, $\text{H}{}^{\mathrm{+}}\text{NO}{}^{\mathrm{?}}{}_2$ for reduction to N₂ and $\text{H}{}^{\mathrm{+}}\text{NO}{}^{\mathrm{?}}{}_2$ for reduction to N₂O were 6.0–6.3, 4.02, 5.79 and 3.37, respectively. (2) With ascorbate/N,N,N′,N′-tetramethyl-p-phenylenediamine as exogenous substrate, addition of NO^?₂ or N₂O to an anaerobic cell suspension resulted in rapid alkalinization of the outer bulk medium. $\text{H}{}^{\mathrm{+}}\text{N}{}_2\text{O}$, $\text{H}{}^{\mathrm{+}}\text{NO}{}^{\mathrm{?}}{}_2$ for reduction to N₂ and $\text{H}{}^{\mathrm{+}}\text{NO}{}^{\mathrm{?}}{}_2$ for reduction to N₂O were ?0.84, ?2.33 and ?1.90, respectively. (3) The $\text{H}{}^{\mathrm{+}}\text{oxidant}$ ratios, mentioned in item 2, were not altered in the presence of $\text{valinomycin}\text{K}{}^{\mathrm{+}}$ and the triphenylmethylphosphonium cation. (4) A simplified scheme of electron transport to O₂, NO^?₂ and N₂O is presented which shows a periplasmic orientation of the nitrite reductase as well as the nitrous oxide reductase. Electrons destined for NO^?₂, N₂O or O₂ pass two H⁺-translocating sites. The $\text{H}{}^{\mathrm{+}}\text{electron}$ acceptor ratios predicted by this scheme are in good agreement with the experimental values.     

Occurrence of passive furosemide-sensitive transmembrane potassium transport in cultured cells

Furosemide ($\text{1 · 10}{}^{\mathrm{?4}}\text{M}$) inhibits a proportion of the total passive (ouabain-insensitive) K⁺ influx into primary chick heart cell cultures (85%), BC₃H1 cells (75%), MDCK cells (40%) and HeLa cells (57%). This action of furosemide upon K⁺ influx is independent of ($\text{Na}{}^{\mathrm{+}}\text{+}\text{K}{}^{\mathrm{+}}\text{)-}\text{pump}$ inhibition since the furosemide-sensitive component of the K⁺ influx is identical in the presence and absence of ouabain ($\text{1 · 10}{}^{\mathrm{?3}}\text{M}$). For HeLa cells the passive, furosemide-sensitive component of K⁺ influx is markedly dependent upon the external K⁺, Na⁺ and Cl^? content. Acetate, iodide and nitrate are ineffective as substitutes for Cl^?, whereas Br^? is partially effective. Partial Cl^? replacement by NO₃^? gave an apparent affinity of 100 mM [Cl]. Na⁺ replacement by choline⁺ abolishes the furosemide-sensitive component, whereas Li⁺ replacement reduces this component by 48%. Partial Na⁺ replacement by choline⁺ gives an apparent affinity of 25 mM [Na⁺]. Variation in the external K⁺ content gives an affinity for the furosemide-sensitive component of approx. 1.0 mM. Furosemide inhibition of the passive K⁺ inflúx is of high affinity, half-maximal inhibition being observed at $\text{5 · 10}{}^{\mathrm{?6}}\text{M}$ furosemide. Piretanide ($\text{1 · 10}{}^{\mathrm{?4}}\text{M}$) and phloretin ($\text{1 · 10}{}^{\mathrm{?4}}\text{M}$) inhibit the same component of passive K⁺ influx as furosemide; ethacrynic acid and amiloride ($\text{both}\text{1 · 10}{}^{\mathrm{?4}}\text{M}$) partially so. The stilbene, SITS ($\text{1 · 10}{}^{\mathrm{?6}}\text{M}$), was ineffective as an inhibitor of the furosemide-sensitive component.     

Photophosphorylation in bacterial chromatophores entrapped in alginate gel: Improvement of the physical and biochemical properties of gel beads with barium as gel-inducing agent

The immobilization of Rhodopseudomonas capsulata chromatophores by entrapment in an alginate gel is described. Alginate beads were prepared with Ba²⁺, Sr²⁺ and Ca²⁺ as gel-forming agents and compared for their mechanical strength, chemical resistance against disruption by phosphate-induced swelling, and yield of photophosphorylation activity. Barium alginate beads proved to have better physico-chemical properties than the more commonly used calcium alginate beads. After embedding in barium alginate gel, R. capsulata chromatophores retained a high yield (up to 70%) of their photophosphorylation capacity. Alginate entrapment did not cause a large increase in the Michaelis constant for ADP and phosphate, the substrates of adenosinetriphosphatase (ATPase). These constants were $\text{K}{}^{\mathrm{ADP}}{}_{\mathrm{<mtext>m</mtext>}}\text{= 1.4 × 10}{}^{\mathrm{?5}}\text{m}$ and $\text{K}{}^{\mathrm{P}}{}_{\mathrm{i}}{}_{\mathrm{<mtext>m</mtext>}}\text{= 2.2 × 10}{}^{\mathrm{?4}}\text{m}$ for free chromatophores and $\text{K}{}^{\mathrm{ADP}}{}_{\mathrm{<mtext>m</mtext>}}\text{= 2.3 × 10}{}^{\mathrm{?4}}\text{m}$ and $\text{K}{}^{\mathrm{P}}{}_{\mathrm{i}}{}_{\mathrm{<mtext>m</mtext>}}\text{= 5.6 × 10}{}^{\mathrm{?4}}\text{m}$ for chromatophores entrapped in barium alginate gel. However, embedding gave no additional protection against rapid inactivation of chromatophores upon storage at 3°C. Preliminary results with a batch reactor for continuous ATP regeneration are presented. The barium alginate method has two features which are not generally encountered at the same time, extremely mild conditions for entrapment and excellent physical properties of the gels beads, which make this method a suitable tool for the construction of bioreactors with immobilized cells or organelles.     

Molecular structure of collagen in solution: comparison of types I,II, III and V

Physical properties of pepsin-solubilized types I, II, III and V collagen have been measured in acid solution at 10°C. Our results indicate that types I, II and III collagen molecules undergo a monomer-aggregate equilibrium in solution whereas type V molecules appear to attract each other but do not undergo a similar monomer-aggregate equilibrium. Interstitial collagen monomers (I, II and III) have molecular weights between $\text{280 × 10}{}^3\text{and 289 × 10}{}^3$, translational diffusion coefficients between $\text{0.820 × 10}{}^{\mathrm{?7}}\text{and 0.845 × 10}{}^{\mathrm{?7}}\text{cm}{}^2\text{s}{}^{\mathrm{?1}}$ and particle scattering factors at an angle of 175.5° and wavelength of 633 nm between 0.430 and 0.460. Type V collagen molecules after pepsin digestion were found to have a higher molecular weight ($\text{307 × 10}{}^3$), similar translational diffusion coefficient ($\text{0.860 × 10}{}^{\mathrm{?7}}\text{cm}{}^2\text{s}{}^{\mathrm{?1}}$) and similar particle scattering factor at 175.5° (0.440) to the interstitial collagens. Theoretical bead models are discussed and suggest that changes in the translational diffusion coefficient were less sensitive to bending motions than were changes in the particle scattering factor at 175.5°C. Bend angles of 50° were shown to increase the particle scattering factor by 5% whereas a bend angle of greater than 125° was required to increase the translational diffusion coefficient by 5%. Models developed from idealized shapes seen by electron microscopy of rotary shadowed collagen molecules agreed best with experimental laser light scattering measurements when the bend angles were less than 90°.     

Carnitine uptake into human heart cells in culture

The uptake of radiolabeled carnitine and butyrobetaine has been studied in human heart cells (CCL 27). The uptake of carnitine is 3–10-fold higher in heart cells than in fibroblasts ($\text{pmol}\text{· μ}\text{g DNA}{}^{\mathrm{?1}}$). The uptake of carnitine increases with temperature coefficient $\text{K}{}_{\mathrm{<mtext>T</mtext>}}$ of 1.6 in the interval 10–20° C and with a negligible uptake at 4 and 10° C. The uptake of carnitine follows Michaelis-Menten kinetics with a $\text{K}{}_{\mathrm{<mtext>M</mtext>}}$ of $\text{4.8 ± 2.2 μ}\text{M}$ and $\text{V = 8.7 ± 3.2}\text{pmol}\text{· μ}\text{g DNA}{}^{\mathrm{?1}}\text{·}\text{h}{}^{\mathrm{?1}}$. Carnitine uptake is suppressed 90% by NaF (24 mM). Butyrobetaine is taken up into heart cells to the same extent as carnitine with a $\text{K}{}_{\mathrm{<mtext>M</mtext>}}$ of 5.7–17.3 μM and $\text{V = 8.7–9.3}\text{pmol}\text{· μ}\text{g DNA}{}^{\mathrm{?1}}\text{·}\text{h}{}^{\mathrm{?1}}$. Butyrobetaine inhibits competitively the uptake of carnitine and carnitine inhibits the uptake of butyrobetaine to the same extent. No conversion of radiolabeled butyrobetaine to carnitine, or carnitine to methyl choline was observed intra- or extracellulary during incubation. These data are compatible with a selective transport mechanism for carnitine which is also responsible for the uptake of butyrobetaine.