The modulation of membrane fluidity by hydrogenation processes. III. The hydrogenation of biomembranes of spinach chloroplasts and a study of the effect of this on photosynthetic electron transport

A method is reported for the in situ modification of the lipids of isolated spinach chloroplast membranes. The technique is based on a direct hydrogenation of the lipid double bonds in the presence of the catalyst, chlorotris(triphenylphosphine)rhodium (I). The pattern of hydrogenation achieved suggests that the catalyst distributes amongst all of the membranes. The polyunsaturated lipids within the membranes are hydrogenated at a faster rate and at an earlier stage than are the monoenoic lipids.Whilst addition of the catalyst to the chloroplast causes an initial 10–20% decrease in Hill activity, saturation of up to 40% of the double bonds present can be accomplished without causing further significant alterations in photosynthetic electron transport processes or marked morphological changes of the chloroplast structure as observed in the electron microscope.     

Serological detection of H-2K- and H-2D-gene products

Using the fluorescence-activated cell sorter (FACS II), we have analyzed the expression of H-2K- and H-2D-gene products on the membrane of various cellular components of the murine immune system. Using this serological technique we show a basic difference between T and B lymphocytes. Whereas all cellular components analyzed — hydrocortisone-resistant thymocytes, splenic T and B lymphocytes, macrophages and bone-marrow cells — expressed H-2K-subregion-encoded alloantigens at a high density, it seems that the high density expression of H-2D-encoded alloantigens is restricted mainly to B cells and to macrophages. Hydrocortisone-resistant thymocytes, splenic T lymphocytes and bone-marrow cells, on the other hand, showed significant expression of the H-2D alloantigens only at low membrane density. These results, then, provide evidence for the existence of an imbalance in serologically detectable expression of H-2K- and H-2D-region-gene products on the cell membrane of various cells comprising the murine immune system.Abbreviations usedin this paper DTH delayed type hypersensitivity - FCS fetal calf serum - FITC fluorescein isothiocyanate - HrT hydrocortisone-resistant thymocytes - Ig immunoglobulins P. De Baetselier is an EMBO and Euratom postdoctoral fellow     

Partial characterization of the plasma membrane ATPase from arho 0 petite strain ofSaccharomyces cerevisiae

Crude membrane preparations of arho ⁰ mutant ofSaccharomyces cerevisiae exhibit Mg²⁺-dependent ATPase activity. Over the optimal pH range, 5.0–6.75, the apparentV _max of the enzyme equals 590 nmoles of ATP hydrolyzed per minute per milligram protein, with an apparentK _m for ATP of 1.3 mM. ATP hydrolysis is insensitive to ouabain, venturicidin, aurovertin, and the protein inhibitor described by Pullman and Monroy; inhibited by oligomycin (at high concentrations) and sodium orthovandate, and it is sensitive to dicyclohexylcarbodiimide,p-hydroxymercuribenzoate, hydroxylamine, sodium fluoride, and sodium iodoacetate. The pH optimum and the inhibitor pattern distinguish the plasma membrane enzyme from the mitochondrial F₁ ATPase still present in these cells (this activity is sensitive to efrapeptin, aurovertin, and the protein inhibitor, but resistant to DCCD). In addition, the activity of the plasma membrane enzyme and its affinity for ATP are responsive to changes in the composition of the growth medium, with the highest activity observed in cells grown on methyl--d-glucoside, a sugar which results not only in partial release from catabolite repression but also requires the induction of an active transport system for growth.Author to whom correspondence should be addressed; recipient of a Research Career Award No. K06 05060 from the Institute of General Medical Sciences.     

Involvement of the cystathionine pathway in the biosynthesis of glutathione by isolated rat hepatocytes

The ability of l-methionine to support glutathione biosynthesis has been investigated in isolated rat hepatocytes under conditions of normal and depleted glutathione status. The addition of l-[³⁵S]methionine or [l-[³⁵S]homocysteine to incubation media containing hepatocytes results in the incorporation of ³⁵S into intracellular glutathione. Additionally both l-methionine and l-homocysteine are capable of supporting the resynthesis of glutathione in isolated hepatocytes after prior depletion with diethyl maleate. The inclusion in the incubation medium of 1 mm propargylglycine, which is an irreversible inhibitor of the terminal enzyme of the cystathionine pathway, substantially blocks the incorporation of ³⁵S from methionine and l-homocysteine into cellular glutathione. Propargylglycine treatment of hepatocytes in the presence of [³⁵S]methionine is shown to result in the intracellular accumulation of [³⁵S]cystathionine. These results strongly support the conclusion that in rat hepatocytes the cystathionine pathway enables methionine to provide a significant source of l-cysteine for the support of glutathione biosynthesis, under both normal and glutathione-depleted conditions.     

Kinetin-promoted transport of assimilates in stems of Phaseolus vulgaris L.

Kinetin, applied as a dispersion in aqueous lanolin to the stumps of decapitated stems of P. vulgaris plants with their roots removed, was found to promote the transport of ¹⁴C- and ³²P-labelled assimilates to the site of hormone application. Measurement of photosynthetic rate of, and assimilate export rate from the source leaves, indicated that kinetin was not acting to promote assimilate transport by stimulating these processes. Moreover, it was found that the time between kinetin application and detection of an enhanced transport flux was independent of the distance over which kinetin would need to move to be present throughout the length of the transport pathway. These observations, together with the finding that lateral applications of kinetin to the stems resulted in an enhanced localized accumulation of assimilates, provided evidence that kinetin acted locally at its point of application to stimulate assimilate transfer.Abbreviations GA₃ gibberellic acid - IAA indol-3yl-acetic acid     

An assessment of auxin-promoted transport in decapitated stems and whole shoots of Phaseolus vulgaris L.

¹⁴C-photosynthate transfer in decapitated stems of P. vulgaris plants, treated with IAA (indol-3yl-acetic acid), appeared, as ascertained by microautoradiography, to be restricted to cells of sieve-element appearance. The IAA-induced promotion of photosynthate transport was found not to depend on any artifacts caused by the decapitation procedure. Rather, decapitation primarily served the purpose of removing photosynthate sources above the point of hormone application which otherwise suppressed the expression of the IAA effect on acropetal photosynthate transport. Furthermore, by manipulating stem levels of endogenous auxins with the inhibitor of polar auxin transport, 1-(2¹-carboxyphenyl)-3-phenylpropane-1,3-dione (ACP1.55), evidence was obtained indicating that photosynthate transfer to the shoot apex depended, at least in part, on endogenous levels of auxins at site(s) remote from the apical sink (i.e. shoot apex).Abbreviations ACP1.55 1-(2¹-carboxyphenyl)-3-phenylpropane-1,3-dione - DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea - IAA indol-3yl-acetic acid     

Gibberellic-acid-promoted transport of assimilates in stems of Phaseolus vulgaris L.

Gibberellic acid (GA₃), applied as a dispersion in aqueous lanolin to the stumps of decapitated stems of P. vulgaris plants, was found to promote the transfer of ¹⁴C-and ³²P-labelled assimilates to the site of hormone application. Measurements of the component transfer processes, operating between source and sink (site of hormone application), showed that GA₃ was not acting to promote assimilate transfer by increasing the photosynthetic rate of, or the assimilate export rate from the source, nor by altering the mobilizing ability of the competing root sink. Here, it also was found that the time between GA₃ application and detection of an enhanced transport flux was independent of the length of the transport pathway. Overall, the evidence obtained indicated that GA₃ was not acting on any transfer process remote from its point of hormone application but was acting locally at this latter point.Abbreviations GA₃ gibberellic acid - IAA indol-3yl-acetic acid     

Ligninolytic activity of Phanerochaete chrysosporium: Physiology of suppression by NH 4 + and l-glutamate

Previous research showed that addition of nutrient nitrogen to ligninolytic (stationary, nitrogen-starved) cultures of the wood-decomposing basidiomycete Phanerochaete chrysosporium causes a suppression of lignin degradation. The present study examined early effects on nitrogen metabolism that followed addition of NH ₄ ⁺ and l-glutamate at concentrations that yield similar patterns of suppression. Both nitrogenous compounds were rapidly assimilated (>80% in 6 h). Both caused an initial 80% or greater increase in the intracellular glutamate pool and had similar effects in increasing the specific activities of NADP- and NAD-glutamate dehydrogenases and glutamine synthetase. Differences between the effects of added NH ₄ ⁺ and glutamate showed that suppression was not correlated with intracellular pools of arginine or glutamine, nor was the maintenance of an elevated glutamate pool required to maintain the suppressed state. While a portion of the initial glutamate suppression could be attributed to an effect on central carbon metabolism through glutamate catabolism by NAD-glutamate dehydrogenase, the long term suppression by glutamate and the suppression by NH ₄ ⁺ were more specific. Suppression by NH ₄ ⁺ or glutamate in the presence or absence of protein synthesis (cycloheximide) followed essentially identical kinetics during 12 h. These results indicate that nitrogen additions cause a biochemical repression of enzymes associated with lignin degradation. Results are consistent with the hypothesis that nitrogen metabolism via glutamate plays a role in initiation of repression.Non-Standard Abbreviations DMS 2,2-dimethylsuccinate - TCA trichloroacetic acid     

Hemotypes and genetic structure of Camargue horses

The nature and distribution of hemotypes constituted by electrophoretic phenotypes in six loci, in a group of 183 Camargue horses, have been compared with those of five breeds of horses and ponies. The genetic similarities have been observed mainly with New Forest and Haflinger ponies, less with Barbs and Thoroughbreds, and the least with Arab horses.     

Serratia species isolated from plants

Using the selective caprylate-thallous agar medium, the presence ofSerratia species was systematically examined in 623 plant samples. A total of 167Serratia strains was isolated from these plant samples and identified to species and biogroups. Uniform and characteristicSerratia populations were found in figs and coconuts: (i)Serratia ficaria was recovered from most figs collected in California, Tunisia, and France; various biotypes ofS. marcescens also were found in figs; (ii) onlyS. marinorubra was recovered from coconuts bought on two continents. From plants other than figs and coconuts, representatives were isolated of all eightSerratia species we presently recognize—with a large preponderance ofS. liquefaciens andS. proteamaculans. These other plant samples fell into threeSerratia-prevalence groups: (i) vegetables-mushrooms-mosses-decaying plant material (53.8% of these samples were positive forSerratia); (ii) grasses (23.7% positive); and (iii) trees and shrubs-small plants (8.4% positive). PigmentedS. marcescens biotypes were rarely isolated from plants (except from figs). Of theS. marcescens biogroups most frequently encountered in nosocomial and iatrogenic infections of man, A3 and A4 were isolated from plants in this study, but A5/8 and TCT were not.