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.     

An in vitro comparison of Trypanosoma spp. (subgenus Schizotrypanum) from bats

Summary Epimastigotes of Trypanosoma vespertilionis from diphasic blood agar cultures were on the average longer and the distance between the nucleus and kinetoplast greater than epimastigotes of T. hedricki, T. myoti and T. dionisii. Also, no yellow granules were seen in the epimastigotes of T. vespertilionis whereas they were obvious in the other three species. Long thin trypomastigotes which are characteristic of T. hedricki, T. myoti and T. dionisii cultures were not seen in T. vespertilionis. T. dionisii was much less infective to fibroblasts from mice and did not develop in fibroblasts from chicken, as did T. hedricki and T. myoti. Blood trypomastigotes were seen in chicken embryos inoculated with blood agar cultures of T. hedricki and T. myoti, but none was seen in embryos infected with T. dionisii.The cultural characteristics examined could not be used to differentiate T. hedricki from T. myoti. ac]19810317     

The measurement of the intrinsic alkaline Bohr effect of various human haemoglobins by isoelectric focusing

We have used isoelectric focusing to measure the differences between the pI values of various normal and mutant human haemoglobins when completely deoxygenated and when fully liganded with CO. It was assumed that the ΔpI(deox.–ox.) values might correspond quantitatively to the intrinsic alkaline Bohr effect, as most of the anionic cofactors of the haemoglobin molecule are `stripped' off during the electrophoretic process. In haemoglobins known to exhibit a normal Bohr coefficient (ΔlogP₅₀/ΔpH) in solutions, the ΔpI(deox.–ox.) values are lower the higher their respective pI(ox.) values. This indicates that for any particular haemoglobin the ΔpI(deox.–ox.) value accounts for the difference in surface charges at the pH of its pI value. This was confirmed by measuring, by the direct-titration technique, the difference in pH of deoxy and fully liganded haemoglobin A₀ (α₂β₂) solutions in conditions approximating those of the isoelectric focusing, i.e. at 5°C and very low concentration of KCl. The variation of the ΔpH(deox.–ox.) curve as a function of pH (ox.) was similar to the isoelectric-focusing curve relating the variation of ΔpI(deox.–ox.) versus pI(ox.) in various haemoglobins with Bohr factor identical with that of haemoglobin A₀. In haemoglobin A₀ the ΔpI(deox.–ox.) value is 0.17 pH unit, which corresponds to a difference of 1.20 positive charges between the oxy and deoxy states of the tetrameric haemoglobin. This value compares favourably with the values of the intrinsic Bohr effect estimated in back-titration experiments. The ΔpI(deox.–ox.) values of mutant or chemically modified haemoglobins carrying an abnormality at the N- or C-terminus of the α-chains are decreased by 30% compared with the ΔpI value measured in haemoglobin A₀. When the C-terminus of the β-chains is altered, as in Hb Nancy (α₂β^{Tyr-145→Asp}₂), we observed a 70% decrease in the ΔpI value compared with that measured in haemoglobin A₀. These values are in close agreement with the estimated respective roles of the two major Bohr groups, Val-1α and His-146β, at the origin of the intrinsic alkaline Bohr effect [Kilmartin, Fogg, Luzzana & Rossi-Bernardi (1973) J. Biol. Chem. 248, 7039–7043; Perutz, Kilmartin, Nishikura, Fogg, Butler & Rollema (1980) J. Mol. Biol. 138, 649–670]. In other mutant haemoglobins it is demonstrated also that the ΔpI(deox.–ox.) value may be decreased or even suppressed when the substitution affects residues involved in the stability of the tetramer. These results support the interpretation proposed by Perutz, Kilmartin, Nishikura, Fogg, Butler & Rollema [(1980), J. Mol. Biol. 138, 649–670] for the mechanism of the alkaline Bohr effect, and also indicate that the transition between the two quaternary configurations is a prerequisite for the full expression of the alkaline Bohr effect.