NaCl effects on 4-desmethylsterol composition of plasma-membrane-enriched preparations from citrus roots

Abstract The free 4-desmethylsterol composition of plasma-membrane-enriched preparations from white fibrous roots of Rangpur lime (Citrus reticulata var. austera hybrid?), Kharna khatta (C. kharna Raf.) and Etrog citron (C. medica L.) seedlings grown in the presence of 0, 50, or 100 mol m^?3 NaCl for 28 d was quantitated by gas chromatography (GC) on analytical capillary (SE-54 fused silica) columns and the sterols were identified by combined gas chromatography-mass spectrometry (GC-MS). Only three 4-desmethylsterols were positively identified by GC-MS, viz. campesterol, stigmasterol and sitosterol. Cholesterol could not be positively identified in any of the membrane preparations. Campesterol levels were generally similar for all treatments and for all three genotypes, approximating 30% of the total free 4-desmethylsterol content of the plasma membranes. At all levels of salinity (0, 50 or 100 mol m^?3 NaCl) sitosterol levels decreased in the order Rangpur lime > Kharna khatta > Etrog citron and stigmasterol levels decreased in the reverse order. The ratio of sitosterol to stigmasterol was highest in Rangpur lime and lowest in Etrog citron at each level of salinity and was reduced by salt treatment in all three genotypes. Salt-induced reductions in the ratio of ‘more planar’ to ‘less planar’ sterols correlated inversely with the accumulation of Cl^? in the leaves of the three genotypes suggesting a role for plasma membrane sterols in the Cl^? exclusion mechanism. A model relating sterol structure, membrane sterol composition and membrane permeability to Cl^? exclusion ability in citrus is presented.     

Zinc is a constituent of bovine heart cytochrome c oxidase preparations

Cytochrome c oxidase preparations from bovine heart muscle contain 1 zinc per 2 irons. Metal contents of nine preparations determined by inductively coupled plasma atomic emission spectrometry (ICP-AES) show that Cu, Fe and Zn are the only metals present in significant amounts with average Cu/Fe, Fe/Zn, and Cu/Zn atom ratios of 1.3, 2.1 and 2.8, respectively. Removal of adventitious copper results in a Cu:Fe:Zn stoichiometry of 2:2:1. The zinc is tightly bound. Dialysis against a solution of 1,10-phenanthroline at pH 7.4 or an acidic buffer (pH 4.4) does not remove Zn. Dialysis against 0.8 M KCN at pH 10 causes partial loss of both Cu and Zn. This is the first evidence for the presence of Zn in a cytochrome c oxidase.     

Effects of newly synthesised platinum(ii) complexes on mitochondrial functions

Protease deficient recA431 mutants of Escherichia coli are defective in their capacity for induction of SOS responses and were intermediate in their sensitivities to ultraviolet light (UV) and cis-platinum(II)diamminodichloride (cis-PDD). Survival after treatment determined as colony forming ability was greater in rec⁺ strains and decreased in recA13 mutants which are defective in both recA proteolytic and recombination capabilites. In contrast, recA431 mutants were as sensitive to N-methyl-N′-nitro-N-nitrosoguanidine (NTG) as the recA13 cells. When cells carried either the pKM101 or N3 plasmid, survival after treatment with the three mutagens was increased. Presence of these plasmids in cells also resulted in hypermutagenicity as indicated by reversion of the argE3 mutation using a modified Ames test. Mutagenesis by NTG and cis-PDD was increased, as was survival of cells treated with UV light, cis-PDD and NTG in both recA⁺ and recA431 (protease deficient) strains. No plasmid mediated enhancement of mutagenesis or cell survival was observed in recA13 mutants. Thus, the ability of the plasmids to enhance cell survival and mutagenesis was dependent on recombination proficiency of the recA gene product and not its regulatory proteolytic activity. Unlike UV or NTG, presence of one of these plasmids was needed to detect reversion of the argE3 mutation by cis-PDD.     

Characterization of a membrane-specific tubulin isoform by peptide mapping

A membrane-specific tubulin-like protein, found in preparations of synaptic plasma membranes and brain mitochondria, was analyzed by chemical and proteolytic peptide mapping to determine which part of the molecule was different from cytoplasmic tubulin. The membrane polypeptide was identical to alpha tubulin in the first two-thirds of the molecule containing the amino terminal, as found by peptide mapping. However, some differences were observed in the peptide maps of the carboxy terminal one third of the molecule which includes a domain that is important in the regulation of tubulin self-assembly.     

Dietary selenium status and plasma thyroid hormones in chicks

Experiments were conducted to study the effect of marginal levels of selenium and vitamin E on plasma thyroid hormones of meattype chicks. Plasma thyroxine (T₄) was significantly increased when a semipurified diet was supplemented with either selenium or vitamin E. Triiodothyronine (T₃) was also significantly increased by vitamin E and in one experiment with selenium supplementation. No significant increase in these hormones was observed in birds fed a corn-soybean-meal diet supplemented with these nutrients. Plasma corticosterone level was reduced and weight of the bursa of Fabricius increased by selenium or vitamin E supplementation. These nutrients may be necessary for providing the optimum thyroid conditions for activity of thyroid peroxidase.     

Selenium modifies carcinogen metabolism by inhibiting enzyme induction

Since selenium has been found to exert a protective action against carcinogenesis in various systems, the mechanism where-by sodium selenite inhibits DNA binding of the carcinogen, 7,12-dimethylbenz[a]anthracene, was investigated. It was found that selenite preferentially reduced DNA binding occurring through ananti-dihydrodiol epoxide metabolite of this carcinogen by inhibiting the induction of an enzyme system that generates this specific reactive metabolite.     

The hemolymph coagulation system in invertebrate animals

A hemocyte lysate from horseshoe crab produced a gel, when exposed to Gram-negative bacterial endotoxins. This gelation reaction of the lysate, so-called Limulus test, has been widely employed as a simple and very sensitive assay method for endotoxins. Recent biochemical studies on the principle of Limulus test indicate that the hemocytes contain several serine protease zymogens, which constitute a coagulation cascade triggered by endotoxins, and that there is a (1 3)--d-glucan-mediated coagulation pathway which also results in the formation of gel. Up to now, six protein components, designated coagulogen, proclotting enzyme, factor B, factor C, factor G and anti-LPS factor, all of which are closely associated with the endotoxin-mediated coagulation pathway, have been purified and biochemically characterized. Among these components, the complete amino acid sequences of coagulogens isolated from one American and three Asian species of horseshoe crabs have been established. Moreover, the reconstitution experiment using the isolated clotting factors, C, B, proclotting enzyme and coagulogen in the presence of endotoxin, leads to the formation of coagulin get. Based on these results, we propose here a mechanism for the Limulus coagulation cascade.     

Thermodynamic stability of proteins in salt solutions: A comparison of the effectiveness of protein stabilizers

The denaturation of proteins by guanidine hydrochloride was studied in the presence of different concentrations of stabilizing salts, namely potassium phosphate, ammonium sulfate, and potassium acetate. The denaturation transition was followed by observing changes in the peptide circular dichroism atpH 7.0 and 25°C. From these results the free energy of stabilization for the process native denatured was determined. It was found that the stabilizing power of the anions increased in the order acetate < sulfate < phosphate, in agreement with the anionic lyotropic series. Ribonuclease A, which is known to have a site that can bind either a phosphate or a sulfate ion, showed a larger stabilization by these anions than that for lysozyme, pepsinogen, and myoglobin.     

Biochemical and autoradiographic studies of TRH receptors in sections of rabbit spinal cord

Receptors for thyrotropin-releasing hormone (pGlu-His-Pro-NH2, TRH) on thaw-mounted sections of rabbit spinal cord have been identified biochemically and visualized by light microscopic autoradiography. Binding of [3H] [3-Me-His2]TRH to 20 microns sections exhibited high apparent affinity and a pharmacological specificity almost identical to that previously demonstrated for spinal TRH receptors in membranes. In autoradiograms, the highest density of TRH receptors appeared in the substantia gelatinosa of the dorsal gray and around the central canal, with intermediate levels in the ventral gray.