Substructure in rod photoreceptor membranes

Frog retinae, fixed only in buffered glutaraldehyde, were embedded for sectioning in glutaraldehyde polymerized with urea. In suitably thin sections globular substructures were seen in negative contrast after ionic staining with uranyl acetate and lead citrate, or after staining with neutralized phosphotungstic acid. Efforts to extract at least some of the lipid from sections before ionic staining enhanced the visualization of the "globules". Exposure to KMnO4 solution, used as an oxidative section stain, also outlined globular substructure in negative contrast, but with the additional feature that positively stained surface "leaflets" associated with the aqueous compartment were well defined. Staining sections with OSO4 vapor resulted in positively stained membranes, but without any evident substructure. However, when sections which previously had been exposed to OSO4 vapor were secondarily stained with uranyl acetate and/or lead citrate, positively stained globular substructures then were revealed. The globular substructures always were centered in the hydrophobic core region of the disc membranes, and symmetrically spanned the full thickness of this layer. The diameter of individual particles approximated 50-55 A. Reasons are presented for the supposition that the evident globules incorporate at least hydrophobic components of rhodopsin molecules. Findings are discussed in relation to various models of disc membrane organization that have been proposed in recent years.

Fluorometric assay of thioguanine

A spectrophotofluorometric method is described for the assay of thioguanine. The assay involves the oxidation of thioguanine with potassium permanganate to a fluorescent product. The method is suitable for routine quality control in laboratory preparations of thioguanine.

Oxidation of lipids and membranes I: in vitro formation of peroxidative lipid polymers

Fluorescent polymers were obtained by oxidizing partly emulsified linolenic acid with different oxidants. The speed of formation of polymers differed for the various oxidants, and the difference was not a simple function of the oxidation potential. The speed of polymerization also depended on the nature of the emulsion. The presence of egg albumen in the emulsion enhanced polymer formation with all oxidants. When the oxidants used are arranged in the order of decreasing speed of polymer formation, the order is different in the presence of albumen from what it is in the absence of albumen. With different oxidation catalysts most antioxidants and amino acids tested enhanced polymerization. In oxidation with ferric ions, with K-dichromate, and without added oxidants the only antioxidants which delayed polymerization were "inhibitors." "Retarders" enhanced polymerization. With KMnO4 slight delay was caused by some retarders. The findings indicate that not only oxidation catalysts, but also proteins, amino acids, and antioxidants enhance polymerization. The possibility is suggested that in animal cells lipid pigment formation might represent a mechanism for neutralizing free radicals.

Studies on chemical modification of thionucleosides in the transfer ribonucleic acid of Escherichia coli

(35)S-labelled tRNA from Escherichia coli was treated with chemical reagents such as CNBr, H(2)O(2), NH(2)OH, I(2), HNO(2), KMnO(4) and NaIO(4), under mild conditions where the four major bases were not affected. Gel filtration of the treated tRNA showed desulphurization to various extents, depending on the nature of the reagent. The treated samples after conversion into nucleosides were chromatographed on a phosphocellulose column. NH(2)OH, I(2) and NaIO(4) reacted with all the four thionucleosides of E. coli tRNA, 4-thiouridine (s(4)U), 5-methylaminomethyl-2-thiouridine (mnm(5)s(2)U), 2-thiocytidine (s(2)C) and 2-methylthio-N(6)-isopentenyladenosine (ms(2)i(6)A), to various extents. CNBr, HNO(2) and NaHSO(3) reacted with s(4)U, mnm(5)s(2)U and s(2)C, but not with ms(2)i(6)A. KMnO(4) and H(2)O(2) were also found to react extensively with thionucleosides in tRNA. Iodine oxidation of (35)S-labelled tRNA showed that only 6% of the sulphur was involved in disulphide formation. Desulphurization of E. coli tRNA with CNBr resulted in marked loss of acceptor activities for glutamic acid, glutamine and lysine. Acceptor activities for alanine, arginine, glycine, isoleucine, methionine, phenylalanine, serine, tyrosine and valine were also affected, but to a lesser extent. Five other amino acids tested were almost unaffected. These results indicate the fate of thionucleosides in tRNA when subjected to various chemical reactions and the involvement of sulphur in aminoacyl-tRNA synthetase recognition of some tRNA species of E. coli.

A method for determination of saturated phosphatidylcholine

Phosphatidylcholine preparations containing saturated and unsaturated molecular species were subjected to KMnO(4)-NaIO(4) oxidation in aqueous acetic acid, which left only disaturated species intact. After the oxidation, the remaining intact phosphatidylcholine was separated by thin-layer chromatography. The procedure could be used as a simple and rapid method for microdetermination of the saturated species in phosphatidylcholine preparations containing more than 0.1 micro mole of the saturated species. The contents of the saturated species in native phosphatidylcholines obtained from rat lung tissue and washings by this procedure were 35.7% and 58.3%, respectively.

Proteinaceous hexagonal inclusions in hyphae of Whetzelinia sclerotiorum and Neurospora crassa

The chemical nature of the hexagonal inclusions occurring in microbodies of Whetzelinia sclerotiorum and in the cytoplasm of Neurospora crassa was investigated. These inclusions were considered to be ergosterol or protein. The major β-3-hydroxyl-sterol present in W. sclerotiorum was identified as ergosterol. When glutaraldehyde (GA) fixed hyphae of both W. sclerotiorum and N. crassa were treated with sterol-extracting solvents, the hexagonal inclusions were still observed in thin sections. Sodium methoxide treatment of thin sections of hyphae fixed with GA and OsO4 removed the lipid bodies, but not the hexagonal inclusions. Various proteases, subtilisin, Sigma protease type VI, and pepsin, digested the inclusions from thin sections of hyphae fixed only with GA. Inclusions in thin sections of hyphae fixed with 2% KMnO4 were extracted by 1.0 N NH4OH, 0.1 M Na3PO4, or 0.16 N NaOH (about pH 12), but not by 0.16 N NaOH adjusted to pH 8.8 with HCl. These results indicate that the hexagonal inclusions in W. sclerotiorum and N. crassa are primarily proteinaceous in nature and are similar in composition to the Woronin bodies observed in other Ascomycetes.

Effects of concentration of volatile metabolites from bacteria and germinating seeds on fungi in the presence of selective absorbents

Fusarium oxysporum f. conglutinans, Gelasinospora cerealis, Penicillium viridicatum, Trichoderma viride, and Zygorhynchus vuilleminii were grown on slide cultures supported above cultures of seven bacteria and one actinomycete. Except with Escherichia coli and Nocardia corallina, heavy bacterial growth always inhibited growth and sporulation of the fungi, whereas lighter growth either inhibited, did not alter, or stimulated growth and (or) sporulation, depending on the fungus–bacterium combination. Differential absorption of the volatiles by KOH, KMnO4, charcoal, or soil indicated that different volatiles were produced, that some were inhibitory and others stimulatory, and that at least some of the volatiles were organic. Volatiles emitted by germinating seeds reduced spore formation only in G. cerealis, Penicillium vermiculatum, and Z. vuilleminii, but otherwise had no effect on growth, sporulation, or morphology of the above fungi nor on Aspergillus flavipes or Cunninghamella elegans.