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W L McLellan

Publications and source records attributed to W L McLellan.

11 recordsLinked to original sources
PubMed1976

Analysis of the envelope of Rauscher murine oncornavirus: in vitro labeling of glycopeptides.

The identity and localization of the oligosaccharides of Rauscher murine type C viral glycoproteins have been examined by techniques of in vitro labeling. Terminal sialic acid was labeled with tritium by borohydride reduction after selective periodate oxidation, and galactose was labeled by borohydride reduction after specific enzymatic oxidation of the nonreducing terminal of the sugar. The results were compared with those of protein surface labeling with pyridoxal phosphate or lactoperoxidase catalyzed radioiodination. Examination of the labeled reaction products by polyacrylamide gel electrophoresis in sodium dodecyl sulfate showed that in every case the major component labeled was a glycoprotein of about 70,000 daltons. The identity of this glycoprotein as the virion envelope component was confirmed by immunoprecipitation with mono-specific antiserum prepared against purified Rauscher virus glycopeptides of 69,000 and 71,000 daltons. No other protein or glycoprotein on the surface of the virion was detected, and disruption of virions-before labeling did not reveal additional distinctive glycoproteins. There was minor labeling of sugar residues of other components, but these remain to be characterized and are not now identified as other viral proteins. Studies of the structural organization of virion proteins using the cross-linking reagent methyl-4-mercaptobutyrimidate showed only linkage of the virion envelope or core proteins to themselves. These results indicate that most, if not all, of the oligosaccharides at the surface of Rauscher virus are entities of the 69,000- and 71,000-dalton glycopeptides and that they contain a terminal sialic acid and galactose and a subterminal galactose.

Galactose↗
PubMed1970

Translational repression in the arginine system of Escherichia coli.

Translation of bacterial mRNA, divorced from transcription, has been obtained for enzymes of arginine synthesis; evidence has been acquired for repression by arginine at the level of translation. mRNAs for acetylornithinase and ornithine transcarbamylase were accumulated by arginine starvation of argR(+) and argR(-) arginine auxotrophs derived from Escherichia coli K12. Further transcription was inhibited with rifampicin or miracil D, and enzyme formation was measured in the presence of either an excess of, or a restricted supply of, arginine. For the argR(+) strain 961, little mRNA was found without starvation; for the argR(-) strain 977, a considerable amount of mRNA was demonstrated even without starvation. There was relatively little translation for the argR(+) strain, but not for the argR(-) strain, in the presence of excess arginine, apparently due to an accelerated degradation of mRNA in the argR(+) strain under repressive conditions.

Amidohydrolases↗
PubMed1970

Purification of phosphomannanase and its action on the yeast cell wall.

An improved assay for phosphomannanase (an enzyme required for the preparation of yeast protoplasts) has been developed based on the release of mannan from yeast cell walls. A procedure for the growth of Bacillus circulans on a large scale for maximal production of the enzyme is described. The culture medium containing the secreted enzyme was concentrated, and the enzyme was purified by protamine sulfate treatment, ammonium sulfate fractionation, gel filtration on P-100, and isoelectric density gradient electrophoresis. Although the enzyme was purified to apparent homogeneity, it still contained laminarinase activity which could not be separated by size or charge. The two enzymatic activities also exhibited two isoelectric points (pH 5.9 and 6.8) on ampholine electrophoresis. The laminarinase was not active on yeast glucan. The enzyme preparation was shown to remove mannan from yeast without removing glucan. Electron microscopic observation supports the idea that this mannan is the outer layer of the yeast wall. Phosphomannanase will produce protoplasts from yeast when supplemented with relatively low amounts of snail enzyme. This activity is present in snail enzyme but appeares to be rate-limiting when snail enzyme alone is used. Phosphomannanase has proven useful for studying the macromolecular organization of polymers in the yeast cell wall.

Bacillus↗
PubMed1968

Phosphomannanase (PR-factor), an enzyme required for the formation of yeast protoplasts.

The PR-factor, an enzyme necessary for the production of protoplasts from yeast, was identified and was named phosphomannanase. The enzyme released mannan and mannan-proteins from yeasts harvested in the logarithmic phase of growth. The size of the molecules released was greater than 200,000 daltons, which indicated that the enzyme splits very few bonds of the yeast wall. The PR-factor also depolymerized phosphomannans produced by the Hansenula species. The degradation of these substances was due to the splitting of mannosidic bonds. However, the phosphodiester bonds present in these phosphomannans were involved in the specificity of the enzyme, and the number of mannosidic bonds cleaved was dependent on the number of phosphodiester bonds present. We studied the products of degradation of Hansenula phosphomannans and were unable to identify the exact bond split by the enzyme. After enzymatic digestion and subsequent splitting of phosphodiester bonds, phosphomannan Y-2448 yielded products too complex to be separated. Phosphomannan Y-1842 was shown to have a structure more complex than that previously proposed. The action of the enzyme on the phosphate-rich walls of Saccharomyces was studied. Mannan, containing intact phosphodiester bonds, was released from the walls. Mild acid hydrolysis of this released material split the diester bonds to yield monosaccharide and polysaccharide terminated in mannose-6-phosphate. From these products, we deduced that the enzyme cleaved a mannosidic bond adjacent to a mannose, which is also phosphodiester linked through carbon 1. The significance of phosphodiester bonds in the attachment of mannan and mannan-protein enzymes to the wall of yeast is discussed.

Bacillus↗