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Phospho-MurNAc-pentapeptide translocase activity in the membrane of M. luteus was lost upon addition of the detergent, Triton X-100, but could be restored by addition of lipid fractions to the assay. By assay in the presence of lipid, the activity of the Triton-solubilized enzyme could be measured. The synthesis of C(55)-isoprenyl-P-P-MurNAc-pentapeptide from UDP-MurNAc-pentapeptide required C(55)-isoprenyl-P, and was stimulated by a neutral lipid. The exchange reaction of UDP-MurNAc-pentapeptide with UMP required a polar lipid fraction, but the reaction was not affected by C(55)-isoprenyl-P or the neutral lipid. Thus, measurement of activity of the detergent-solubilized enzyme requires addition of three lipids, the lipid substrate (C(55)-isoprenyl-P), the neutral lipid, and a polar lipid.

Okazaki, Tuneko (Washington University School of Medicine, St. Louis, Mo.), Jack L. Stominger, and Reiji Okazaki. Thymidine diphosphate-l-rhamnose metabolism in smooth and rough strains of Escherichia coli and Salmonella weslaco. J. Bacteriol. 86:118-124. 1963.-Logarithmic-phase cells of Escherichia coli O18, which have rhamnose in their lipopolysaccharide, contained only traces of thymidine diphosphate (TDP)-l-rhamnose. Extracts of this organism, however, catalyzed the synthesis of TDP-l-rhamnose from TDP-d-glucose. On the other hand, cells of E. coli R44, a rough variant of this strain which contains no rhamnose in its lipopolysaccharide, contained a large amount of TDP-l-rhamnose. Like the smooth form, this organism was able to synthesize TDP-l-rhamnose. The rough variant is apparently a mutant blocked in some manner in utilization of TDP-l-rhamnose for lipopolysaccharide synthesis. Similar studies of smooth (rhamnose-containing) and rough (rhamnose-lacking) forms of Salmonella weslaco showed that both organisms can synthesize TDP-l-rhamnose from TDP-d-glucose. In contrast to the smooth and rough forms of E. coli O18, only traces of TDP-l-rhamnose were detected in extracts of both forms. A second thymidine diphosphosugar compound isolated from E. coli R44 is similar or identical to TDP-X, previously isolated from E. coli Y-10.

The role of nucleotides as "carriers" of small molecules for biosynthetic reactions is discussed. Following this introduction, the particular problem of nucleotide intermediates in chondroitin sulfate synthesis is presented. The egg shell of the hen contains a form of chondroitin sulfate and particular emphasis is placed on the biosynthesis of sulfated polysaccharides in the hen oviduct, which has been studied in the author's laboratory.

HL-A 2 and HL-A 7 antigens have been solubilized from cultured human lymphocytes by papain and purified on a small radioactive scale after formation of immune complexes, or on a large scale by column chromatographic methods. In both cases, it has been shown that the materials obtained consist of two noncovalently bound fragments. One fragment is a glycopeptide of molecular weight 30,000-31,000, the other is a peptide of molecular weight 11,000-12,000. In polyacrylamide gels containing 8 M urea, the large fragments of HL-A 2 and HL-A 7 exhibited different electrophoretic mobilities, while the small fragments were the same. The relationship of these materials to the native HL-A molecule is discussed.

Bacitracin is an inhibitor of the biosynthesis of squalene and sterols from mevalonic acid, C(5)-isopentenyl pyrophosphate, or C(15)-farnesyl pyrophosphate catalyzed by preparations from rat liver. The antibiotic is active at extremely low ratios of antibiotic to substrate. The mechanism of inhibition appears to be the formation of a complex between bacitracin, divalent cation, and C(15)-farnesyl pyrophosphate and other isoprenyl pyrophosphates. It is similar to the formation of the complex with C(55)-isopropenyl pyrophosphate in microbial systems. The toxicity of bacitracin for animal cells could be due in part to the formation of these complexes.

The removal by papain of a histocompatibility antigen, HL-A 2, from the surface of intact peripheral blood lymphocytes has been examined. Up to 80% of the antigenic determinant can be removed within 90 minutes. If the cells are reincubated in nutritive medium, re-expression of HL-A 2 is complete within 6 hours. Re-expression is reversibly inhibited by puromycin (50 mug/ml), but actinomycin D (6 mug/ml) only partially inhibited re-expression after 2 hours of prior incubation with the drug.