The effect of hydroxyurea on the death resulting from biotin starvation was examined. This chemical, which preferentially inhibits deoxyribonucleic acid (DNA) replication in the yeast Saccharomyces cerevisiae, prevented death after biotin starvation. Hydroxyurea also inhibits DNA synthesis. Growth, ribonucleic acid (RNA) synthesis, and protein synthesis were less sensitive to this chemical. Cell death was strongly suppressed on addition of 0.2M hydroxyurea when the cells were simultaneously starved for biotin. At this concentration, DNA synthesis was selectively inhibited, while RNA and protein syntheses continued at nearly the control rate for 8hr of cultivation. In the subculture from which hydroxyurea was removed after 8hr of growth, DNA synthesis was resumed abruptly and cell death occurred without any lag. Furthermore, as the timing of addition of hydroxyurea into the biotin-free medium containing aspartic acid (Asp medium) was delayed, the rate of cell death increased proportionally. On the other hand, when hydroxyurea was added at 0.2M to the Asp medium, cells underwent one cycle of budding, but neither the nucleus nor the cell divided. In the presence of hydroxyurea at 0.2M, the incorporation of acetate [U-14C] into the lipid fraction of the cells was almost the same as the control without hydroxyurea even after 8hr of cultivation. These results indicate that death resulting from unbalanced growth did not occur when DNA synthesis was inhibited, even though macromolecular substances and buds were normally produced under the biotin-deficient condition.
The acetamidase of Brevibacterium R312, a strain with nitrilase activity, has very different characteristics from those of its acetonitrilase. This acetamidase presents an activity for pH values greater than 3 and has an optimum activity at pH 7. The optimal temperature is between 60° and 70°. The enzyme resists high temperatures and its Michaelis constant is 3.5×10-3M. The -SH, -OH, -NH2, -NH-C-NH2, and tryptophan NH groups seem to be necessary for the acetamidase activity. The enzyme remains in supernatant fluid from the centrifugation at 180, 000×g. It is an adaptative enzyme. This acetamidase looks like aliphatic amidases described by other authors.
The isolation and characterization of 7 strains of bacteria from various sources, which utilized benzylpenicillin as carbon and nitrogen sources are described. The isolates were all gram-negative rods with polar flagella exhibiting oxidative metabolism. Five isolates were identified as members of the group of fluorescent pseudomonads. During growth on benzylpenicillin, benzylpenicilloic acid and benzylpenilloic acid accumulated. 6-Aminopenicillanic acid was not demonstrated.
The isoenzyme patterns of several hydrolytic enzymes, viz., acid phosphatase, alkaline phosphatase, and catalase, in virulent and avirulent, agrocin-resistant Agrobacterium tumefaciens have been studied. Agrocin resistance brought about genetic repression in regard to the synthesis of one of the isoenzymes in each of these three enzymes. Avirulent resistant strains also showed a reduction in the activities of all the hydrolases. Although Mg2+ stimulated the activity of alkaline phosphatase, no absolute requirement of any metal ions for the activity of the enzyme was observed.