1. The biosynthesis of the wall teichoic acid in Staphylococcus lactis I3 was studied. Cell-free particulate enzyme preparations, probably representing fragmented membrane, were isolated and used for the synthesis of polymer. 2. By using appropriately labelled CDP-glycerol and UDP-N-acetylglucosamine it was shown that the former contributes a glycerol phosphate residue and the latter contributes an N-acetylglucosamine 1-phosphate residue to the repeating unit. 3. No polymer was synthesized unless both nucleotides were present, and no other substrates were required. 4. The properties of the enzyme system were studied. 5. Although attempts to fractionate the system failed, the biosynthesis is believed to be complex and its mechanism is considered.
Although the structure of streptomycin has been known for some time, the process of its biosynthesis by Streptomyce8 gri8eua has not yet been elucidated. Blumsom & Baddiley (1961) examined extracts of S. gri8eU8 for nucleotide-sugar compounds which may be involved in synthesis of the streptose and N-methyl-L-glucosamine moieties of streptomycin. They found thymidine diphosphate rhamnose a possible intermediate for streptose, but no compounds more closely related to streptomycin were identified. Other workers have grown S. gri8eu8 in the presence of labelled compounds and examined the incorporation of the isotope into the streptomycin produced. Such experiments were first carried out by Karow, Peck, Rosenblum & Wood
1. Several peptides containing either of the sequences -Phe(NO2)-Trp- and -Phe(NO2)-Phe- and an uncharged hydrophilic group were synthesized, and the steady-state kinetics of their hydrolysis by pig pepsin (EC 3.4.23.1) and chicken liver cathepsin D (EC 3.4.23.5) were determined. Despite the presence of a hydrophilic group to increase substrate solubility, it was not possible to achieve the condition [S]0 much greater than Km, and, in some cases, only values of kcat./Km could be determined by measuring the first-order rate constant when [S]0 much less than Km. 2. Occupancy of the P2 and P3 sites considerably enhanced the specificity constant, and alanine was more effective than glycine at site P2. 3. The specificity constants for the hydrolysis by pepsin of those substrates in the present series that contain an amino acid residue at site P3 are considerably lower than for comparable substrates containing a cationic group. This difference does not apply to cathepsin D. 4. Hydrolyses with cathepsin D commonly exhibited a lag phase, and a possible explanation for this is given.
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