Summary: It was established that grew rapidly in a simple medium containing yeast extract (0.2 %, w/v) plus glucose (2 %, w/v). These cultures were in or near to a state of nitrogen limitation and the concentration of secreted aspartate proteinase increased rapidly (within 3-4 h) on addition of BSA. Synthesis and secretion were apparently controlled both positively (induction by albumin or, more probably, the peptides produced from it) and negatively (repression by NHCl). A small intracellular pool of the enzyme was detected during production of the enzyme and this pool decreased with the cessation of synthesis and secretion. A stable mutant, IR24, was isolated which secreted less than 0.3% of the amount of the proteinase exported by the parent strain ATCC 10261. The LD values for mutant IR24 and the parent strain administered intravenously to mice were > 1.0 x 10 and 1.6 x 10 c.f.u. kg respectively.


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