Batch culture of in L-mandelate- or phenylgly-oxylate-salts medium showed an unusual non-exponential pattern unless the inoculum had been grown on benzyl alcohol. There were transient accumulations of benzaldehyde and benzyl alcohol caused by the limitation of L-mandelate oxidation by low activities of benzaldehyde dehydrogenase and the diversion of reducing power to the formation of benzyl alcohol. enzymic activities were estimated from patterns of substrate utilization in batch cultures containing pairs of substrates. When bacteria previously grown in L-mandelate-salts medium were inoculated into media containing L-mandelate and a second carbon source, metabolism of L-mandelate was arithmetical in the presence of benzoate, catechol or succinate, but accelerated on exhaustion of the second substrate. This indicated repression of the enzymes involved in L-mandelate oxidation. Inoculation of bacteria grown in benzoate-salts medium into medium containing L-mandelate and benzoate gave diauxie with initial utilization of benzoate. Similar experiments showed that benzoate oxidation was not repressed by catechol and only partially repressed by succinate. Measurement of L-mandelate dehydrogenase, phenylgly-oxylate carboxy-lyase and benzaldehyde dehydrogenase I in bacterial extracts showed no evidence for feedback inhibition by intermediates of the pathway. The rates of L-mandelate and benzoate utilization by bacterial suspensions were inhibited by succinate and catechol but not by other intermediates of the pathway.


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