Acylation of 6-Aminopenicillanic Acid by Penicillium chrysogenum.

num deacylated phenoxymethylpenicillin about six times faster than benzylpenicillin to 6-aminopenicillanic acid (6-APA) (R. C. Erickson and R. E. Bennett, Bacteriol. Proc., p. 65, 1961; Erickson and Bennett, Appl. Microbiol. 13:738, 1965. This was observed with a penicillin-nonproducing strain, Wis 49408 (obtained from the University of Wisconsin), and with a penicillinproducing strain, P-5009 (obtained from the Squibb culture collection). It was of interest, therefore, to examine the reversibility of these reactions. For this work, the Wis 49-408 strain, and a penicillin-producing strain, SC 3576, obtained from the Squibb culture collection, were employed. Cultures were grown in the absence of side-chain precursor on synthetic germination and fermentation media as previously described (Erickson and Bennett, Appl. Microbiol. 13:738, 1965). After 48 hr of growth on the fermentation medium, both strains were tested as growing cultures and as suspensions of washed mycelia. The pH of both cultures at 48 hr was near neutrality and was not adjusted. For washed mycelial suspensions, mycelia of a 48-hr culture were collected on a filter in a Buchner funnel by vacuum filtration, washed thoroughly with 0.5% sodium chloride, and then dried for 5 min on the filter while air was drawn through the mycelial pad. Suspensions were prepared by adding mycelia to 0.1 M potassium phosphate buffer of pH 6.8 in the ratio of 1.0 g (wet weight) of mycelium to 7.0 ml of buffer. To each reaction was added 4.8 ml of culture or suspension and the following as indicated: 115 ,umoles of 6-APA and 37.0 ,umoles of the potassium salt of either phenylacetic or phenoxyacetic acid (added from stock solutions of 50 mg/ml adjusted to pH 6.8). Total volume