| Abstract: | Isotopic exchange of (35)S between penicillins and 6-amino-penicillanic acid (6-APA) was observed in cell-free extracts of Penicillium chrysogenum. Sulfhydryl-containing compounds were required for activity. Dithiothreitol, dithioerythritol, mercaptoethanol, and glutathione served as activators. The acyltransferase was purified threefold by adsorption on calcium phosphate gel at pH 6 and elution at pH 8. The partially purified enzyme showed maximal activity at pH 8. The enzyme was stable at 25 C for at least 30 min at pH 8. Dissociable inhibitors or activators, other than the sulfhydryl-containing compounds, could not be demonstrated in the enzyme preparation. An apparent Michaelis constant of 1.5 +/- 0.5 mm was determined for penicillin G at a 6-APA concentration of 5 mm. The enzyme did not appear to possess penicillin amidase activity. The exchange mechanism probably involves an acyl-enzyme intermediate. Penicillins V, G, K, X, and dihydro F showed isotopic exchange with (35)S-6-APA. Penicillin N, methylpenicillin, and phenyl-penicillin did not show exchange. The level of acyltransferase in P. chrysogenum 51-20F3 was measured at times during the fermentation. The level of activity increased threefold between 40 and 55 hr, remaining high until about 90 hr. |
