Occurrence of an ascamycin dealanylating enzyme, Xc-aminopeptidase, in mammalian cell membranes and susceptibility to ascamycin.

An ascamycin dealanylating enzyme (Xc-aminopeptidase) has been isolated from Xanthomonas citri and characterized as a proline iminopeptidase of molecular weight of 38,000 (H. OSADA & K. ISONO, Biochem. J. 233: 459 approximately 463, 1986). Immunological studies have shown that all the mammalian cells tested possess a closely-related enzyme(s) on their cell membranes. This enzyme is more active in transformed cells than in nontransformed cells. A decreased ratio of ID50 (ascamycin/dealanylascamycin based on [35S]methionine uptake) in transformed cells compared with the nontransformed cell can be explained on the basis of the conversion of ascamycin to dealanylascamycin by the enzyme. It is suggested that ascamycin cannot be transported through mammalian cell membranes but dealanylascamycin can permeate; a similar situation exists in prokaryotic cells.