Studies on the aminopeptidase activities of Porphyromonas gingivalis

Porphyromonas gingivalis is an asaccharolytic bacterium that requires nitro gen substrates as carbon and energy sources. The aims of this study were to investigate the aminopeptidase activities of P. gingivalis and to evaluate the effect of aminopeptidase inhibitors on bacterial growth. Only arginine aminopeptidase and dipeptidyl aminopeptidase IV activities were detected. Experimental evidence was obtained suggesting that the Arg-gingipains of P. gingivalis can function as both an endopeptidase and an aminopeptidase. Fi rstly, the arginine aminopeptidase activity was found to be inhibited by le upeptin, a well-known inhibitor of Arg-gingipain activity. Secondly, a prep aration of Arg-gingipain activity could hydrolyze the chromogenic substrate for arginine aminopeptidase. Lastly, a mutant of P. gingivalis constructed via gene disruption by use of suicide plasmids and deficient in both Arg-g ingipain A and B was also devoid of arginine aminopeptidase activity. To in vestigate the key role of aminopeptidase activities in growth of P. gingiva lis, aminopeptidase inhibitors were incorporated in the culture medium prio r to inoculation. Bestatin and actinonin were the only ones to inhibit grow th of P. gingivalis. Their mechanism of growth inhibition appears to be dif ferent but does not involve inhibition of the two major aminopeptidase acti vities (arginine aminopeptidase and dipeptidyl aminopeptidase IV).