Studies on the B from germinating Lupinus luteus L. seeds II. Mechanism and inhibition with some 2-acetamido-2-deoxyaldono(1 å 4)lactones

The N- acetyl -β- d - hexosaminidase B of germinating yellow lupin seeds catalyzed the hydrolysis of both N- acetyl -β- d - glucosaminide and -galactosaminide substrates. The investigation of the pH dependence of the kinetic parameters ( V max and V max / K m ) demonstrated that two common ionizable groups (probably two carboxyl groups) play an essential role in the catalysis. That is, the enzyme has a lysozyme-like splitting mechanism, and the possibility of an anchimeric assistance provided by the acetamido group seems to be negligible. The presence of a deprotonated carboxyl group near the glycosidic linkage was also supported by inhibition with 1-thio substrate analogues. On the other hand, some 2-acetamido-2-deoxyaldono(1 a 4)lactones proved to be effective inhibitors of the hexosaminidase with the exception of the d -arabinose derivative, which can be explained by high stereospecificity in the binding.