Studies on the N-acetyl-beta-D-hexosaminidase B from germinating Lupinus luteus L. seeds. II. Mechanism and inhibition with some 2-acetamido-2-deoxyaldono(1----4)lactones.
The N-acetyl-beta-D-hexosaminidase B of germinating yellow lupin seeds catalyzed the hydrolysis of both p-nitrophenyl-N-acetyl-beta-D-glucosaminide and -galactosaminide substrates. The investigation of the pH dependence of the kinetic parameters (Vmax and Vmax/Km) 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----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.
Pócsi
I
I
Institute of Biochemistry, Lajos Kossuth University, Debrecen, Hungary.
Kiss
L
L
Zsoldos-Mády
V
V
Pintér
I
I
D000606:Amino Sugars / Q000494:pharmacology*; D001665:Binding Sites; D002384:Catalysis; D006595:Hexosamines / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D007783:Lactones / Q000494:pharmacology*; D012639:Seeds / Q000201:enzymology*; D001619:beta-N-Acetylhexosaminidases / Q000037:antagonists & inhibitors / Q000378:metabolism*
D000606:Amino Sugars; D006595:Hexosamines; D007783:Lactones; D001619:beta-N-Acetylhexosaminidases