Reaction of alpha-mannosidase from Phaseolus vulgaris with group-specific reagents. Essential carboxyl groups.
When the pKm of alpha-mannosidase was determined at different pH values, the results indicated that ionizable groups with pK values of approx. 3.8 and 5.7 could be essential. Modification with carbodiimide or Woodward's Reagent K abolished the enzyme activity. The substrate analogue, alpha-methyl-D-mannoside, protected the enzyme against inactivation. Incorporation of a 14C-labeled nucleophile reagent in the presence or absence of the analogue suggested that 2--4 carboxyl groups were protected. Exchange studies indicated that the essential Zn2+ could be bound to such groups. There was no indication that hydroxyl groups, sulphydryl groups, guanidino groups or amino groups take part in the catalytic activity.
D001665:Binding Sites; D002234:Carbodiimides / Q000494:pharmacology; D002264:Carboxylic Acids; D055598:Chemical Phenomena; D002621:Chemistry; D007887:Fabaceae / Q000201:enzymology*; D006639:Histidine; D006863:Hydrogen-Ion Concentration; D008361:Mannosidases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D010946:Plants, Medicinal; D015032:Zinc / Q000378:metabolism
D002234:Carbodiimides; D002264:Carboxylic Acids; D006639:Histidine; D008361:Mannosidases; D015032:Zinc