In vitro effect of ascorbic acid on bovine kidney alkaline phosphatase activity

A striking decrease of bovine kidney alkaline phosphatase activity is observed in vitro when the catalytic assay is performed after preincubation of the enzyme with ascorbic acid (AA). The inhibitory effect is a function of AA concentration time and on temperature. Activity decay follows an exponential biphasic course as a function of preincubation time composed by a "fast" phase in the first half hour and by a later "slow" phase of inhibition. Both the rise in preincubation temperature and the increase of the amount of vitamin enhance the degree of inhibition. Ascorbic acid is ineffective as inhibitor when added together with the substrate, p-nitrophenyl phosphate, which in fact markedly stabilizes the enzyme even when present in unsaturating amounts.