Ml. Bonet et al., KINETIC MECHANISM OF HALOBACTERIUM-HALOBIUM MN2-ACTIVATED ALKALINE-PHOSPHATASE(), Biochemistry and molecular biology international, 34(6), 1994, pp. 1109-1120
The extreme halophilic archaebacterium Halobacterium halobium contains
an atypical alkaline phosphatase which is selectively activated by Mn
2+ ions (Bonet et al., 1991: Int. J. Biochem. 23, 1445-1451). Enzyme k
inetic mechanism in the presence of Mn2+ with p-nitrophenylphosphate a
s substrate was analysed by initial rate and product and competitive i
nhibition studies. The results indicate that there is an ordered addit
ion of activator and substrate, Mn2+ being first in binding to the pho
sphatase, and that inorganic phosphate is the last product in leaving
the enzyme active site. Strong inhibition by vanadate suggests that a
phosphoenzyme intermediate is formed during enzymatic phosphohydrolysi
s of substrate.