title: Kinetic mechanism of Halobacterium halobium Mn(2+)-activated alkaline phosphatase.
abstract: The extreme halophilic archaebacterium Halobacterium halobium contains an atypical alkaline phosphatase which is selectively activated by Mn2+ ions (Bonet et al., 1991: Int. J. Biochem. 23, 1445-1451). Enzyme kinetic mechanism in the presence of Mn2+ with p-nitrophenylphosphate as substrate was analysed by initial rate and product and competitive inhibition studies. The results indicate that there is an ordered addition of activator and substrate, Mn2+ being first in binding to the phosphatase, 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 phosphohydrolysis of substrate.
authors.affiliation: División de Bioquímica, Facultad de Ciencias, Universidad de Alicante, Spain.
authors.forename: M L
authors.initials: ML
authors.lastname: Bonet
authors.forename: F I
authors.initials: FI
authors.lastname: Llorca
authors.forename: E
authors.initials: E
authors.lastname: Cadenas
mesh_terms: D000469:Alkaline Phosphatase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D001149:Arsenates / Q000494:pharmacology; D001665:Binding Sites; D003300:Copper / Q000494:pharmacology; D004789:Enzyme Activation; D004791:Enzyme Inhibitors; D019617:Halobacterium salinarum / Q000201:enzymology*; D007700:Kinetics; D008345:Manganese / Q000378:metabolism / Q000494:pharmacology*; D009532:Nickel / Q000494:pharmacology; D009596:Nitrophenols / Q000378:metabolism; D009943:Organophosphorus Compounds / Q000378:metabolism; D010710:Phosphates / Q000494:pharmacology; D010766:Phosphorylation; D014638:Vanadates / Q000494:pharmacology
chemical_list: D001149:Arsenates; D004791:Enzyme Inhibitors; D009596:Nitrophenols; D009943:Organophosphorus Compounds; D010710:Phosphates; C008644:nitrophenylphosphate; D014638:Vanadates; D008345:Manganese; D003300:Copper; D009532:Nickel; D000469:Alkaline Phosphatase; C025657:arsenic acid