Regulation of alkaline phosphatase and the relation with calcification in hard tissues.

The activity of calf bone alkaline phosphatase(AlP)was regulated with temperature and pH.At the temperature above32-35°C，the substrate saturation curve was a Michaelis type at pH10.5 or a substrate inhibition type at pH7.5。Below32-35°C，on the other hand，the possitive and negative cooperativities were observed at pH10.5and7.5，respectively.The reexamination of AlP activity for phosphoamino acids(P-Tyr，P-Ser and P-Thr)with&lt；^(31)P&gt；NMR spectroscopy indicated：(1)in the one-substrate system，the initial velocity of dephosphorylation was identical among three phosphosphoaminino acids，but veloch with-thate P；(2)in the two-substrate system，both of the initial and post-steady state velocities with P-Tyr were higher than those with P-Ser and P-Thr；and(3)alcoholic hydroxyl group in Ser or Thr as the dephosphorylation product was rephosphorylated by the transphosphorylase action of AlP.These facts implies that the physiological function of the enzyme in vivo may be the regulation of phosphate concentration in hard tissues with the transphosphorylation action。

The activity of calf bone alkaline phosphatase (AlP) was regulated with temperature and pH. At the temperature above 32-35 ゜C, the substrate saturation curve was a Michaelis type at pH 10.5 or a substrate inhibition type at pH 7.5. Below 32-35 ゜C, on the other hand, the possitive and negative cooperativities were observed at pH 10.5 and 7.5, respectively.The reexamination of AlP activity for phosphoamino acids (P-Tyr, P-Ser and P-Thr) with <^(31)P> NMR spectroscopy indicated: (1) in the one-substrate system, the initial velocity of dephosphorylation was identical among three phosphoamino acids, but the velocity with P-Tyr after the steady state was higher than those with P-Ser and P-Thr; (2) in the two-substrate system, both of the initial and post-steady state velocities with P-Tyr were higher than those with P-Ser and P-Thr; and (3) alcoholic hydroxyl group in Ser or Thr as the dephosphorylation product was rephosphorylated by the transphosphorylase action of AlP. These facts implies that the physiological function of the enzyme in vivo may be the regulation of phosphate concentration in hard tissues with the transphosphorylation action.