Possible mechanism of inhibition of cartilage alkaline phosphatase by insulin.

The inhibition of alkaline phosphatase by insulin is a finding reported by many researchers but the mechanism of this inhibition has not been studied. Since alkaline phosphatase is an important factor in the mechanism of calcification and an impairment of mineralisation has been observed in diabetes mellitus, a study was carried out to assess the effect of the hormone on alkaline phosphatase measured in chondrocytes, in matrix vesicles and in a purified enzyme preparation. Enzyme activity was inhibited by insulin. The lowest active concentration was 10(-6) M and maximal inhibition was obtained at about 10(-4) M. The inhibition is of the uncompetitive type. Full recovery of the hormone-inhibited enzyme was obtained with 10(-4) M 2-mercaptoethanol. Data suggest direct interaction between the alkaline phosphatase and insulin molecules, involving either disulfide cross linkages or the metal chelating activity of insulin.