Effect of Parathormone on Bone Phosphatase Activity in vitro

The relationship between hormonal and enzymic activity is of considerable biological interest. Kay 1 noted high plasma phosphatase values in generalized ostitis fibrosa. Page 2 reported a decrease in the bone phosphatase in rats after parathormone injections. Bodansky and Jaffe 3 obtained increases in plasma phosphatase 8 hours after injection of single large doses in the dog and decreases in the guinea-pig after 1 and 2 days.

Heymann 4 reported a direct effect of parathormone in vitro. He observed decreases of 50 to 100% in bone phosphatase activity when 0.1 units of parathormone were added per cc. of hydrolysing mixture. The effect on kidney and intestinal phosphatase was much less marked. He conducted his experiments at a pH of 7.7 using a 50% concentration of a phosphatase preparation which had been extracted from the tissue with glycine buffer. Sodium glycerophosphate and hexosephosphate were employed as substrates. The parathormone was added in a glycine solution.

We have studied the effect of parathormone∗ on the phosphatase activity of aqueous extracts of rat and cattle bone. The sodium diethylbarbiturate buffer of Michaelis was used. This buffer in 0.5% concentration is without effect on phosphatase activity and hence is to be preferred to glycine which, in the concentrations used . for buffering, retards phosphatase activity about 30%. 5 The technique of tissue phosphatase activity estimation was similar to that used in previous studies. 5 0.0127 M sodium β glycerophosphate (Eastman Kodak) was used as the substrate. The reciprocal of the time in minutes necessary to liberate 0.05 mg. of inorganic phosphate as P per cc. of hydrolyzing mixture was used as the measure of enzyme activity (Q).