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American Journal of Clinical Nutrition, Vol 22, 1250-1263, Copyright © 1969 by The American Society for Clinical Nutrition, Inc.

Zinc-Dependent Enzymes in Zinc-Depleted Rats; Intestinal Alkaline Phosphatase

JOHN G. REINHOLD PH.D.1 and GEORGE A. KFOURY PHARM.D.1

1 From the Department of Biochemistry, American University of Beirut, Beirut, Lebanon

The effect of zinc depletion upon the behavior of the intestinal alkaline phosphatases of the rat has been examined by means of electrophoresis on polyacrylamide gels, chromatography on DEAE-cellulose, and kinetic and inhibition studies both of mucosal homogenates and of preparations partly purified by the method of Morton (30).

Electrophoretic separations gave less well resolved phosphatase isoenzyme patterns in the homogenates of depleted rats than in their pair-fed controls. In addition, a slowly migrating isoenzyme was absent or attenuated in electropherograms of the partly purified preparations.

Four isoenzymes were separated by chromatography of the partially purified phosphatase of the control rats. Their counterparts were detected in all eluates of similar preparations from zinc-depleted rats. The distribution of phosphatase activity was studied in three of the isoenzymes. This differed from that in the controls in each of three series of rats, but variability in the latter prevented evaluation of the significance of these differences.

Kinetic studies showed that the action of zinc in increasing reaction velocity was dependent upon pH, the effect being minor at pH 9.5 but marked at pH 10.5. Addition of zinc to the phosphatase measurement systems caused activity to increase to the same extent in zinc-depleted and control rats. Zinc depletion significantly decreased the affinity of phosphatase for zinc and for magnesium, but had no effect upon that for p-nitrophenylphosphate. A marked increase in the affinity of phosphatase for the latter was effected by zinc both in depleted and control rats.

An enhanced susceptibility to inhibition by l-phenylalanine was characteristic of partly purified enzyme preparations from one group of zinc-depleted rats.

It is concluded that zinc depletion in the rat is associated with alterations in enzyme behavior that probably stem from modifications in enzyme structure brought about by zinc depletion. These are not rectified by addition of zinc to enzyme assay systems. It is suggested that they lead to an increase in protein turnover.






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Copyright © 1969 by The American Society for Nutrition