Metal Complexes of Phosphoglucomutase in Vivo

• Published in: The Journal of biological chemistry 1971-02, Vol.246 (4), p.1160-1167
• Main Authors: Peck, Ernest J., Ray, William J.
• Format: Article
• Language: English
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1016/S0021-9258(18)62444-5

A procedure is presented for measuring the relative amounts of the Mg 2+ and Zn 2+ forms of phosphoglucomutase in rabbit muscle extracts. The results indicate that the ratio of these forms in vivo is the same as that observed in extracts in vitro , viz ., about 0.5 for mature Purdue Dutch rabbits; other phosphoglucomutase·metal species do not appear to be present in appreciable amounts. The concentration of free Mg 2+ in such extracts is saturating with respect to phosphoglucomutase. These observations, together with metal binding data, provide estimates of the relative concentrations of free Mg 2+ and free Zn 2+ in vivo , about 10 6 to 1, and of the actual concentration of free Zn 2+ , about 10 -10 m . The fraction of the total endogenous phosphoglucomutase in the Mg 2+ form was essentially constant in animals treated alike; however, this fraction varied markedly in animals subjected to different treatments; viz ., the fraction depended on the physiological state of the animal. Thus the fraction of the total enzyme in the Mg 2+ form could be increased from about 0.35 ± 0.10 to about 0.83 ± 0.08 (S.D.) by treatment with insulin in fasting animals. By contrast, the total enzyme per ml of standard extract varied among animals by less than 8% (S.D.), regardless of treatment. Since the Zn 2+ form of phosphoglucomutase is essentially inactive, these results indicate that the average catalytic efficiency of phosphoglucomutase can vary with the physiological state of the animals, while the total catalytic potential remains unchanged.