ABSTRACT
The diverse metal requirements for activity of the phosphoprotein phosphatases (EC 3.1.3.16) concerned with glycogen metabolism in rat liver were postulated to reflect the diverse binding intensities of their essential metal(s). After inactivation by fluoride, three of these phosphatases had similar metal requirements in contrast to a fourth phosphatase. Further similarities led to a grouping of these enzymes into two general types. Phosphatases designated type 1 consisted of three enzymes which had the following properties; (1) preference for glycogen phosphorylase a as a substrate; (2) molecular weights in excess of 100 000; (3) conversion to an active 30 000 dalton 'subunit' form upon selective denaturation by 80% ethanol; (4) diverse degrees of stimulation by metals (Mg2+ and Mn2+); and (5) changes to an absolute dependence upon added Mn2+ (but not Mg2+) for activity of both the holoenzyme and the subunit after a demetallating treatment with fluoride in EDTA. The phosphatase designated type 2 exhibited the following properties; (1) preference for glycogen synthase D as a substrate; (2) molecular weight of 50 000; (3) no conversion to an active 30 000 dalton subunit form upon selective denaturation by 80% ethanol; (4) complete metal-dependence upon either Mg2+ or Mn2+; and (5) no change to an absolute dependence on added Mn2+ for activity after a demetallating treatment with fluoride in EDTA.
