J. Biol. Chem., Vol. 261, Issue 24, 10996-11002, 08, 1986
Mechanism of activation by anions of phosphoglycolate phosphatases from spinach and human red blood cells
ZB Rose, DS Grove and SN Seal
Phosphoglycolate phosphatases from spinach and human red blood cells show a
number of common features not often found in enzymes. Both enzymes are
activated more than 50-fold by millimolar concentrations of Cl-. Other
inorganic anions and a number of carboxylic acids also activate. Each
enzyme has limited substrate specificity yet each hydrolyzes P-glycolate
and ethyl-P with the same maximal velocity. L-P- lactate is only a good
substrate for the red cell enzyme. With both enzymes initial rate data
obtained by varying both the P-glycolate and Cl- give parallel line double
reciprocal plots. Similar experiments with ethyl-P as substrate give
intersecting lines with both enzymes. The likelihood that both classes of
substrates are acting at the same site is strengthened by the results of
inhibition studies with alternative substrates and the constancy of
inhibition constants for glycolate with all substrates for a given enzyme.
For each substrate the experimentally observed variation in V/Km with
different activators is small, suggesting that the enzyme has an ordered
mechanism with the phosphorylated substrate reacting first. A mechanism
that is consistent with all of the data is presented.