SLOW STEP IN ACTIVATION OF MUSCLE GLYCOGEN-PHOSPHORYLASE-B BY ADENOSINE 5'-MONOPHOSPHATE

The incubation of glycogen phosphorylase b from rabbit skeletal muscle s with the allosteric activator (AMP) for 10-15 min has been found to result in an additional increase in the initial rate of the enzymatic reaction (v) as compared with the corresponding value of v measured by the initiation of the enzymatic reaction by the addition of a mixture of glucose I-phosphate and AMP (0.02 M HEPES, pH 6.8; 37 degrees C). Glycogen with molecular mass of 270 . 10(6) daltons was used in the ki netic experiments. It is assumed that the enhancement of the rate of t he phosphorylase b reaction is due to association of the enzyme molecu les adsorbed to a glycogen particle resulting in an increase in the af finity of the enzyme for glycogen.