Glycogen phosphorylase and its converter enzymes in haemolysates of normal human subjects and of patients with type VI glycogen-storage disease. A study of phosphorylase kinase deficiency

Abstract

1. The properties of phosphorylase a, phosphorylase b, phosphorylase kinase and phosphorylase phosphatase present in a human haemolysate were investigated. The two forms of phosphorylase have the same affinity for glucose 1-phosphate but greatly differ in Vmax. Phosphorylase b is only partially stimulated by AMP, since, in the presence of the nucleotide, it is about tenfold less active than phosphorylase a. In a fresh human haemolysate phosphorylase is mostly in the b form; it is converted into phosphorylase a by incubation at 20degreesC, and this reaction is stimulated by glycogen and cyclic AMP. Once activated, the enzyme can be inactivated after filtration of the haemolysate on Sephadex G-25. This inactivation is stimulated by caffeine and glucose and inhibited by AMP and fluoride. The phosphorylase kinase present in the haemolysate can also be measured by the rate of activation of added muscle phosphorylase b, on addition of ATP and Mg2+. 2. The activity of phosphorylase kinase was measured in haemolysates obtained from a series of patients who had been classified as suffering from type VI glycogenosis. In nine patients, all boys, an almost complete deficiency of phosphorylase kinase was observed in the haemolysate and, when it could be assayed, in the liver. A residual activity, about 20% of normal, was found in the leucocyte fraction, whereas the enzyme activity was normal in the muscle. These patients suffer from the sex-linked phosphorylase kinase deficiency previously described by others. Two pairs of siblings, each time brother and sister, displayed a partial deficiency of phosphorylase kinase in the haemolysate and leucocytes and an almost complete deficiency in the liver. This is considered as being the autosomal form of phosphorylase kinase deficiency. Other patients were characterized by a low activity of total (a+b) phosphorylase and a normal or high activity of phosphorylase kinase in their haemolysate.