Inactivation of Glycogen Phosphorylase of Human Polymorphonuclear Leukocytes

Abstract

Glycogen phosphorylase of human polymorphonuclear leukocytes is dephosphorylated during incubation of a gel-filtered cell extract. The dephosphorylated enzyme (b form) retains 25 per cent of the activity of the phosphoenzyme (a form) when measured without AMP but at high glucose-1-phosphate concentrations. The ratio of activity -AMP/+AMP for the a enzyme is 0.8–1.0 and for the b enzyme 0.2. Leukocyte phosphorylase is not activated by -SH groups, but the b enzyme is stimulated by 0.4 mol/1 Na₂ sO₄. The phosphatase which catalyzes the conversion of phosphorylase a to b is inhibited by glucose-1-phosphate and AMP both at 14°C and 25°C. Glucose counteracts the AMP inhibition but not the glucose-1-phos-phate inhibition at both temperatures. Glucose alone had no effect at 25°C, but it accelerated the phosphatase reaction at 14°C. Glucoses-phosphate or glycogen alone or in the presence of AMP or glucose-1-phos-phate did not affect the phosphatase reaction. From previous and present experiments it is concluded that the phosphorylase of human polymorphonuclear leukocytes is closely related to liver phosphorylase and that the inactivation of the enzyme is mainly controlled by AMP and glucose.

Key Words:

• Enzyme regulation
• human polymorphonuclear leukocytes
• phosphorylase
• phosphorylase phosphatase