Guanosine 3':5'-cyclic monophosphate binding proteins in rat tissues

Abstract

Rat tissues were surveyed for proteins which bind cGMP. Binding activity was high in extracts of lung, cerebellum, and small intestine, but was low in those of liver, adipose tissue, and skeletal muscle. DEAE-cellulose chromatography resolved two peaks of cGMP-binding activity in most tissues. The binding protein in peak 1 was eluted in the flow-through volume and was most abundant in extracts of intestine. It had a sedimentation coefficient of 6S and was highly specific for cGMP at pH 7.0 (dissociation constant KD=0.05 muM). No cGMP-dependent histone kinase activity was found for this peak. The binding protein in peak 2 was eluted by 0.05-0.15 M NaCl and was the predominant binding substance in lung, cerebellum, and heart. It had a sedimentation coefficient of 8S and binding was also highly specific for cGMP, with a KD of 0.05 muM. This peak of binding activity was associated with cGMP-dependent protein kinase activity which could be purified approximately 200-fold by Sepharose 6B chromatography. Cyclic GMP dependency of kinase activity was observed only at low histone concentrations. The abundance of one or both the above binding proteins correlated with the known basal levels of cGMP in the tissues.