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Cyclic Nucleotide-Dependent Protein Kinase Modulators in Thyroid Tissue^*

Thyroid Study Unit, Department of Medicine, University of Chicago Chicago, Illinois 60637

Address requests for reprints to: Dr. Leslie J. DeGroot, Section on Endocrinology, Department of Medicine, University of Chicago, 950 East 59th Street, Chicago, Illinois 60637.

Abstract

A heat-stable protein which inhibits cAMP dependent protein kinase was prepared from the bovine thyroid 100,000 x g supernatant. This protein inhibited the cAMPdependent protein kinase both from bovine thyroid cytosol and bovine thyroid plasma membranes. The inhibitory effect was noncompetitive with histone as substrate of the cytosolic enzyme.

The stimulatory modulator for cGMP-dependent protein kinase was separated from the 100,000 x g supernatant by Sephadex G-100 gel filtration. The stimulatory modulator had no stimulating effect on cAMP-dependent phosphorylation, and the inhibitory modulator of cAMP-dependent enzyme had no effect on cGMP-requiring phosphorylations.

The inhibitory modulator may regulate cAMP-dependent protein kinase activity in cytosol and plasma membrane, and the stimulatory modulator for cGMP-dependent protein kinase may have a role in thyroid function independent of the cAMP-requiring system. (Endocrinology 105: 204, 1979)

Footnotes

^* This work was supported by USPHS Grants AM-13377 and CA- 19266.

Received August 25, 1978.