Abstract
Properties of cyclic AMP-dependent protein kinases from skeletal, heart and diaphragm muscles of hypothyroid rats were compared. Increased enzyme activity was observed in skeletal muscle from hypothyroid rats after DEAE-cellulose chromatography. Changes in isozyme distribution were also shown in the hypothyroid status. The elution profile on DEAE-cellulose suggested a possible translocation of the enzyme from the particulate to the soluble fraction in the heart of hypothyroid rats. The turnover rate of the enzyme protein decreased in the skeletal muscle of hypothyroid rats, but the other two organs showed no change even in the hypothyroid status. The activity of heat-stable protein kinase inhibitor increased in the skeletal and the diaphragm muscles in hypothyroid rats, whereas the activity in the heart decreased in the hypothyroid status. These data suggested the possibility that changes in enzyme properties, modification of isozyme distribution, and changes in modulator activity might account for the modulation of muscle function in hypothyroid rats.
