Cyclic AMP-binding proteins in chick liver

Abstract

1. 1. Cyclic AMP-binding proteins were found in all subfractions of chicken liver cells. However most of them (about 90% of total cyclic AMP-binding proteins) are present in the cytosol. 2. 2. The lowest cyclic AMP-binding activity in all subfractions of liver cells was determined in 7-day old chicks. Since changes in protein kinase activities in liver cells during chick development do not correspond the changes in cyclic AMP-binding protein activities it seems that subfractions of chick liver cells contain large quantities of cyclic AMP-independent protein kinases as suggested previously by Kaniuga et al. (1975). 3. 3. Cyclic AMP-binding proteins of the nucleus are mostly localized in the soluble protein fraction. They are similar to the cytosolic cyclic AMP-binding proteins with respect to the electrophoretic mobility and the molecular weights. 4. 4. After chromatography of soluble, cytosolic proteins on the Sephadex G-100 column, 5 fractions with molecular weights: over 100,000, about 78,000, 43,000, 26,000 and 14,000 respectively were obtained. All these fractions showed cyclic AMP-binding activities. 5. 5. When chromatography was performed after incubation of the soluble cytosolic proteins with cyclic AMP in order to dissociate the holoenzyme of cyclic AMP-dependent protein kinase only two fractions of cyclic AMP-binding proteins were obtained. Molecular weights of these fractions were: 26,000 and 14,000. 6. 6. An existence of cyclic AMP-binding proteins with similar molecular weights in both nuclear and cytosolic fractions of chick liver seems to suggest that cyclic-AMP binding proteins of cytosolic origin may be translocated to nucleus.