Protein phosphorylation and the regulation of cation cotransport

The turkey erythrocyte is a useful system in which to investigate the relationship between protein phosphorylation and membrane transport. This cell possesses a catecholamine- and cyclic AMP-stimulated Na+-K+ 'cotransport' system in its plasma membrane, and the physiological properties of this system have been partially elucidated. It is distinct from the Na+-K+ 'pump' and is insensitive to ouabain, but can be blocked by certain diuretic agents such as furosemide and bumetanide. A plasma membrane protein of MW 230000, called goblin, has been identified as the major protein whose state of phosphorylation increases upon incubation of turkey erythrocytes with catecholamines or cyclic AMP. The kinetics of phosphorylation of goblin at its cyclic AMP-sensitive sites correlate well with the kinetics of Na+-K+ cotransport activation under various conditions. This protein may play a role in the regulation of the Na+-K+ cotransport system by catecholamines and cyclic AMP.