Phosphorylation and dephosphorylation of spectrin from human erythrocyte ghosts under physiological conditions: autocatalysis rather than reaction with separate kinase and phosphatase.

Publisher Website
Google Scholar
Abstract
The mechanism of phosphorylation and dephosphorylation of spectrin from human erythrocyte membranes was examined under closely physiological conditions. Spectrin is apparently an autophosphorylating and dephosphorylating system. Extraction from ghosts of up to 85% of the kinase (casein kinase) suggested to catalyze the reaction only slightly reduced spectrin component 2 phosphorylation and did not affect ATP-induced changes in the ghosts'' shapes. A spectrin-actin complex isolated from endocytotic inside-out vesicles under hypertonic conditions contained virtually no casein kinase activity and still exhibited a largely intact phosphorylation machinery. Photoaffinity labeling experiments indicated that spectrin component 2 fulfills the necessary prerequisite of the hypothesis, i.e., it contains its own ATP-binding site. Under various conditions, spectrin phosphorylation and dephosphorylation seem to be tightly coupled. Implications for the understanding of spectrin function and the maintenance of erythrocyte shape are discussed.