Protein phosphorylation and sodium conductance in nerve membrane.

Abstract

High MW proteins extracted from the walking nerves of the shore crab (Carcinus maenas) exhibit a cycle of phosphorylation-dephosphorylation that is influenced by neurotropic compounds and inorganic ions. The net phosphorylation state of the proteins is increased in the presence of K+ ions and decreased with Na+ ions. In the absence of Mg2+, there is no phosphorylation. Ca2+ ions at low concentrations are necessary for optimal phosphorylation. At high concentration (> 0.1 mM), Ca2+ ions are inhibitory. Neurotropic compounds generally inhibit the phosphorylation process. More specifically, tetrodotoxin and veratridine, depending on the ionic composition of the medium, have opposite effects on the phosphorylation process, a result in agreement with their known physiological action. The high MW components are part of the Na permeation sites and the conductance state of those sites is controlled by a phosphorylation process.