In Vitro and In Vivo Binding of S‐Adenosyl‐L‐Homocysteine to Membranes from Rat Cerebral Cortex

Abstract

Membranes from rat cerebral cortex bound S-adenosyl-L-homocysteine (SAH) with a Kd of 5 .cntdot. 10-7 M and n of 170 pmol/g fresh tissue (i.e., 20 mg protein). The binding was enhanced by Mg2+ and Ca2+ but not K+ and Na+. .gamma.-Aminobutyric acid, diazepine, noradrenaline [norepinephrine] and .alpha. antagonists had no effect; S-adenosyl-L-methionine, adenosine and ATP inhibited SAH binding. Linkage with an adenosine receptor was not demonstrated. SAH binding proteins were more abundant in the crude synaptosomal pellet (P2). A similar fixation seemed to occur on brain membranes after [3H]SAH administration to rat. The binding might be linked to a methylase activity or an adenosine receptor.