5′‐Nucleotidase in Rat Brain Myelin

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Abstract
Rat brain myelin showed substantial activity of 5''-nucleotidase. The specific activity in myelin was enriched 2- to 3-fold over that in rat brain homogenates, and the total activity in myelin accounted for approximately 24% of the activity in the homogenates. The 5''-nucleotidase in the homogenates and in isolated myelin had optimum activity at pH 7.5-9.0, was stimulated by Mg2+ and Mn2+ and was inhibited by Co2+, Zn2+, EDTA and EGTA [ethyleneglycol bis-(.beta.-aminoethyl ether)-N-N''-tetraacetic acid]. 5''-AMP, 5''-UMP and 5''-CMP were the preferred substrates; 5''-GMP was hydrolyzed at approximately 1/2 the rate of the other mononucleotides. The very low rates of cleavage of .beta.-glycerophosphate and 2''-AMP ruled out any significant contribution of nonspecific phosphatase to the observed 5''-nucleotidase activity in myelin. The 5''-nucleotidase was inhibited by concanavalin A and was protected by .alpha.-methyl-D-mannoside against inhibition by concanavalin A, suggesting that this enzyme in the CNS is a glycoprotein. The myelin sheath may be 1 major locus of 5''-nucleotidase in the rat brain. 5''-Nucleotidase is regarded as functioning in the facilitation of adenosine transport across membranes, and its activity in the myelin sheath suggests that myelin may play a role in biological transport.