The Turnover of Myelin Proteins in Adult Rat Brain

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Abstract
The turnover of proteins of myelin of brain was followed after an intracerebral injection of [1-14C] leucine into adult rats and compared with the turnover of proteins of total brain homogenate, microsomal and supernatant fractions. The myelin proteins were separated into three major fractions, viz., the Wolfgram, proteolipid and basic proteins as fluorescamine derivatives by a new preparative sodium-dodecylsulfate-polyacrylamide slab gel electrophoresis method. The bands were visualized, without staining, by their fluoresence under UV light. The maximal incorporation was in the microsomal proteins followed by supernatant proteins. The maximum amount of incorporation into myelin proteins was about 11 % of that in the microsomal proteins. The incorporation of the label in myelin proteins reached a maximum about six hr after the injection, while the microsomal and supernatant proteins had already reached a maximum at 30 min. The specific radioactivity of the microsomal, supernatant and myelin proteins declined at multiphasic rates with half-lives varying from three hours to several days. Individual myelin proteins also appeared to turn over at multiphasic rates, with half-lives of 5, 20 and 90–100 days for the Wolfgram proteins, 7 and 100–120 days for the proteolipid proteins and 5 and 80–110 days for the basic proteins.