PURIFICATION AND SOME PROPERTIES OF S‐100 PROTEIN FRACTIONS FROM SHEEP AND PIG BRAINS

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Abstract— The S‐100 protein fraction of pig and sheep brain was purified in 40 per cent yield by a modification of the procedure of Moore (1965), which avoided selective loss of S‐100 components. The S‐100 fraction of both pig and sheep is a mixture of proteins as indicated by acrylamide gel electrophoresis and N‐terminal amino acid analysis. Differences in amino acid composition, electrophoretic heterogenity and N‐terminal analysis were found.One fraction (fraction A) was isolated by DEAE‐Sephadex chromatography from pig brain S‐100 protein fraction. It was considered to be a single protein since it migrated as a single band on acrylamide gel electrophoresis and showed a single symmetrical peak during ultracentrifugal analysis. Only one N‐terminal amino acid was detected in fraction A. The amino acid composition of this fraction showed minor but significant differences from that of the complete S‐100 protein fraction from pig brain. The S‐100 protein fraction of both species, as well as fraction A, had similar s20, w values and similar molecular weights (about 20,000) as indicated by gel filtration. These results, together with the immunological data obtained by other authors, suggest that the proteins of the S‐100 fraction are closely related; the heterogeneity of the S‐100 protein fraction may be of the same type as the lactate dehydrogenase isoenzymes.

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