On the component proteins of calf thymus nucleoprotein

By a study of experimental variables, a standardized procedure for the preparation of calf thymus nucleoprotein of essentially constant phosphorus and sulfur content has been developed. The nucleic acid-free protein has been isolated quantitatively by a modified Sevag-Mirsky procedure. The protein has been quantitatively separated into histone and residual protein by treatment with HCl at pH 2.5. The histone precipitated as a single substance, but on ultracentrifugation showed two components. These have been separated and partly characterized. One (“fast”), representing 63% of the histone and yielding molecular weight estimates of 130,000–140,000, contains 0.23% tryptophan, 0.67% cystine, and 2.4% methionine. The other component (37%, “slow”), of estimated molecular weight of 11,000–16,000, contains0.82% methionine, and is free of tryptophan and cystine.