A study of the proteinase content and the chromatography of thymus histones

Abstract

Calf-thymus histones prepared by acid extraction of sodium chloride-washed deoxynucleoprotein contained a proteinase (partly inhibited by mM diisopropyl phosphorofluoridate), which gave rise to extra N-terminal alanine, lysine and glycine residues in the histones, especially at pH 7-8. Histones prepared under conditions minimizing this proteolysis had proline and alanine N-terminal groups accounting for up to 96% of all end groups and amounting to 1 mole/30, 000-40, 000 weight of histone. These 2 end groups pre-existed in the deoxynucleohistone and were not produced by the acid extraction. On carboxymethylcellulose columns run with dilute HC1 as eluent. the histones gave 2 main peaks, accounting for at least 86% of the histones. The 1st peak had mainly proline, the 2nd mainly alanine N-terminal groups. The 2 column fractions have been compared in yield, end groups and amino acid composition with the 2 fractions resulting from the sodium chloride-ammonia fractionation of the histones.