Fractionation of proteins of the microsomes of rat liver by means of a non-ionic detergent.

reasonable to suppose that the ratio k(Gly. Gly)/ kl(Leu. Gly) gives an approximate estimate of the relative selectivities of the reagents towards the splitting of peptide bonds. A simple calculation from the results in Table 2 gives a value of the ratio of 5 for aqueous hydrochloric acid and average values of 16 for methylhydrazine and 22 for hydrazine. Therefore the selectivity of the reagents towards peptide bonds is in the order aqueous acid < methylhydrazine < hydrazine. The lower reactivity of methylhydrazine as compared with hydrazine towards peptide bonds precludes its use as a reagent for the determination of the C-terminal amino acids of proteins, as shown by the failure of the two experiments with insulin. However, it may be useful as a solvent for proteins, since it appears to combine the good solvent properties of hydrazine (as shown by the solubility tests with four proteins) with decreased reactivity towards peptide bonds. For physical measurements on proteins it may be possible to use methylhydrazine in place of hydrazine in order to avoid the degradation which accompanies the use of the latter (Rees & Singer, 1956; Bradbury, 1958a).