Comparisons between the alpha chain of bovine thyrotropin and the CI chain of luteinizing hormone. Compositions of tryptic peptides, cyanogen bromide fragments, and carbohydrate moieties.

The tryptic peptides of reduced, S-carboxymethyl CI chain of bovine luteinizing hormone have been isolated by gel filtration and electrophoresis or chromatography on paper. The amino acid compositions of all peptides are identical with those of the OL chain of thyroid-stimulating hormone (TSH), whose sequence is described in the preceding communication. Chymotryptic-like cleavages also yielded the same peptides. Large fragments of CI chain, obtained either by cleavage with cyanogen bromide or tryptic hydrolysis of the maleylated, reduced, S-carboxymethyl derivative, were also separated, primarily by gel filtration. Although all these fractions were not completely purified, their compositions agreed well with the corresponding TSH-a! fragments and the data demonstrate that the order of the tryptic peptides must be the same in both chains. Some heterogeneity was observed in various preparations of CI chain. A portion of one preparation appeared to lack the amino-terminal dipeptide, Phe-Pro, as does some TSH-a. The composition of another preparation indicated it to contain 1 less residue of phenylalanine than that studied in detail. While complete sequences of the tryptic peptides remain to be determined, the data show that the CI chain and TSH-oc must have identical amino acid sequences other than minor heterogeneity or possible inversions or substitutions within the tryptic peptides. The two chains do, however, differ in their carbohydrate composition with a larger amount of mannose in the CI chain of luteinizing hormone most apparent.