Chicken liver H-protein, a component of the glycine cleavage system. Amino acid sequence and identification of the N epsilon-lipoyllysine residue.

The complete amino acid sequence of H-protein from chicken liver was determined by aligning peptides obtained by cyanogen bromide, endoproteinase Lys-C, Staphylococcus aureus V8 protease, and chymotrypsin cleavage together with the partial NH2- and COOH-terminal sequence of the intact protein. H-protein consists of 125 amino acids and a lipoic acid moiety linked to lysine 59. The sequence is: (sequence in text). The lysyl residue involved in lipoic acid attachment is indicated with an asterisk. The molecular weight including lipoic acid is calculated to be 13,883. From the secondary structure predicted by the method of Chou and Fasman (Chou, P. Y., and Fasman, G. D. (1978) Adv. Enzymol. 47, 45-148) the lipoic acid binding region shows alpha-helical structure and is predicted to be an interior portion of the protein from the hydropathic profile according to Kyte and Doolittle (Kyte, J., and Doolittle, R. F. (1982) J. Mol. Biol. 157, 105-132).