Crystalline Leghemoglobin. III. Amino Acid Composition of the Two Main Components.

Abstract

The amino acid composition of the two main components of leghemoglobin has been determined by the chromatographic technique of Stein and Moore. Separate determinations have been made for tryptophan and amide ammonia. The electrophoretically faster component is shown to contain the following amino acid residues Asp12, Thr7, Ser11, Glu14, Pro5, Gly8, Ala21, Val13, Ileu6, Leu12 Tyr3, Phe8, Lys13, His2, Arg1, Try3, ([long dash]CONH2) 8 and the electrophoretically slower component: Asp11, Thr6, Ser10, Glu12, Pro5, Gly6, Ala24, Val14, Ileu4, Leu12, Tyr3, Phe7, Lys13, His2, Arg2, Try3, ([long dash]CONH2)6. Small but significant differences in the amino acid content of the two components involve: Ala, Arg, Glu, Gly, Ileu, and Val. No significant differences are found in the other amino acids of the two main components. The molecular weight of the faster component calculated on the basis of the amino acid content is 16 695 and for the slower one 15 429. The electrophoretic behavior of the two components can be satisfactorily explained on the basis of the amino acid composition. Leghemoglobin differs from other hemin proteins in showing a very low histidine content and the absence of methionine and cysteine. The results are discussed.