The assimilation of amino acids by bacteria. 25. The preparation and activities of a factor involved in the incorporation of amino acids in disrupted staphylococcal cells

AMINO ACID COMPOSITION OF CYTOCHROME c 611 amide groups in the molecule there is an excess of some 12 basic groups over acidic groups, and this is in keeping with the basic properties of cyto- chrome c. The values quoted for the sulphur-containing amino acids in Table Our experience suggests that the methods used in the present work are not suitable for accurate determination of these amino acids, but in the absence of other values we have put forward those that appear most likely, that is, two methionine and two cysteine residues/molecule of cytochrome c. It is not known whether the conditions of hydrolysis used here were sufficiently vigorous to split the thioether bonds linking the prosthetic group to cysteine residues in the protein. If so, these may be the only cysteine residues in the protein. Akeson (1942) and Pal6us (1955) concluded that this was true of cytochrome c from cow heart. Carruthers (1947), on the other hand, obtained evidence that even in this protein there are cysteine residues other than those involved in the binding of the prosthetic group. It may be that Carruthers's polarographic data are open to other interpretations but further examination of this problem seems desirable. SUMMARY 1. Cytochrome c was prepared from horse heart and purified by chromatography on Amberlite IRC-5O. The product contained 0-46 % of iron and 15-98 % of nitrogen.