Studies of Cytochrome b-555 from Larvae of the Housefly, Musca domestica L.***

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Abstract
A crude larval cytochrome b-555 preparation was separated into two or three components by the method of isoelectric focusing. The two main components had much the same or the same absorption spectra, catalytic activity, molecular weight, amino acid composition, and circular dichroic spectra in the Soret region. For three components the pI values at 0–2°C were 4.24, 4.28, and 4.32, respectively. A number of explanations was suggested for the heterogeneity of larval cytochrome b-555. The circular dichroic spectra of ferri- and feirocytochrome b-555 suggested that the protein moiety of the molecule provided an asymmetrical environment to all of the chromophores in the molecule. With respect to the sign of the CD peak in the Soret region of hemoproteins containing protoheme several hypotheses were presented. The amino acid composition of larval cytochrome b-555 was as follows: Lys5, His2, Arg2, Asp10, Thr2, Ser4, Glu1, Pro1, Gly4, Ala5, Val6, Met1, Ile2, Leu2, Tyr2, Phe3. The contents of tryptophan, cysteine and amide were not determined. In comparison with cytochromes b5 from various sources larval cytochrome b-555 contained the fewest amino acid residues (65 amino acid residues other than tryptophan and cysteine), lower contents (%) of histidine, and leucine, and higher contents (%) of alanine and valine.

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