Complete amino acid sequence of flavocytochrome b2 from baker's yeast

Each subunit of baker's yeast flavocytochrome b2 can be selectively cleaved by proteases into two fragments, amino‐terminal fragment α and carboxy‐terminal fragment β. The primary structure of the former has been reported before [Ghrir, B., Becam, A. M. & Lederer, F. (1984) Eur. J. Biochem. 139, 59–74]. The amino acid sequence of the 197‐residue fragment β has now been established. The fragment was cleaved with cyanogen bromide; the three peptides thus obtained were submitted to digestions with Staphylococcus aureus V8 protease, chymotrypsin and trypsin, sometimes after succinylation. The complete fragment was also submitted to tryptic cleavage after citraconylation. Peptides were separated by thin‐layer finger‐printing or high‐pressure liquid chromatography. They were mostly sequenced in a liquid‐phase sequenator. The 511‐residue amino acid sequence of the mature protein is thus completely established. Secondary structure predictions indicate an alternation of helical and extended structure, with a higher percentage of the former. Comparisons with other flavoproteins do not detect any significant sequence similarity.