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Abstract:
Using automated procedures for Edman degradation and for the identification of the derived phenylthiohydantoin-amino acids of the cytochrome subunit in the photosynthetic reaction center from the purple bacterium Rhodopseudomonas viridis, the phenylthiohydantoin derivative of the first amino acid could not be detected. However, the N-terminus of the cytochrome subunit was not blocked, and a phe-nylthiohydantoin derivative could be isolated after manual Edman degradation. It contained two kinds of covalently bound fatty acids (18:OHand18:1); the pattern of molecular species obtained by reversed-phase high-performance liquid chromatography and the specific fatty acid composition of the separated species were only consistent with two ester bonds per molecule. Mass spectroscopic analysis provided evidence that the N-terminal amino acid was a cysteine which was linked to a diglyceride via a thioether bond, as has been first described for the N-terminus of the major outer membrane lipoprotein from Escherichia coli [Hantke, K., & Braun, V. (1973) Eur. J. Biochem. 34, 284-296], However, the cytochrome subunit lacked the acylation by a fatty acid at the N-terminal amino group. In addition, the DNA coded for a cysteine as the N-terminal amino acid and for a preceding peptide sequence characteristic for signal sequences of bacterial lipoproteins. The fatty acids seem to anchor the cytochrome subunit in the photosynthetic membrane which is an invagination of the inner bacterial membrane
