Primary structure of the L subunit of the reaction center from Rhodopseudomonas sphaeroides.

Abstract

The reaction center is an integral membrane protein that, together with several cofactors, mediates the primary photochemical events in bacterial photosynthesis. The amino-terminal sequences of the 3 subunits, L, M and H, of the reaction center protein and the sequence of the structural gene encoding the M subunit were reported previously. The 3'' end of the structural gene encoding the L subunit overlaps by 8 bases the 5'' end of the gene encoding the M subunit. The primary structure of the L subunit was determined from the nucleotide sequence of the gene and from analyses of the amino acid carboxyl termini of the protein. The sequences of a number of trytic and chymotryptic peptides were used to corroborate the nucleotide sequence. The L subunit was composed of 281 amino acids (MW 31,319) and contained 5 hydrophobic segments. It is homologous to the M subunit and to a plant thylakoid protein referred to as the QB or MW 32,000 protein.