[Isolation and characteristics of cyanogen bromide peptides of transducin alpha and beta subunits].

The alpha- and beta-subunits of the GTP-binding protein (transducin) from cattle retina were cleaved with cyanogen bromide. 21 peptides covering 90-100% of the amino acid sequence of the alpha- and beta-subunits were isolated from the hydrolyzate. Cyanogen bromide peptides complete or partial amino acid sequence was determined, the results were compared with those by Numa and coworkers [1] and Lochrie et al. [2] at the primary structure of the transducin alpha-subunit deduced from the nucleotide sequence of the cDNA. The structure by Lochrie is shown to differ much from the true structure of the alpha-subunit; probably, the investigators isolated cDNA, corresponding to the gene for some GTP-binding protein homologous to transducin, but not to the gene for the transducin alpha-subunit. The Numa's structure also contains an error. The final primary structure of the transducin alpha-subunit is given. The protein polypeptide chain consists of 349 amino acid residues and has an acetylmethionine residue as the N-terminal residue.