Antibodies against the carboxyl-terminal 5-kDa peptide of the alpha subunit of transducin crossreact with the 40-kDa but not the 39-kDa guanine nucleotide binding protein from brain.

Abstract

Antisera (18) showing reactivity against the .alpha. subunit of transducin, the guanine nucleotide binding protein from rod outer segment, were tested for crossreactivity against the 40- and 39-kDa [kilodalton] guanine nucleotide binding proteins purified from bovine brain. A single antiserum, CW6, showed crossreactivity, and this was predominantly against the 40-kDa protein. Immunoblots of the tryptic fragments of transducin .alpha. subunit with multiple antisera raised against that subunit showed that only CW6 recognizes a COOH-terminal 5-kDa peptide that includes the site of pertussis toxin ADP-ribosylation. Antibodies against the 5-kDa peptide, affinity-purified from CW6, specifically react with the 40-kDa brain protein on immunoblots. The 39- and 40-kDa guanine nucleotide binding proteins from brain differ immnochemically and that the COOH-terminal 5-kDa peptide of transducin .alpha. subunit is homologous to a region in the 40-kDa brain protein. This homologous region may be in a domain that confers specificity for receptor interactions of guanine nucleotide binding proteins.