A novel small protein associated with a conjugated trienoic chromophore from membranes of scallop adductor muscle: phosphorylation by protein kinase A

Membranes enriched in sarcolemma from the cross-striated adductor muscle of the deep sea scallop have been found to contain a previously undescribed s mall protein of 6-8 kDa that can be released by treatment with organic solv ent mixtures. This proteolipid co-purified with a non-amino acid chromophor e containing a conjugated trienoic moiety. Although common in plants and al gae, such a stable conjugated trienoic group is unusual for an animal cell. The N-terminal amino acid sequence of the protein was XEFQHGLFGXF/ADNIGLQ, which most strongly resembles sequences in the triacyl glycerol lipase pre cursor and the product of the human breast cancer susceptibility gene BRCA 1, but does not show similarity to previously described proteolipids. The p rotein was found to be one of the major substrates in its parent membrane f or the catalytic subunit of protein kinase A, which may imply a regulatory function for this molecule. (C) 1999 Elsevier Science B.V. All rights reser ved.