HETEROGENEOUS N-ACYLATION IS A TISSUE-SPECIFIC AND SPECIES-SPECIFIC POSTTRANSLATIONAL MODIFICATION

Heterogeneous N-terminal glycine acylation recently has been reported for two proteins involved in visual signal transduction. Similar N-acy lations have typically involved only myristate; however, none of the p reviously examined proteins were isolated from retinas. To determine w hether heterogeneous N-acylation is tissue-specific or protein sequenc e specific, the N-terminal modifications of the catalytic subunit of c AMP-dependent protein kinase, partially purified from bovine retinas, heart, and brain tissues, were characterized. Using tandem mass spectr ometry and liquid chromatography coupled directly to an electrospray m ass spectrometer, we found only myristate at the N termini of catalyti c subunits from brain and heart tissue, whereas the N termini of the r etina-derived subunits were heterogeneously acylated in a manner simil ar to recoverin and transducin. Thus it appears that the nature of N-t erminal glycine acylation is determined by the cell or tissue type in which it is located, and not by the sequence of the modified protein. We also examined the N-acylation of recoverin purified from human reti nas, as well as transducin purified from frog retinas, to determine if heterogeneous acylation of retinal proteins is a uniquely bovine phen omenon. Interestingly, human recoverin was modified by the same family of fatty acids found on the bovine retinal proteins, while frog trans ducin was modified homogeneously not with myristate, but with a doubly unsaturated (C14:2) fatty acyl group.