ISOFORMS OF FATTY-ACID-BINDING PROTEIN IN BOVINE HEART ARE CODED BY DISTINCT MESSENGER-RNA

In the course of our studies on structure/function relationships of fa tty-acid-binding proteins, we reported earlier that the two isoforms o f the 15-kDa cardiac fatty-acid-binding protein (cFABP) from bovine he art only differ in one position; Asn98 in pI 5.1-cFABP; Asp98 in pI 4. 9-cFABP [Unterberg, C., Borchers, T., Hojrup, P., Knudsen, J. and Spen er, F. (1990) J. Biol. Chem. 265, 16 255-16 261]. In the present study , we elucidate the origin for this heterogeneity. Isoelectric focusing analysis of immunoprecipitated in vitro translation products from tot al mRNA and positive-hybrid-selected cFABP/mRNA revealed two L-[S-35]m ethionine-labeled proteins corresponding to pI 5.1-cFABP and pl 4.9-cF ABP. In a control experiment, recombinant mRNA derived from cDNA encod ing pI 5.1-cFABP was translated and produced only pI 5.1-cFABP as show n by isoelectric focusing of the translation products. We could observ e co-translational acetylation but not post-translational deamidation of the cFABP isoforms. Taken together, our results demonstrate that th e isoforms of cardiac fatty-acid-binding protein found in bovine heart are coded by distinct mRNA species.