Rat and rabbit liver mRNAs code for fructose 1,6-bisphosphatases that differ in molecular weight

Abstract

Summary Fructose 1,6-bisphosphatase was synthesized in vitro using Poly(A)+ RNA isolated from rat and rabbit liver and the specific translation products were identified by immunoprecipitation using antibody raised against the individual purified proteins, followed by electrophoresis on polyacrylamide gels in the presence of sodium dodecyl sulfate. The in vitro synthesis products were found to have subunit molecular weights which were identical to the corresponding purified proteins; 36,000 and 40,000 for the rabbit and rat enzymes, respectively. The rat liver enzyme synthesized in vitro could be converted to a form with a molecular weight nearly identical to that of the rabbit liver enzyme by treatment with trypsin. The results demonstrate that the difference in molecular weight between rat and rabbit liver fructose 1,6-bisphosphatase subunits is not due to limited proteolytic modification of the rabbit liver enzyme during purification. It is proposed that the rabbit liver enzyme in vivo lacks the COOH-terminal phosphorylation site which is present on the rat liver enzyme.