Cloning of cDNAs for Fructose 6-Phosphate Kinase/Fructose 2,6-Bisphosphatase from Frog Skeletal Muscle and Liver, and Their Expression in Skeletal Muscle

Abstract

Frog ( Rana catesbeiana) skeletal muscle (M-type) and liver (L-type) cDNAs of fructose 6-phosphate 2-kinase/fructose 2,6-bisphosphatase were isolated from λgt10 phage cDNA library. The full-length L-type cDNA (1829 bp) encodes a 469 amino acids subunit ( M r 54,800), while the M-type cDNA (1792 bp) encodes 455 amino acids ( M r 52,901). The amino acid sequence of the M-type isozyme is identical to that of the L-type isozyme except for the N-terminus. The N-terminal 30 amino acids of the L-type isozyme are replaced by an unique sequence of 16 amino acids in the M-type isozyme. Both L- and M-type cDNAs were detected also in a λgt10 phage library of skeletal muscle. Relative amount of the M- and L-type mRNAs in skeletal muscle was determined by the reverse transcription-polymerase chain reaction method. The M/L mRNA ratio in frog skeletal muscle shows seasonal variations, being 0.56 / 1 in early summer and 5.3 / 1 in winter. These results suggest that there is a seasonal change in the isozyme composition and that the glycolysis in frog skeletal muscle may be regulated by type of the isozyme synthesized.