| Research Abstract |
Tissue-specific expression pattern of fructose-6-phosphate 2-kinase/fructose 2,6-bisphosphatase (F6P2K) was studied to elucidate a regulation mechanism of glycolysis in skeletal muscle. The F6P2K catalyzes the synthesis and degradation of fructose 2,6-bisphosphate (F26P) which is the most potent activator of glycolysis. The ratio of these activities of the enzyme determines the intracellular content of F26P. Four tissue-specific isozyme genes of the enzyme have been identified in liver, heart, testis and brain. Recently, we have found that the genes produce at least fifteen mRNAs by alternative splicing in a tissue-specific manner. The variety of the enzyme is very important for tissue-specific regulation of glycolysis. In this study we demonstrate the occurrence of nine mRNAs, namely, RM2K, RH2K1, RH2K4, RB2K2, RB2K3, RB2K5, RB2K6, RB2K7 and RB2K8. It is already known that the RM2K is expressed as a protein in skeletal muscle. However, the isoform cannot regulate the glycolysis because it catalyzes the degradation but not the synthesis. Therefore, we prepared antibodies using oligopeptides as antigens to detect each isoform by western blot. Surprisingly, no isoform was detected in skeletal muscle. Interestingly, the RB2K7 isoform was detected only in heart, although the RB2K7 and the RB2K8 mRNAs were expressed in brain, skeletal muscle and heart at the same level. These results indicate that the expression of the RB2K7 and RB2K8 proteins is regulated by translational and/or post-translational processes but not by their mRNA levels.
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