A novel gene encoding four isozymes of 6-phosphofructo-2-kinase/ fructose-2,6-bisphosphatase expressed in human brain

A novel human gene for 6-phosphofructo-2-kinase/fructose-2,6- bisphosphatase has been identified, that encodes at least four isoenzymes in brain. Localized to chromosome 10spl3, the gene is approximately 60 kb in length and composed of 16 exons and intervening introns. The locations of introns within the protein-coding sequence are identical to those of the enzymes from heart, liver and testes. The different mRNA species are generated from 2 alternative first exons and 3 alternative last exons, with common exons 2 through 14. The latter code for the enzyme catalytic core, that is highly homologous with the cores of other bifunctional enzyme isoforms; containing all of the residues implicated in substrate binding and catalyses. In addition, two of the alternative 3'- exons encode sequences with multiple potential phosphorylation sites, and one encodes a Src homology 3 (SH3) binding motif. The structure is consistent with variable regulatory domains flanking the two catalytic domains. Messenger RNA analyses show that the gene is expressed in almost all brain tissues tested, as well as in intestine and pancreas. Phosphorylation of two of the recombinant isoenzymes, catalyzed by cAMP-dependent protein kinase activated the kinase and inhibited the bisphosphatase.