Fructose-2,6-bisphosphate (Fru-2,6-P2) is the most powerful allosteric activator of 6-phosphofructo-1-kinase (PFK-1) and an inhibitor of fructose-1,6-bisphosphatase (FBPase-1). Due to its antagonistic actions on these enzymes, Fru-2,6-P2 plays a crucial role in governing flux along glycolytic and gluconeogenic pathways [2]. This metabolite has been reported in bovine spermatozoa at a similar concentration to that found in other
Sulfo-NHS-LC-Biotin [3]. The synthesis and degradation of Fru-2,6-P2 is catalyzed by the bifunctional enzyme, 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase (PFK-2). Distinct isoforms of this enzyme have been identified in mammalian tissues [4], [5] and [6]. The isozymes are encoded by four independent genes, Pfkfb1–4 [2]. A specific combination of isozymes can be simultaneously present in a particular tissue, depending on its metabolic requirements. Previously, we cloned a gene specifically expressed in human testis, that corresponds to Pfkfb4 [7], which encodes the testis PFK-2 isozyme (tPFK-2) [8] and [9]. Mouse spermatogonia (GC-1spg) and mouse Sertoli (TM4) cell lines express tPFK-2 and ubiquitous PFK-2, a product of Pfkfb3 gene, respectively [10]. These observations indicate that in adult
testes these two isozymes are expressed in distinct cell types, supporting the idea that the cell-specific isozymes are expressed to adapt their enzymatic properties to the metabolic demand of a particular tissue or cell status.
