Fructose-1,6-bisphosphatase in Stage VI Frog Oocytes: Evidence for an Active Enzyme in Vivo

The characterization of fructose-1,6-bisphosphatase in stage VI oocytes from the frog Caudiverbera caudiverbera, as well as the in vivo activity, is reported. The enzyme has a subunit molecular weight of approximately 43,500, has an apparent Km value of 17 μM for fructose-1,6-bisP, and is inhibited by substrate concentrations beyond 100 μM. AMP and fructose-2,6-bisP are strong inhibitors of oocyte fructose-1,6-bisphosphatase activity with Ki values of 9 and 2 μM respectively. Inhibition by AMP is cooperative with a nH value of 2.2. In vivo fructose-1,6-bisphosphatase activity was demonstrated by microinjection of [U-14C]- or [6-32P]fructose-1,6-bisP and subsequent chromatographic separation and identification of labeled products. The relevance of these findings for the metabolism of glucose in frog oocytes is discussed.