REGULATORY PROPERTIES OF 6-PHOSPHOFRUCTO-1-KINASE OF THE MIDGUT OF THE GRASSHOPPER, POEKILOCERUS-BUFONIUS

The fine structure of the mid-gut of Poekilocerus bufonius has been examined and three types of epithelial cells were identified; normal epithelial cells with their apical part possessing well developed microvilli, goblet-like cells containing myelin-like figures and the small basal cells with small and round nuclei, nidi. The regulation of 6-phosphofructo-1-kinase (PFK-1) prepared from the mid-gut of the grasshopper, Poekilocerus bufonius, was studied. Mid-gut PFK-1 displayed cooperativity with respect to fructose-6-phosphate at pH 7.0, and the enzyme was inhibited by high concentrations of ATP. The affinity of the enzyme for fructose-6-phosphate was increased by fru-2,6-P2 whereas the inhibition of the enzyme by high concentrations of ATP was relieved by fru-2,6-P2. The activity of mid-gut PFK-1 was highly stimulated in a simultaneous presence of low concentrations of fru-2,6-P2 and AMP. ADP, AMP and c-AMP were all shown to be activators of the mid-gut PFK-1 with AMP being the greatest effector. The enzyme was not inhibited by citrate either in the presence of low or high concentrations of ATP. These results suggest that the PFK-1 of the mid-gut of the grasshopper is highly regulated with positive stimulators, specially fru-2,6-P2, whereas the enzyme is not regulated by citrate or glucose-1,6-bisphosphate. © 1990.