Hormonal effects on structure and catalytic properties of fructose 1,6-bisphosphatase.

Abstract

Gluconeogenic conditions, such as administration of triamcinolone or alloxan diabetes, cause the following changes in the molecular structure and properties of rabbit liver fructose 1,6-bisphosphatase (D-fructose-1,6-bisphosphate 1-phosphohydrolase, EC 3.1.3.11): (1) the appearance of traces (about 10%) of a lighter subunit; (2) loss of tryptophan from all of the subunits, including those that show no apparent change in molecular weight; (3) increase in requirement for the positive allosteric effector, histidine; (4) increase in amount of enzyme, but not its specific activity. These changes are identical to those induced by cold or fasting, and are related to increased activities of lysosomal proteases. The results suggest that lysosomes may act as mediators of gluconeogenic stimuli. Certain gluconeogenic conditions (e.g., fasting or prolonged starvation) are known to be associated with the breakdown of protein in peripheral tissues (1) as well as increased proteolytic activity in liver (2). Associated with these generally catabolic conditions are large increases in the activities of hepatic gluconeogenic enzymes (3-5). These effects probably involve the intervention of gluconeogenic hormones, since similar increases in lysosomal activity and gluconeogenic enzymes have been reported following the administration of glucagon and glucocorticoids (6-12).Our previous studies on the changes in structure and function of a key gluconeogenic enzyme, fructose 1,6-bisphosphatase (Fru-P2ase; D-fructose-1,6-bisphosphate 1-phosphohydrolase, EC 3.1.3.11), have suggested that lysosomes may play a specific role in the modulation of the activity of this enzyme. In animals exposed to prolonged fasting we observed not only the increased activity of this enzyme in liver and kidney, but also certain changes in its structure and catalytic properties. Thus the enzyme isolated from livers of fed rabbits was composed of four-identical subunits having a molecular weight of 36,000, each containing a single tryptophan residue, while enzyme purified from livers of fasted animals was devoid of tryptophan and contained traces of a lighter subunit, with molecular weight of approximately 29,000 (6). The enzyme isolated from livers of fasted rabbits also showed greater stimulation by the allosteric effector histidine (13) and by ammonium ions (unpublished observations). These changes appeared to be related to concomitant changes in the activity and subcellular distribution of two specific lysosomal proteases (14, 15).In the present paper we report evidence for identical changes in the structure and catalytic properties of FruP2ase in animals treated with triamcinolone or rendered diabetic with alloxan, and parallel changes in the lysosomal proteases that may be responsible for the structural modifi- Animals. Adult female rabbits weighing 2.8 1 0.1 kg were used. These were farm-grown animals from the local Italian market. All rabbits were fed ad libitum on a balanced diet (Altromin MS/K purchased from Rieper-Bolzan-Italy) and kept at 250 +...

Binding of Adenosine 5'-Monophosphate to Bovine Liver Fructose 1,6-Bisphosphatase

“…The existence of two forms of rabbit liver fructose 1,6-bisphos phatase is well documented (10,19). Although the physiology of gluconeogenesis varies greatly between ruminants and small, monogastric ani mals, such as rabbits (12), differences in the treatment of cattle, particularly prior to slaugh ter, in the United States and England may lead to different forms of bovine liver fructose 1,6-bisphosphatase.…”