futile cycle

(redirected from substrate cycle)

fu·tile cy·cle

a cycle of phosphorylation and dephosphorylation catalyzed by two enzymes that normally function in two different metabolic pathways; the net effect is the hydrolysis of ATP and the generation of heat, for example, the futile cycle from the unregulated action of 6-phosphofructokinase and fructose-1,6-bisphosphatase in muscle; such cycles may have an important role in heat production, in the fine-tuning of the regulation of certain pathways, and may be a factor in malignant hyperthermia.
Synonym(s): substrate cycle
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