Mechanisms of glycolytic control during facultative anaerobiosis in a marine mollusc: tissue-specific analysis of glycogen phosphorylase and fructose-2,6-bisphosphate

Changes in the activity of glycogen phosphorylase and the content of fructose-2,6-bisphosphate (F-2, 6-P2) were monitored in tissues of the whelk, Busycotypus canaliculatum, over a 21-h course of environmental anoxia. Tissue-specific responses to anoxia were seen with respect to phosphorylase content: in the radular retractor muscle and foot, the content of phosphorylase a expressed rose rapidly over the initial hours of anoxia (maximal increases were 4.3- and 2.5-fold, respectively) while in the gill, content dropped 2-fold during anoxia. Phosphorylase content was modulated by two mechanisms, changes in the percentage of enzyme in the active a form and changes in the total amount (a + b) of enzyme expressed. Anoxia stimulated a dramatic reduction in F-2,6-P2 content in five tissues. In the ventricle, content fell by 224-fold with a t1/2 of only 35 min. Levels in gill, radular retractor, hepatopancreas, and kidney fell to 2.5–3.5% of control values within the first 8 h of anoxia. F-2,6-P2 content in foot muscle was not altered during anoxia. Changes in glycogen phosphorylase activities and F-2,6-P2 contents help to produce tissue-specific responses of glycolysis to environmental anoxia that acknowledge competing metabolic demands including metabolic rate depression, changes in fuel use, anaerobic energy needs, and carbohydrate use for anabolic purposes.