Abstract
The effects of 4 hours and 8 hours of exposure to air on the kinetic properties of phosphofructokinase (PFK) and the maximal activity of glycogen phosphorylase were studied in order to evaluate the role of these enzymes in glycolytic rate control and metabolic depression during air exposure of Patella caerulea foot muscle.
Air exposure resulted in stable modifications of the kinetic properties of PFK including changes in S~0.5~ for fructose‐2,6‐phosphate (fructose‐6‐P), Hill coefficient, K~a~ values for adenosine monophosphate (AMP), fructose‐2,6‐biphosphate (fructose‐2,6‐P~2~), and I~50~ for adenosine triphosphate (ATP) and phosphoenolpyruvate (PEP), the direction of changes being generally consistent with the production of a less active form in the air exposed tissue. Air exposure did not affect maximal activity of glycogen phosphorylase nor the percentage of active α form. In contrast, changes in the tissue content of fructose‐2,6‐P~2~ were observed.
Incubation of PFK preparations with protein kinase second messengers (cyclic adenosine mono‐phosphate [cAMP] and cyclic guanosine monophosphate [cGMP]) lead to an increase in the enzyme activity and affinity for the substrate whereas treatement with alkaline phosphatase reversed these effects. The data suggest that modification of PFK kinetics during air exposure is probably mediated via a phosphorylation‐dephosphorylation mechanism.