Abstract
1. 1. The kinetic properties of turtle [ Pseudemys ( Chrysemys) scripta elegans] ventricle phosphofructokinase (PFK) were examined. 2. 2. At pH 7·28, PFK demonstrates a high degree of co-operativity with respect to F-6-P. This co-operativity is enhanced with increased ATP concentration or addition of citrate and is reduced by addition of ADP at 0·2 mM or by decreasing H + concentration. 3. 3. The enzyme shows a hyperbolic activity curve with respect to ATP; however, increased ATP or addition of citrate inhibits the enzyme. Increased pH, F-6-P concentration, enzyme concentration, addition of ADP or 5′AMP at 0·2 mM, or maintaining the Mg 2+ and ATP concentration equal, reduces ATP inhibition. 4. 4. At 2·5 mM ATP, PFK is activated by Pi, 5′AMP and ADP, but ADP loses its capacity to activate at ADP concentrations above 0·5 mM. 5. 5. At 1·0 mM ATP, PFK is inhibited by citrate and ADP. 5′AMP activates less at 5′AMP concentrations greater than 0·1 mM, while Pi has no effect. Citrate inhibition is decreased by a high F-6-P concentration (3·0 mM).
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