High levels of citric acid inhibit the enzyme phosphofructokinase, a key enzyme in glycolysis. citric acid binds to the enzyme at a different location from the active site. this is an example of _____. high levels of citric acid inhibit the enzyme phosphofructokinase, a key enzyme in glycolysis. citric acid binds to the enzyme at a different location from the active site. this is an example of _____. the specificity of enzymes for their substrates competitive inhibition positive feedback regulation allosteric regulation