Comparative study of free and bound glycolytic enzymes from sea scorpion brain

Free and bound forms of hexokinase, pyruvate kinase, and lactate dehydrogen ase were prepared from the brain of the sea scorpion (Scorpaena porcus) in a low ionic strength medium. Properties of the free and bound forms were co mpared to determine whether binding to particulate matter could influence e nzyme function or stability in vivo. Changes in pH differently affected the activity of the free and bound forms of all three enzymes. Furthermore, bo und forms of hexokinase and pyruvate kinase were more stable than the free enzymes to heating at 45 degrees C. Bound hexokinase showed higher affinity for substrates (ATP, glucose) than the free form and bound lactate dehydro genase had greater affinity for pyruvate and NADH. Although the affinities of the two forms of pyruvate kinase for substrates were similar, Hill coeff icients for phosphoenolpyruvate as well as inhibition by ATP differed betwe en the two enzyme forms. Free and bound lactate dehydrogenase also showed d ifferences in Hill coefficients and bound lactate dehydrogenase was less se nsitive to substrate inhibition by high pyruvate concentrations. The possib le physiological role of the binding of these glycolytic enzymes to subcell ular structures is discussed.