Characterization of the enzymatic lesion in inherited phosphofructokinase deficiency in the dog: an animal analogue of human glycogen storage disease type VII

Abstract

Mammalian phosphofructokinase (PFK; ATP:D-fructose-6-phosphate 1-phosphotransferase, EC 2.7.1.11) exists in multimolecular forms, which result from random tetramerization of three distinct subunits, M (muscle-type), L (liver-type), and P (platelet-type), each under a separate genetic control. Human muscle and liver contain homotetramers M4 and L4, respectively, whereas erythrocytes contain a mixture of M4, M3L, M2L2, ML3, and L4 isozymes. Homozygous deficiency of the M subunit in man results in glycogen storage disease (GSD) type VII, which is characterized by exertional muscle weakness and compensated hemolysis; the residual erythrocyte PFK consists of isolated L4 isozyme. Recently, PFK deficiency associated with isolated hemolytic anemia has been identified among English springer spaniel dogs. We investigated the genetic control of the dog PFK system and the nature of the enzymatic defect in two PFK-deficient animals, using chromatographic and immunological techniques. Our studies indicate the existence of a trilocus isozyme system for the dog, as is the case with other mammals. Muscle PFK consists of M4 isozyme, whereas the predominant species of liver and platelet consists, respectively, of the L4 and P4 isozyme; erythrocyte PFK consists of a three- or four-membered set composed of M and P subunits. PFK deficiency in the dogs was found to result from a total and universal lack of the M subunit, as is the case in man. However, the probands consistently exhibited L4 isozyme in their muscle; P4, L4, and hybrids thereof in their erythrocytes; and an increase in the L-containing isozymes in their platelets, indicating a generalized anomalous presence of the L subunit. The apparent absence of muscle disease in these animals is most likely accounted for by both the well-known high oxidative potential of the canine muscle in general and the presence of liver PFK in the M-deficient muscle in particular. In contrast, presence of hemolysis despite residual P4 and hybrids of P and L in the erythrocytes may be inferred to result in severe glycolytic handicap under existing intraerythrocytic conditions.