Phosphoglycerate kinase isozyme profile in reproductive cells and tissues of cattle: sperm specificity of PGK-B1

Myopathies due to enzyme deficiencies

After the discovery in 1959 of myophosphorylase deficiency, at least 15 myopathies due to deficiency of enzymes involved in energy substrate utilization have been described. In this review two main categories of enzymopathies, glycogenosis and mitochondrial disorders, are discussed. Clinically, the patients with these categories of enzyme defects present two major syndromes: acute recurrent muscle impairment, generally related to exercise, associated with cramps and/or myoglobinuria; progressive muscular weakness and wasting eventually associated with signs of affected organs other than skeletal muscle. Defects of glycogen breakdown and of the first step of glycolysis are more frequently associated with acute exercise intolerance, such as in myophosphorylase and phosphofructokinase deficiencies, but may be associated with progressive muscle weakness and wasting, such as in acid maltase and debrancher enzyme deficiency. Clinical heterogeneity is common in these disorders, but a biochemical explanation for their different clinical expression is still lacking. Defects of the second step of glycolysis, phosphoglycerate kinase, phosphoglycerate mutase and lactate dehydrogenase deficiencies, have been discovered recently and are associated with exercise intolerance. The reason for muscle weakness and atrophy in glycogenosis is still unclear, although it has been suggested that excessive protein catabolism occurs in myophosphorylase, debrancher and acid maltase deficiencies. Myopathies due to deficiencies of mitochondrial enzymes are less well defined, as a group, than the glycogenoses. They are currently considered to fall into three main groups: defects of substrate utilization, such as carnitine palmitoyltransferase deficiency; defects of respiratory chain complexes, such as cytochrome-c-oxidase deficiency and defects of phosphorylation-respiration coupling, such as Luft's disease. Again, severe and benign exercise intolerance or progressive life-threatening myopathic syndromes may be the clinical expression of these disorders. Detailed biochemical and morphological studies of muscle biopsies are needed in these patients to obtain a definite diagnosis and prognosis, and to decide on eventual treatment.

Phosphoglycerate kinase deficiency myopathy: Biochemical and immunological studies of the mutant enzyme

A new phosphoglycerate kinase variant (PGK New Jersey) has been purified from muscle and cultured fibroblasts of a patient with recurrent myoglobinuria. The mutant enzyme had higher than normal affinity for adenosine triphosphate (ATP) and 3-phosphoglycerate, and a shift of the pH optimum towards the acidic side. Antibodies raised against PGK purified from normal muscle were used to evaluate the presence of immunologically cross-reacting enzyme protein in tissues from the patient. Immunodiffusion and an antibody consumption test showed the presence of reduced amounts of cross-reacting material in the patient's muscle. Several PGK variants have been characterized in asymptomatic individuals or in patients with hemolytic anemia. The biochemical features of PGK New Jersey, the only known variant associated with recurrent myoglobinuria, distinguish this mutant enzyme from others.