Fosfofruktokinaza i kinaza pirogronianowa w tkankach skorupiaków i owadów

Abstract

Molecular and kinetic properties of phosphofructokinase and pyruvate kinase of crustacean midgut gland, hypodermis, muscle and heart as well as of insect fat body and flight, body wall and heart muscles have been characterized and compared. The results suggest that the reaction catalyzed by the phosphofructokinase is the most important point for glycolysis regulation in all studied tissues. The phosphofructokinases exist in different interconvertible molecular forms and their activity is regulated by several positive and negative effectors. It is suggested that fructose-2,6-bisphosphate is the most powerful one and it plays a role of the signal which turns the glycolysis on. The pyruvate kinase is also a regulatory enzyme but only in those tissues for which gluconeogenesis is postulated, that is in the crustacean midgut gland and hypodermis as well as in the insect fat body. In these tissues, the enzyme is found in different molecular forms, which are characterized by higher or lower activity in different physiological stages of the tissue. A mechanism of interconversion between them has been explained and the existence of forms of lower activity has been connected with those stages for which gluconeogenesis operation is expected. In strictly glycolytic tissues like crustacean abdominal muscle or insect flight muscle, pyruvate kinase exists in a singular molecular form of high activity. The role of the phosphofructokinase and pyruvate kinase in the carbohydrate metabolism regulation of particular tissues is discussed.