The Regulatory Role of Muscle Pyruvate Kinase in Carbohydrate Metabolism of Invertebrates: A Comparative Study in Catalytic Properties of Enzymes Isolated from Tubifex tubifex (Oligochaeta) and Tenebrio molitor (Coleoptera)

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Abstract
Biochemical properties of the pyruvate kinases (PK) isolated from body-wall tissue of Tubifex tubifex (Oligochaeta) and from larvae of the tenebrionid beetle Tenebrio molitor (Coleoptera) have been investigated. Tubifex PK was characterized by sigmoidal kinetics with phosphoenolpyruvate (PEP) in the presence of Mg²⁺ and by allosteric regulation under the influence of energy charge and fructose-1,6-diphosphate (FDP). No significant effects of alanine were found. In the presence of Mn²⁺, hyperbolic substrate saturation curves were obtained. Tenebrio PK showed hyperbolic kinetics with PEP which were not modified by divalent cations and FDP. Tubifex and Tenebrio PKs display values near 2 at saturating PEP concentrations. The Tubifex enzyme is less thermally stable than the Tenebrio enzyme, a distinction observed between other regulatory and nonregulatory PKs. The regulatory role of Tubifex PK in aerobic/anaerobic transitions is discussed relative to the different regulatory properties found for this PK compared with PKs from other facultatively anaerobic invertebrates.