title: Control of D-octopine formation in scallop adductor muscle as revealed through thermodynamic studies of octopine dehydrogenase.
abstract: Octopine dehydrogenase (OcDH) from the adductor muscle of the great scallop, Pecten maximus (Linné, 1758), catalyses the NADH-dependent condensation of l-arginine and pyruvate to d-octopine, NAD(+) and water during escape swimming and subsequent recovery. During exercise, ATP is mainly provided by the transphosphorylation of phospho-l-arginine and to some extent by anaerobic glycolysis. NADH resulting from the glycolytic oxidation of 3-phosphoglyceraldehyde to 1,3-bisphosphoglycerate is reoxidized during d-octopine formation. In some scallops d-octopine starts to accumulate during prolonged, strong muscular work, whereas in other species d-octopine formation commences towards the end of swimming and continues to rise during subsequent recovery. The activity of OcDH is regulated by a mandatory, consecutive mode of substrate binding in the order NADH, l-arginine and pyruvate, as demonstrated by isothermal titration calorimetry. The first regulatory step in the forward reaction comprises the binding of NADH to OcDH with a dissociation constant K(d) of 0.014±0.006 mmol l(-1), which reflects a high affinity and tight association of the apoenzyme with the co-substrate. In the reverse direction, NAD(+) binds first with a K(d) of 0.20±0.004 mmol l(-1) followed by d-octopine. The binary OcDH-NADH complex associates with l-arginine with a K(d) of 5.5±0.05 mmol l(-1). Only this ternary complex combines with pyruvate, with an estimated K(d) of approximately 0.8 mmol l(-1) as deduced from pyruvate concentrations determined in the muscle of exhausted scallops. At tissue concentrations of pyruvate between 0.5 and 1.2 mmol l(-1) in the valve adductor muscle of fatigued P. maximus, binding of pyruvate to OcDH plays the most decisive role in initiating OcDH activity and, therefore, in controlling the onset of d-octopine formation.
authors.affiliation: Institute of Zoophysiology, Heinrich-Heine University, 40225 Düsseldorf, Germany.
authors.forename: Nadine
authors.initials: N
authors.lastname: van Os
authors.forename: Sander H J
authors.initials: SH
authors.lastname: Smits
authors.forename: Lutz
authors.initials: L
authors.lastname: Schmitt
authors.forename: Manfred K
authors.initials: MK
authors.lastname: Grieshaber
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000594:Amino Acid Oxidoreductases / Q000378:metabolism*; D000818:Animals; D001120:Arginine / Q000031:analogs & derivatives* / Q000378:metabolism; D001665:Binding Sites; D002151:Calorimetry / Q000379:methods; D007700:Kinetics; D008956:Models, Chemical; D009068:Movement; D009132:Muscles / Q000378:metabolism*; D009243:NAD / Q000378:metabolism; D049897:Pectinidae; D019289:Pyruvic Acid / Q000737:chemistry; D013379:Substrate Specificity; D013550:Swimming; D013816:Thermodynamics
chemical_list: D009243:NAD; C005394:octopine; D019289:Pyruvic Acid; D000255:Adenosine Triphosphate; D001120:Arginine; D000594:Amino Acid Oxidoreductases; C021903:D-octopine dehydrogenase