Control of D-octopine formation in scallop adductor muscle as revealed through thermodynamic studies of octopine dehydrogenase.

Nadine van Os, Sander H J Smits, Lutz Schmitt, Manfred K Grieshaber

Institute of Zoophysiology, Heinrich-Heine University, 40225 Düsseldorf, Germany.

The Journal of experimental biology 2012 May 1

filter terms:

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.

Citation

Nadine van Os, Sander H J Smits, Lutz Schmitt, Manfred K Grieshaber. Control of D-octopine formation in scallop adductor muscle as revealed through thermodynamic studies of octopine dehydrogenase. The Journal of experimental biology. 2012 May 1;215(Pt 9):1515-22