Parameters controlling opine formation during muscular activity and environmental hypoxia

Summary

In order to elucidate the regulatory parameters which determine multiple opine formation in marine invertebrates, anaerobiosis was induced in 25 species from several phyla by stimulating the animals to vigorous muscular activity or by subjecting them to environmental hypoxia. The quantity of glycolytic end products and the corresponding amino acids were measured. In a second set of experiments the amounts of substrates and products of the opine dehydrogenase reactions in the isolated introvert retractor muscle (IRM) ofSipunculus nudus were determined in both situations.

During environmental hypoxia opines accumulated according to the contents of the corresponding amino acids. Mass action ratios (MAR) of the opine dehydrogenase reactions in the isolated IRM were in the range of control values (octopine dehydrogenase 1.9·10¹¹ mol⁻²·l², strombine dehydrogenase 2.2·10¹⁰ mol⁻²·l²). During muscular activity those opines accumulated preferentially which corresponded to the highest opine dehydrogenase activities. In the isolated IRM only octopine accumulated during contractile activity; the MAR of the octopine dehydrogenase reaction was near the control value while the MAR of the strombine dehydrogenase reaction deviated by a factor of 9.

The results indicate that during environmental hypoxia the opine dehydrogenases present in a tissue catalyze near equilibrium and the relative amount of opines accumulated is dictated by the concentration of the corresponding amino acids. During muscular activity only those opine dehydrogenases catalyze near equilibrium which are present in sufficiently high activities to keep pace with an increased glycolytic flux. Therefore, different opines may accumulate in the same animal during muscular activity and during environmental hypoxia.