L-Lactate dehydrogenase in the longitudinal muscle of the sea cucumber Sclerodactyla briareus (Echinodermata: Holothuroidea)

The infaunal holothurian Sclerodactyla briareus (Thyone briareus) is able to tolerate exposure to hypoxic conditions for over 2 days. Since the in vitro anaerobic degradation of glucose-U-C¹⁴ by longitudinal muscle preparations leads to an accumulation of labeled lactic acid, it is apparent that lactate dehydrogenase plays a key role during anoxia. Disc electrophoresis resolved one major band of lactate dehydrogenase (LDH) activity in longitudinal muscle extracts. Muscle extracts of s. briareus oxidized L-lactate only, as is the case with most other echinoderms. The apparent Michaelis constants for lactate oxidation and pyruvate reduction are dissimilar from values reported for other marine invertebrates. The LDH activity in this holothurian is higher than the activities reported for other marine invertebrates with the exception of some active, large arthropods. Substrate inhibition of LDH maximal activity occurs at substrate concentrations (pyruvate) exceeding 10 mM, and then to only a minor extent. The characteristics of lactate dehydrogenase from the longitudinal muscle of S. briareus support the hypothesis that it functions to maintain glycolytic flux during prolonged periods of exposure to anoxic or hypoxic conditions.