Solute effects on the glycine cleavage system of two osmoconformers (Raja erinacea and Mya arenaria) and an osmoregulator (Pseudopleuronectes americanus)

Abstract

AbstractThe effects of several organic solutes on the activity of the mitochondrial enzyme complex known as the glycine cleavage system (GCS) were examined in two osmoconforming species (soft‐shelled clam, Mya arenaria and little skate, Raja erinacea) and an osmoregulator (winter flounder, Pseudopleuronectes americanus). Taurine, beta‐alanine (BALA), and proline, compatible solutes which typically have no effect on enzyme function, significantly affected GCS activity with pronounced interspecific differences in sensitivity evident. Urea had no effect on skate GCS activity but significantly inhibited the enzymes from clam and flounder. The methylamines, trimethylamine oxide (TMAO) and betaine, did not significantly affect GCS from any species examined. Sarcosine significantly inhibited GCS from all three species, although this response may be of a regulatory nature. Inhibition of flounder GCS by urea was overcome by TMAO when these solutes were added in a 2:1 ratio (urea:TMAO). Pronounced inhibition of skate GCS occurred in response to urea + TMAO (2:1), whereas neither solute added alone had an effect on GCS activity. Although significant interspecific differences in solute effects occurred, each osmoconforming species was less sensitive to its own native osmolytes. BALA, however, stimulated skate GCS and may be important in enhancing sarcosine oxidation during hypoosmotic stress. The potential physiological significance and biochemical implications of these solute effects are discussed.