Living with water stress: evolution of osmolyte systems.

Striking convergent evolution is found in the properties of the organic osmotic solute (osmolyte) systems observed in bacteria, plants, and animals. Polyhydric alcohols, free amino acids and their derivatives, and combinations of urea and methylamines are the three types of osmolyte systems found in all water-stressed organisms except the halobacteria. The selective advantages of the organic osmolyte systems are, first, a compatibility with macromolecular structure and function at high or variable (or both) osmolyte concentrations, and, second, greatly reduced needs for modifying proteins to function in concentrated intracellular solutions. Osmolyte compatibility is proposed to result from the absence of osmolyte interactions with substrates and cofactors, and the nonperturbing or favorable effects of osmolytes on macromolecular-solvent interactions.

Metabolism of trimethylamines in kelp bass (Paralabrax clathratus) and marine and freshwater pink salmon (Oncorhynchus gorbuscha).

3H or 14C labeled tracers were used to investigate the metabolism of trimethylamine (TMA), trimethylamine oxide (TMAO), choline, and betaine in free swimming kelp bass (Paralabrax clathratus). An indwelling cannula in the ventral aorta was used to administer tracer and with-draw blood samples. The concentrations of TMA and TMAO were determined in liver, muscle, and plasma. The TMA liver content is higher than that of muscle (0.85 vs less than 0.01 mumoles/g wet tissue) while the amount of TMAO in muscle greatly exceeds its liver concentration (60 vs 0.04 mumoles/g wet tissue). Prolonged fasting (21 and 75 days) or feeding the fish a squid diet containing high levels of TMAO did not alter the tissue concentrations of TMA or TMAO, suggesting that these compounds are endogenous in origin and that their tissue concentrations are subject to regulation. Comparison of the radiospecific activities of TMA and TMAO, and the administered TMA tracer suggest that TMA is channeled directly to TMAO in the liver without equilibration in the hepatic TMA pool. The conversion kinetics of TMA to TMAO and the distribution of these amines in liver and muscle with time suggest that labeled TMA is rapidly taken up into a sequestered pool from which it is slowly released, oxidized to TMAO in the liver, and then transported via the circulation to the muscle mass. The location of this proposed sequestered TMA pool was not determined. Experiments with labeled choline and betaine suggest that these compounds are interconverted in the liver and that enzymes are present for conversion of choline in equilibrium betaine----TMA----TMAO. Labeled dimethylamine (DMA) was not metabolized and is, therefore, probably not a precursor of TMA and TMAO. [14C]Trimethylamine (TMA) was also used to investigate the possible role of trimethylamine oxide (TMAO) as an osmoregulatory compound in migrating prespawning cannulated Pacific pink salmon (Oncorhynchus gorbuscha) taken from marine or fresh water environments. Marine and fresh water salmon oxidized administered [14C]TMA to TMAO; labeled metabolites other than TMA and TMAO were not detected. Four hours after [14C]TMA injection about 10% of the administered dose was present in muscle as labeled TMAO and about 33% as TMA. Unlike our finding in kelp bass, [14C]TMAO was not recovered in liver, although low amounts of labeled TMA were found (0.4% of administered dose). Labeled TMA and TMAO, however, were detected in liver after [14C]betaine administration to a marine salmon, indicating that TMA-mono-oxygenase is present in salmon liver.(ABSTRACT TRUNCATED AT 400 WORDS)