Solute compatibility with enzyme function and structure: Rationales for the selection of osmotic agents and end‐products of anaerobic metabolism in marine invertebrates

Abstract

The major nitrogenous osmolytes present in the cells of marine invertebrates, notably the free amino acids glycine, alanine and proline, and trimethylamine oxide and betaine, are highly compatible with proper enzyme function and structure. These nitrogenous osmolytes display either non-perturbing or, in some cases, favorable effects on enzyme-substrate and enzyme-cofactor complex formation, catalytic velocity and protein structural stability. In contrast, inorganic salts (KCl and NaCl) and certain of the free amino acids which play only a minor osmotic role, e.g., arginine and lysine, have strongly perturbing effects on one or more of these enzymic parameters. The compatible nitrogenous solutes therefore are suitable for use at high (several tenths molar) concentrations and at widely varying concentrations in osmo-conforming species. Certain nitrogenous solutes, especially trimethylamine oxide, betaine and glutamate, offset some of the perturbing effects of inorganic ions on enzyme function. The selective accumulation of osmolytes thus involves not only the concentration of non-perturbing solutes, but also a balanced accumulation of solutes with opposing effects on enzymes. The selection of end-products of anaerobic metabolism also appears to be based, in part, on considerations of solute compatibility with enzyme function. Octopine is a non-perturbing solute, whereas arginine, which is condensed with pyruvate to form octopine, is very strongly perturbing. Succinate has marked stabilizing effects on protein structure. We conclude that the composition of the intracellular fluids of marine invertebrates reflects selection for osmolytes and end-products whose net effects create a cellular microenvironment which is conducive to optimal enzyme function and structure. The accumulation of compatible solutes may preclude the necessity for widespread changes in protein structure in adapting to concentrated or highly variable osmotic environments.

Pure Egyptian Cattle Bulls Show both Individual Variation and Different Interaction with Extender in the Post-Thawing Sperm Parameters

“…The role of glycine in the protection of sperm during freezing-thawing process still not clear but many authors explain a suspected role in protection, as free amino acids and quaternary nitrogen containing compounds retard thermal denaturation of enzymes or provide thermal protection or maintain enzyme structure and function [42][43][44].…”

Using the critical salinity (S crit) concept to predict invasion potential of the anemone Diadumene lineata in the Baltic Sea

“…Inorganic ions are typically used in response to short-term and rapid changes in external osmolarity, while organic osmolytes are utilized during long-term acclimation (Silva and Wright 1994). Compatible organic osmolytes have the advantage of not interacting with intracellular metabolism, whereas inorganic ions and certain amino acids can have strong perturbing effects on vital functions, such as cellular enzymatic reactions (Bowlus and Somero 1979). Thus, osmoconformers employ a variety of cellular regulatory mechanisms to maintain relatively constant concentrations of intracellular inorganic ions when external salinity fluctuates.…”

On the role of surface tension in the stabilization of globular proteins

“…A similar lack of correlation has also been found for MgC12 (Arakawa et al, 1990). Furthermore, in their study of the effects of osmolytes on the thermal stability of RNaseA, Bowlus and Somero (1979) found that all of the intracellular solutes they tested stabilized RNaseA structure, except for ArgHC1, which decreased the transition temperature of the protein. Because ArgHCl and LysHCl have the potential to interact directly with proteins, e.g., by hydrogen bonding to peptide groups, it was proposed that the measured preferential interactions are a summation of the effects of the increase in surface tension and weak binding (Kita et al,1 994).…”