3 - Osmolytes and Metabolic End Products of Molluscs: The Design of Compatible Solute Systems

Abstract

This chapter discusses the design of compatible solute systems in relation to osmolytes and metabolic end products of Mollusks. Marine mollusks, like other marine invertebrates, utilize nitrogenous solutes such as free amino acids as the major intracellular osmotic effectors (“osmolytes). The chapter describes the intracellular fluids and the suite of organic osmolytes utilized by the different groups of marine mollusks. The suite of nitrogenous osmolytes present within the cytosol of marine mollusks is similar to that characteristic of other marine invertebrate groups. The similarities among the osmotic systems far outweigh the differences. In all cases, only a few free amino acids make the dominant contribution to the intracellular pool. Alanine, glycine, proline, taurine, and glutamate are typically the dominant species in marine mollusks. The use of compatible nitrogenous solutes by marine invertebrates, certain halophytes, and many salt-tolerant bacteria is a striking example of convergent evolution. A key achievement of the compatible solute strategy of osmotic adaptation is its evolutionary simplicity.