The free amino-acids of invertebrate nerve

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Abstract
Aqueous extracts of nerves from 7 spp. of certain marine Crustacea and cephalopod molluscs contained large amts. of aspartic acid, glutamic acid and alanine, plus taurine in some spp. and glycine in others. These amino acids account for over 20% of the dry wt. of the nerves and are almost certainly in free soln. in the axoplasm. The concns. of these amino acids were accurately detd. in 3 species by a micromethod developed for the purpose: paper chromatograms of the nerve extracts were developed with ninhydrin and the amt. of color extracted with steam was estimated photo-electrically. As little as 0.05 [mu] mole of an individual amino acid could be estimated with a standard error of about [plus or minus] 5%. The major inorganic electrolytes in Carcinus maenas nerve were estimated, and balance-sheets were drawn up for the cation-anion and osmotic balances, in both of which the unexplained deficit was small when account was taken of the free amino acids present. The possible functional significance of these amino acids is briefly discussed: it is suggested that the dicarboxylic amino acids function as internal anions to balance the high internal K concn. necessary for nervous conduction and that the other, "neutral", amino acids function as solute species to maintain the high internal osmotic pressure necessary for equilibrium with sea water.