The effects of parasitism by Perkinsus marinus on the free amino acid composition of Crassostrea virginica mantle tissue
Seventeen free amino acids were detected from oyster mantle tissue. Taurine, serine (serine plus asparagine and gultamine), glutamic acid, glycine, alanine, and beta-alanine, were found in concentrations greater than 30umol/g dry weight. Moderate concentrations (10 to 30 umol/g. dry weight) of aspartic acid and arginine were detected. Theonine, valine, methionine, isoeucine, leucine, tyrosine, phenylalinine, lysine, and histidine occurred in concentrations of less than 10 umol/g dry wt. This study corroborates the usefulness of the taurine-glycine ratio as a biochemical measure of stress. The close relationship between this ratio and level of parasitism suggests that P. marineus may be the agent of stress. Taurine and aspartic acid concentrations increased with increasing parasitism by Perkinsus marinus; the concentrations of glycine, alanine, isoleucine, leucine, beta-alanine, arginine, and total free amino acids decreased with increasing parasitism. Ratios of specific free amino acids with taurine showed a closer correlation with the level of parasitism than similar correlations of parasitism with individual amino acids. A correlation between the level of parasitism by P. marinus and the molar ratio of taurine-to-glycine showed a particularly close relationship (r=0.90, P<0.001).