The effect of acute salinity stress on the activity of key enzymes of the American oyster, Crassostrea virginica Gmelin.

The enzymatic responses of individual tissues are variable for acute salinity stress. Adductor muscle in all cases exhibited a predominant anaerobic pathway, but concomittant activity of enzymes such as GDH and GOT associated with the citric acid cycle indicated that this pathway, although operative, was at a low level. Gill and to a less degree, mantle had only minor activity in this cycle. Tissues that were subjected to hypoosmotic stress had greater enzymatic responses initially, but the pattern of enzymatic adjustments were quite similar in both acclimating populations. In later acclimating periods, the majority of enzymes in all tissues tended to return to enzyme-substrate affinity levels close to those of the control, which generally followed known patterns of amino acid and substrate change during acclimation. The pivotal role of PK and PEPCK in aerobic- anaerobic transition was indicated by substrate affinity changes in both enzymes, particularly for adductor muscle. Initially in gill, PK changes were similar to the adductor, but in later periods of acclimation, the 8 %. population differed from the 32 %. population. The anaerobic pathway predominated in all three tissues, the levels of activity reflected the metabolic needs of the acclimating organisms and the adjustments made in amino acid levels and substrate utilization.