Ionic requirements for chitinase/chitobiase activity in the oyster, Crassostrea virginica

1. 1. Chitinase/chitobiase activity in the crystalline style of the American oyster was examined over a 0–35‰ salinity range and in media of varying ionic composition. 2. 2. When tested singly, Ca 2+ tended to inhibit enzyme activity at 0.5–2 mmol/1, but was stimulatory at concentrations higher than 2 mmol/1. 3. 3. Magnesium, tested singly, had the opposite effect, although when both divalent cations were tested together, the stimulatory effect of one tended to offset the inhibitory effect of the other. 4. 4. The effect of sodium was slightly inhibitory to style chitinase, at high concentrations. 5. 5. Style chitinase activity in normal sea-water was seen as a result of the inhibitory effect of Na + and Mg 2+ on one hand, and the stimulatory effect of Ca 2+ on the other.