Acid and alkaline phosphatase activities in the clam Scrobicularia plana: kinetic characteristics and effects of heavy metals.

The acid and alkaline phosphatase activities of the clam Scrobicularia plana have been partially characterised in different organs and tissues (digestive gland, gills, foot, siphon and mantle) and the 'in vitro' effect of heavy metals on both types of enzymatic activity have been analysed. The optimal pH ranged between 4.0 and 5.5 for acid phosphatase activity and 8.5 and 9.5 for alkaline phosphatase activity. The apparent optimum temperature was in the 30-60 degrees range for acid phosphatase activity and in the 30-40 degrees C range for alkaline phosphatase activity. The effect of substrate concentration on enzymatic activities in the tissues showed a good fit to the Michaelis-Menten model. For both types of enzymatic activity, the highest values were found in the digestive gland. The effect of heavy metals was dependent on the tissue analysed. Mercury showed the highest inhibition in the organs/tissues and the parameters Km and Vmax were modified when the inhibitor concentration increased, thus indicating a mixed type of inhibition.