Carbohydrases of the crystalline style of the brackish water clam Rangia cuneata

Abstract

Carbohydrases of the crystalline style of the mactrid Rangia cuneata, from three ecologically different locations on the Texas Gulf coast were studied. Style extracts of Rangia from three populations, Trinity Bay, Lake Anahuac and the Neches River, were found to be capable of cleaving soluble starch, glycogen, dextrin, maltose and carboxymethyl cellulose-fine. The style amylases which cleaved soluble starch and dextrin were shown to be Cl� dependent, while the other carbohydrases were not. The amylases of all three populations required a different Cl� concentration to exhibit maximum activity, the Neches River clam enzymes requiring 3-5 times more than the other populations. At pH's below 5.0 none of the populations exhibited detectable amylase activity. The optimum pH for maximum activity for preparations of all three populations was reached at pH 6.6 with phosphate buffer and activity was completely lost above pH 8.0. Citrate, acetate and succinate buffers exerted an inhibitory effect upon style amylase activity. No style amylase activity was noted for any of the populations when reaction mixtures were incubated at 0 C. The activity increased sharply with increasing incubation temperature until the optima were reached; 30 C for the Neches population and 37 C for both the Trinity and Anahuac populations. All activity was lost with incubation temperatures above 60 C. Exposure of the enzyme preparations to a temperature of 50 C for a period of 16 minutes resulted in approximately 95% loss of amylase activity and all activity was lost after exposure to 65 C for 16 minutes. Exposure of the enzyme preparations to a temperature of 70 C for 4 minutes or 75 C for 2 minutes resulted in complete loss of maltase activity. Amylase activity was noted to be completely inhibited by addition of the chloride salts of Fe��, Hg��, Sn��, Ni�� and Zn��; partially inhibited by Co��, Cd��, K�, Cs��, Rb�, Mn++ and Li�; and increased by Ba��, Ca�� and Sr��. The results of this study clearly indicate the presence of distinct maltase and amylase enzymes in the crystalline style of Rangia cuneata, each of which has a characteristic optimum temperature, temperature of denaturation, and one of which (the amylase) has a definite Cl� requirement. The apparent differences between the style enzyme characteristics of the Trinity and Anahuac Rangia strongly suggest that the Trinity and Anahuac clams are, or were at one time, members of the same population, while the Neches clams, are or were of a different heritage, most probably a different race than the other two populations.