Some digestive carbohydrases from the midgut gland of Penaeus indicus and Penaeus vannamei (Decapoda: Penaeidae)

Digestive (midgut) gland homogenates from wild specimens of Penaeus indicus from the Kenya coast, as well as from laboratory-reared P. indicus and Penaeus vannamei, were assayed for several key carbohydrate digesting enzymes. The pH optima at 30 °C for the various enzymes all fell within the pH range 5.0-8.0. The highest total amylase (amylase + maltase) activity was observed around pH 6.1 for both laboratory specimen types and at pH 5.2 for wild shrimp. Maltase activity was greatest between pH 5.0 and 7.0 in P. indicus and between 6.0 and 7.0 in P. vannamei. The pH optimum for a-glucosidase was around 6.0 for both P. indicus and P. vannamei. The pH optima (7.0-8.0) for specific a-amylase were similar in both species. The activities of ß-glucosidase and laminarinase were assayed in wild shrimp and were found to have pH optima of 5.5 and 7.0, respectively. Whereas the highest measured specific activities of specific a-amylase and maltase were similar between the two species, the activity of a-glucosidase was slightly higher (0.05 µmol glucose/mg protein/min against 0.02-0.03 U) and that of total amylase significantly lower in P. vannamei (0.07 U) than in P. indicus (> 0.45 U). 26% of the laminarinase and 30% of the ß-glucosidase activities remained in the pellet fraction following centrifugation. The other enzymes were entirely within the soluble fraction. © 1995.