Influence of molting and starvation on the synthesis of proteolytic enzymes in the midgut gland of the white shrimp Penaeus vannamei.

We investigated the effect of starvation as a stimulant of the digestive system on digestive proteinase activities in the white shrimp Penaeus vannamei. The starved organisms were sampled periodically according to the molting stage and compared with a continuously fed group. Molting stage was included as an independent variable. Most analyzed variables, except for trypsin, were more affected by starvation than by molting, indicating that starvation is a stimulant that masks the effect of molting and showing that food or alimentary stress is more conspicuous than physiological ones. We found that starvation is a stimulant that surpasses the effect of molting, and because it affects the activity of digestive proteinases, studies of starving organisms in combination with tools of molecular biology, can be a helpful working model in the understanding of mechanisms of regulation of digestive enzyme activity. In the starved organisms, trypsin and chymotrypsin activities were similar, suggesting dependence of one to the other. Changes in proteolytic activities and the number of protein bands in electrophoresis showed evidence of synthesis regulation in the midgut gland of white shrimp.