Response of the phosphofructokinase and pyruvate kinase genes expressed in the midgut gland of the Pacific white shrimp Litopenaeus vannamei during short-term starvation

Crustaceans commonly experience starvation periods due to natural food scarcity and during molting. Several physiological, metabolic and behavioral changes have been associated with starvation in these animals. Traditionally, protein was assumed as the main energy source for crustaceans; however, new findings indicate that carbohydrates reserves in shrimp are the first source of energy used during short-term fasting. As carbohydrate metabolism might be more important than previously assumed, analysis of the effect of starvation could bring new insights to understand the physiology of nutrition in crustaceans. We report a partial cDNA sequence of phosphofructokinase (PFK) and three different pyruvate kinase (PK) sequences from the white shrimp Litopenaeus vannamei. The predicted proteins contain the highly conserved regions necessary for binding the respective substrates. Expression of PFK and PK is tissue-specific. PFK is more abudant in midgut gland while PK is in muscle. To contribute to the knowledge of glucose utilization, the expression levels of midgut gland PFK and PK under short-term starvation were evaluated using qRT-PCR. PFK transcripts abundance significantly increased after 96 h starvation as previously shown for midgut gland glycogen, while PK did not. This could suggest that in the midgut gland PFK responds directly to stored glycogen, while PK remains active probably due to the entrance of other metabolites to the glycolytic pathway.