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Abstract: Hexokinase (HK) catalyzes the phosphorylation of glucose, the first rate-limiting step in glycolysis. HKs are a conserved family of tissue-specific isozymes, from which very little is known in marine crustaceans. This study describes the cloning and characterization of the full-length cDNA sequence for HK from the shrimp Litopenaeus vannamei, the theoretical tridimensional protein structure and response to short-term hypoxia. The full-length cDNA is 1872bp long with an open reading frame of 1452bp coding for a protein of 484 amino acids and predicted molecular mass of 53kDa. Highly conserved amino acid residues are present in the glucose, glucose-6-phosphate, ATP and Mg+2 binding sites. Phylogenetic analysis shows that the shrimp HK is closer to invertebrates than to vertebrate HKs. Hypoxia induced HK expression in gills with the concomitant increase in the specific enzyme activity. In muscle, hypoxia decreased HK mRNAs but increased the enzyme activity. Silencing of the hypoxia inducible factor 1 (HIF-1) affected the expression of HK differentially. In gills, silencing of α or β subunits blocked the induction of HK expression and the enzymatic activity, but not in muscle. This suggests the existence of tissue-specific HK isozymes and post-transcriptional and post-translational regulation of HK. [Copyright &y& Elsevier]

Crustaceans overcome osmotic disturbances by regulating their intracellular concentration of ions and osmolytes. Glycine betaine (GB), an osmolyte accumulated in response to hyperosmotic stress, is synthesized by betaine aldehyde dehydrogenase (BADH EC 1.2.1.8) through the oxidation of betaine aldehyde. A partial BADH cDNA sequence from the white shrimp Litopenaeus vannamei was obtained and its organ-specific expression during osmotic stress (low and high salinity) was evaluated. The partial BADH cDNA sequence (LvBADH) is 1103 bp long and encodes an open reading frame for 217 protein residues. The amino acid sequence of LvBADH is related to that of other BADHs, TMABA-DH and ALDH9 from invertebrate and vertebrate homologues, and includes the essential domains of their function and regulation. LvBADH activity and mRNA expression were detected in the gills, hepatopancreas and muscle with the highest levels in the hepatopancreas. LvBADH mRNA expression increased 2–3-fold in the hepatopancreas and gills after 7 days of osmotic variation (25 and 40 ppt). In contrast, LvBADH mRNA expression in muscle decreased 4-fold and 15-fold after 7 days at low and high salinity, respectively. The results indicate that LvBADH is ubiquitously expressed, but its levels are organ-specific and regulated by osmotic stress, and that LvBADH is involved in the cellular response of crustaceans to variations in environmental salinity. [ABSTRACT FROM AUTHOR]