Purification and properties of a carboxylesterase from the liver of tiger shark (Galeocerdo cuvier)

Abstract

A procedure is described for the purification of a carboxylesterase from shark liver, using a chloroform-acetone powder prepared from the liver as the starting material. The yield of purified enzyme is approximately 50 mg from 530 g of chloroform-acetone powder. The preparation is electrophoretically homogeneous. Active-site titrations with paraoxon gave an equivalent weight of approximately 83 000. The molecular weight, found from sedimentation equilibrium experiments, is approximately 80 000. There is no evidence of any association or dissociation of this species. The enzyme shows a marked preference for aryl esters over alkyl esters, in contrast to other carboxylesterases so far studied. The amino acid composition of the purified enzyme is reported.

Determining the appropriate pretreatment procedures and the utility of liver tissue for bulk stable isotope (δ13C and δ15N) studies in sharks

“…( ) LE; ( ) LEWW tissue-specific, related to amino acid composition (McMahon et al, 2010(McMahon et al, , 2015) and therefore we suggest that elasmobranch liver tissue may be delipidated at C:N ratios of 4.0. Examination of tiger shark (Galecocerdo cuvier) liver tissue amino acid composition (Scott et al, 1976) resulted in an overall C:N value of 4.1, confirming that the C:N ratio of fully delipidated elasmobranch liver is above the universally accepted delipidated muscle C:N ratio of 3.5. Through examining the relationship between δ 13 C and C:N for each shark species and accepting some lipid bias still present in liver samples, our "C:N threshold" approach provides a conservative method to derive ecologically viable species-specific C:N values for each treatment type (i.e., LE vs.…”