| Summary: | The present study is concerned mainly with partial purification and
characterization of cytosolic GST from livers of Malaysian catfish and Malaysian
red tilapia as both species are of economic and commercial importance in
Malaysia being the major freshwater fishes consumed. This study hopes to
establish the patterns of cytosolic glutathione S-transferase isoenzymes in the
catfish and red tilapia. This may be useful to further achieve an understanding
toward this enzyme in view of using it as a tool in environmental monitoring. The
hepatic GST enzyme from catfish and red tilapia was partially purified 15X and
27X respectively in comparison to the ultra-centrifuged cytosolic fraction by
affinity chromatography. Specific GST activity of 12.69 unitlmg protein and 33.42
unitlmg protein was obtained from livers of catfish and red tilapia using l-chloro-
2,4-dinitrobenzene (CDNB) as a substrate. Isolation of GST isoenzymes from
affinity purified fractions was achieved by preparative isoelectric-focusing. Two
isoenzymes; one major isoenzyme designated Cil and one minor isoenzyme
designated Ci2 were isolated from catfish liver with an apparent pl of 6.20 and
8.73 respectively. One isoenzyme designated Ti1 was isolated from red tilapia
liver with an apparent pi of 9.14. SDS-PAGE analysis suggests that the isolated
isoenzymes appear to be homodimeric in nature with subunit molecular weight
of 29.7 21.7 kDa (Cil), 27.7 21.3 kDa (Ci2) and 29.9 +0.9 kDa (Til). As has
been found for most GSTs, highest catalytic activity was obtained with CDNB.
With the exception of the isoenzyme from cytosol and affinity purified fractions of
red tilapia, none of the catfish fractions displayed enzyme activities towards 1,2-
dichloro-4-nitrobenzene (DCNB) and ethacrynic acid (EA). Therefore, both
catfish and tilapia possess hepatic glutathione S-transferase activity, indicating
that they are capable of conjugating endogenous or xenobiotic
metabolites/compounds as a result of foreign exposure or oxidative metabolism
with glutathione, thereby making it a useful tool as a effective biomarker of
aquatic contamination.
|
|---|