Glucose-6-phosphate dehydrogenase isozymes in fish--a comparative study

Area of Science:

• Biochemistry
• Comparative Physiology
• Enzymology

Background:

• Glucose-6-phosphate dehydrogenase (G6PD) is a key enzyme in carbohydrate metabolism.
• Isozymes of G6PD exhibit variations in substrate specificity and electrophoretic mobility.
• Understanding fish G6PD isozymes provides insights into evolutionary adaptations and metabolic pathways.

Purpose of the Study:

• To characterize the electrophoretic distribution and substrate specificities of G6PD isozymes in seven teleost fish species.
• To compare G6PD isozyme patterns across different fish orders (Albuliformes and Perciformes).
• To investigate the catalytic capabilities of fish G6PD isozymes with various monosaccharide phosphates.

Main Methods:

• Horizontal starch gel electrophoresis was employed to separate G6PD isozymes.
• Gel slices were stained using diverse substrates and cofactors to determine enzyme specificities.
• Substrate specificity assays included glucose-6-phosphate (G6P), galactose-6-phosphate, and fructose-6-phosphate.

Main Results:

• Seven teleost fish species were analyzed, including bonefish (Albulidae) and perciform species (Chaetodontidae, Mullidae, Gobiidae, Lutjanidae).
• Most species displayed two isozyme groups: G6PD (specific for G6P and NADP+) and H6PD (utilizing other hexose phosphates).
• A single, rapidly migrating G6P- and NADP+-specific G6PD isozyme was observed in most species, except for the goby (Gobiidae).
• All fish isozymes demonstrated significant catalytic activity with fructose-6-phosphate, comparable to G6P.
• The goby exhibited five isozymes, none of which were specific for G6P.

Conclusions:

• Fish G6PD isozymes show interspecific variation, particularly in the goby.
• The broad substrate specificity of fish G6PD, including fructose-6-phosphate, suggests a potential role beyond G6P oxidation.
• These findings imply that fish G6PD may compensate for glucosephosphate isomerase activity in monosaccharide metabolism.