Tissue specific isozymes of alanopine dehydrogenase in the channeled whelk Busycotypus canaliculatum

Abstract

The tissues of the channeled whelk Busycotypus canaliculatum displayed activities of three glycolytic dehydrogenases, alanopine dehydrogenase (ADH), octopine dehydrogenase (ODH), and lactate dehydrogenase (LDH). ADH and ODH were present in all seven tissues (hepatopancreas, gill, kidney, and mantle, ventricle, foot, and proboscis muscles) tested. ADH was the major cytosolic dehydrogenase activity in all tissues except proboscis, while ODH was present in high activities only in the four muscular tissues. Significant LDH activity occurred only in the two muscles which perform sustained work, ventricle, and proboscis.Tissue specific isozymes of ADH were identified. Three forms, specific for hepatopancreas, gill–kidney, and muscle tissues, were separable by isoelectrofocusing (pI's 5.69, 5.58, and 5.93, respectively), chromatofocusing, and polyacrylamide gel electrophoresis. The three isozymes differed kinetically showing significant differences in apparent K_m^'s for L-alanine (e.g., 8.84 ± 0.03, 10.64 ± 0.40, and 13.12 ± 0.65 mM for hepatopancreas, ventricle, and gill, respectively) and even greater differences in apparent K_m's for glycine (619 ± 55, 1412 ± 115, and 2542 ± 230 mM for the above three tissues, respectively). The ratios K_m(gly)/K_m(ala) averaged 70, 192, and 132 for the three isozymes, hepatopancreas, gill–kidney and muscle, respectively.The physiological functions of ADH isozymes in the whelk may be similar to those of the M and H isozymes of LDH in vertebrates or the muscle and brain specific isozymes of ODH in cephalopod molluscs.