Purification and characterisation of octopine dehydrogenase from the marine nemerteanCerebratulus lacteus(Anopla: Heteronemerta): comparison with scallop octopine dehydrogenase
✍ Scribed by G. Gäde; K. -H. Carlsson
- Book ID
- 104759717
- Publisher
- Springer-Verlag
- Year
- 1984
- Tongue
- English
- Weight
- 864 KB
- Volume
- 79
- Category
- Article
- ISSN
- 0025-3162
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✦ Synopsis
Octopine dehydrogenase from the nemertean Cerebratulus lacWus was purified over 1 000-fold to almost homogeneity. The enzyme does not bind to arginine Sepharose 4B. It has a monomeric structure with a relative molecular mass of 40 000. Two isoenzymes were identified with isoelectric points of 5.6 and 5.4, whereas the purified isoenzymes of Pecten jacobaeus adductor muscle (which bind to arginine Sepharose 4B) had lower IEP's of 4.9 and 4.7. Apparent Km's of the nemertean ODH for arginine and pyruvate are dependent on the respective co-substrate concentration. This phenomenon may result in activation of ODH and, thus, production of octopine in locomotory highly active individuals while attacking food, especially when this takes place in a hypoxic habitat, such as decaying mud near the high-water mark. The apparent Km's for octopine (0.22 mM) and NAD + (14#M) are low. Octopine is a substrate inhibitor for the reverse reaction above 2 mM, and a product inhibitor of the forward reaction by 50% at 1.2 mM. Therefore, only small amounts of octopine are likely to accumulate in vivo. Amino acid substrate specificity is limited to guanidino amino acids. We believe that the amino acid substrate specificity is not an evolutionary modification, but rather that it is narrowed to guanidino amino acids (or even specificity to arginine) in those species where ODH has a physiological function in maintaining redox balance during exercise. The specificity for keto acids is dependent on chain length, (a-ketobutyrate>a-ketocapronate); a second carboxyl group inactivates the enzyme.