Properties of NADP-dependent isocitrate dehydrogenase from the mussel Mytilus edulis L.

Abstract

1.1. NADP-dependent isocitrate dehydrogenase (ICDH) activity has been measured in the digestive gland, mantle, gill, adductor muscle and foot of Mytilus edulis. The highest specific activities were found in the digestive gland and the lowest activities in the adductor muscle and the mantle tissue.2.2. ICDH was partially purified from the digestive gland and mantle tissue. The enzyme from the digestive gland was mainly cytoplasmic. The molecular weight by gel filtration was 71,000 (±7000), for both the digestive gland and mantle enzymes.3.3. ICDH was inactive in the absence of metal ion and in vitro both Mn2+ and Mg2+ were shown to be activators.4.4. The Km values for d-isocitrate, measured over a range of pH from 6.5–8.0 were found to be constant and identical in both tissues (approx 3 μm). The Km value for NADP was approx 3 μM.5.5. The Km values for d-isocitrate and maximal reaction rates were measured over a range of temperatures (5–25°C). The Km values increased with increasing temperature. Q10 values (Vmax) were approx 3 (5–15°C) and 2 (15–25°C) for both tissues.6.6. ICDH from the digestive gland of M. edulis was not inhibited by ATP or palmitoyl-CoA. It was inhibited slightly at 1 mM levels of either glyoxalate or oxaloacetate and was inhibited strongly when the two effectors were added together.