Abstract
Saduria entomon lactate dehydrogenase (LDH-A* 4) from thorax muscle was purified about 89 fold to specific activity 510 μmol NADH/min/mg using Cibacron Blue 3GA Agarose and Oxamate-Agarose chromatographies. The enzyme is a tetramer, with molecular weight of 140 kDa for the native enzyme and 36 kDa for the subunit. The isoelectric point was at pH 5.7. The enzyme possesses high heat stability ( T 50=71.5°C). The optimum pH for pyruvate reduction reaction was 6.5, while for lactate oxidation one, the maximum activity was at pH 9.1. The K m for pyruvate was minimal at 5°C, the average environmental temperature of the isopod. The K m values determined at 30°C and optimal pH for pyruvate reduction and lactate oxidation were 0.18 and 90.04 mM, respectively. Amino acid compositional analyses showed the strongest resemblance of the isopod isoenzyme to cod ( Gadus morhua) LDH-C 4.
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