Effects of temperature on the kinetics of malate dehydrogenases in the developing eggs and adult muscle ofAscaris lumbricoides (Nematoda)
✍ Scribed by Barrett, John ;Fairbairn, Donald
- Publisher
- John Wiley and Sons
- Year
- 1971
- Tongue
- English
- Weight
- 622 KB
- Volume
- 176
- Category
- Article
- ISSN
- 0022-104X
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✦ Synopsis
The effects of temperature on the kinetics of the different cytoplasmic malate dehydrogenases which are present during the life cycle of Ascaris lumbricoides were studied. Aerobic development of the eggs occurs below 32"C, whereas anaerobic energy metabolism in adults occurs at 38-40°C. Eggs developed for one day have one cytoplasmic MDH (MDH-l), fully developed infective 21-day eggs have 3 dehydrogenases (MDH-I, 2 , 3 ) and adult muscle has the same three isozymes but in proportions favoring MDH-2 and 3. Values for V,,,,,,, energy of activation, and the thermal stability of the total enzyme or of individual isozymes were not clearly correlated with temperature changes occurring during the life cycle. In contrast, the apparent Michaelis constants (Km,) were directly correlated. The Km., of MDH-1 and MDH-3 passed through minima at 25°C and 38"C, respectively; the Km, of MDH-2 showed no clear minimum. The distribution of the isozymes during development was such that the Km, of total malate dehydrogenase at one day, 2 1 days, and in adult muscle was minimal at 25"C, 30"C, and 38"C, respectively. The results are considered in terms of epigenetic adaptation, i.e., malate dehydrogenase in one-day eggs and adult muscle is adapted to function efficiently at temperatures normal to those stages, whereas infective eggs also possess large amounts of isozymes which are probably only functional during the succeeding stages of development.