Protistology 2 (1) 54–62 (2001)
Activity and thermoresistance of some Amoeba proteus enzymes with special reference to thermal
adaptation of the amoebae
Yulia I. Podlipaeva and Alexander L. Yudin
Laboratory of Cytology of Unicellular Organisms, Institute of Cytology, Russian Academy of Sciences,
St. Petersburg, Russia Summary
Activity and thermoresistance of the Amoeba proteus enzymes - thermostable water-soluble esterases and thermolabile
water-soluble glucose-6-phosphatedehydrogenase (G6PDH) - were studied in two amoebae strains (clones) which differed in their optimal
temperature of multiplication (thermophility). In one of the clones, these characters were followed during its acclimation to relatively low
temperature 10°C within the temperature tolerant range of the clone. It was shown that specific activity and thermoresistance of both enzymes
could be regarded as strain-specific characteristics. Positive correlation between the thermoresistance of both enzymes and the thermophility
of the amoeba clone was demonstrated, representing an example of genetic temperature adaptation at the intraspecific level. No changes in
thermoresistance of esterases of the two clones were revealed during the "cold" amoeba acclimation, whereas the activity and
thermoresistance of G6PDH in cold-acclimated amoebae was increased. Electrophoretic spectra of G6PDH were identical in both amoebae
clones and at both temperatures studied. Minor fractions of the enzyme seemed to be more thermoresistant than the major one. The higher
level of G6PDH activity is presumed to be connected with activation of the antioxidant protective system. The increase of G6PDH
thermoresistance at lower temperature supports the suggestion that any temperature which disturbs the metabolic homeostasis of the
organism, may result in changes of enzyme thermoresistance which do not necessarily coincide with the same direction as the temperature
changes.
Key words: amoeba, Amoeba proteus, thermoresistance, esterases, glucose-6-phosphate dehydrogenase
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