Pyruvate‐sensitive AOX exists as a non‐covalently associated dimer in the homeothermic spadix of the skunk cabbage, Symplocarpus renifolius
Yoshihiko OndaYoshiaki KatoYukie AbeTakanori ItoYasuko Ito‐InabaM. MorohashiYuka ItoMegumi IchikawaKazushige MatsukawaMinoru OtsukaHiroyuki KoiwaKikukatsu Ito
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Abstract:
The cyanide‐resistant alternative oxidase (AOX) is a homodimeric protein whose activity can be regulated by the oxidation/reduction state and by α‐keto acids. To further clarify the role of AOX in the skunk cabbage, Symplocarpus renifolius , we have performed expression and functional analyses of the encoding gene. Among the various tissues in the skunk cabbage, SrAOX transcripts were found to be specifically expressed in the thermogenic spadix. Moreover, our data demonstrate that the SrAOX protein exists as a non‐covalently associated dimer in the thermogenic spadix, and is more sensitive to pyruvate than to other carboxylic acids. Our results suggest that the pyruvate‐mediated modification of SrAOX activity plays a significant role in thermoregulation in the skunk cabbage.Keywords:
Homeothermy
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SummaryWe compared the degree of homeothermy, the level of peak metabolic rate, and minimal thermal conductance in shorebird neonates of 15 species (neonatal body mass 4–55 g) with literature data on duck neonates of 11 species (neonatal body mass 17–61 g). In addition, we have studied the development of homeothermy in shorebird chicks during postnatal growth. In shorebird neonates a positive relationship existed between neonatal body mass and degree of homeothermy. In contrast, duck neonates of all sizes appeared to be homeothermic. The observed differences in degree of homeothermy between shorebird and duck chicks could almost entirely be explained by differences in peak metabolic rate.
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Abstract The dispersion of heat is driven by the universe’s thermodynamic imperative, against which rage the furnaces of animal homeothermy. Body heat offers the scythe of speed to animals of advanced phylogeny. In the current animal kingdom, however, only birds and mammals are able to maintain a body temperature that is substantially warmer than their surroundings. Lower animals are cold-blooded, or poikilothermic, which means internal body temperature fluctuates with ambient temperature. Warm-blooded animals are homeothermic because they maintain a constant internal body temperature (core temperature) that is higher than the average temperature of the environment in which they live. This characteristic, which in cooler climates has a strong survival advantage, results from the ability to conserve the metabolic heat every cell in the body generates during the process of homeostasis.
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