Molecular mechanisms of adaptation to low temperature in marine poikilotherms. Some regulatory properties of dehydrogenases from two arctic species
✍ Scribed by H. W. Behrisch
- Publisher
- Springer-Verlag
- Year
- 1972
- Tongue
- English
- Weight
- 768 KB
- Volume
- 13
- Category
- Article
- ISSN
- 0025-3162
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✦ Synopsis
The properties of gluooso-6-phosplmto dehydrogenase and 6-phogphoglueonate dehydrogomme from gill tissue of the farmer crab Chionoce~ bairdi, and lactate dehydrogonaso (LDtt) and glyeeraldehydo dehydrogenaso from skeletal musole of U. ba/rdi and the yollowfin sole/Amanda aspera were examined over the physiological temperature range of the anlmt~18. ]~t~h a, nimMa wero obtained in the Bering See, in winter, and their enzymes appear to be remarkably ooldadapted. Affinity of sole LDH for substa'ate appears to in. oroase with decreasing temperature, thus keeping reaction rate cesentiaUy independent of temperature at physiologioal concentrations of the sub.rate. Calculat~l values of activation energy are low, in keeping with the argument that organisms from cold environments have enzyme~ with a reduced energy of activation-In addition, Htr.r, plots of the substrato ssmration curves for lactate dehydrogenaso from mnsole of sole indicate that there is a faoilitation of allosterio behaviour &t; low temlxu-'aturos. Maximum ~fRnlty of sole LDH for substrate in the absence of univalent cations ooours at 3 ~ while in the presence of 150 mNK +, it occurs bo~woen 0 ~ to --2 ~ The effects of Mg s+ on enzyme aetivity appear to be determined by concentwation of substrate and temperature. Thus, glueeso-6-phosphate dahydrogenase and ~phesphoglucenate dehydrogenase am stimulated more effectively by Mg ~+ at low temperature and at low substrate levels whereas, a~ high concenta-ations of substrate, they am relatively independent of the bivalent oatiom All four dehydmgenases are aff~t~cl by the univalent cations I~a+, K + and NH+~ in a maturer whioh appears to he demrmin~d, in part at least, by concentration of substrate and by temperature. These findings sugg~ meehanimna for the maintenauee and regulation of enzyme activity in poikilothermie tissues at low and changing temperatm~s.