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Journal of Comparative Physiology B

, Volume 158, Issue 4, pp 487–493 | Cite as

pH-temperature interactions on protein function and hibernation: GDP binding to brown adipose tissue mitochondria

  • A. Malan
  • E. Mioskowski
Article

Summary

  1. 1.

    [3H]GDP binding to the uncoupling protein of brown adipose tissue was determined on mitochondria isolated from hibernating European hamsters, at two temperatures, 35 and 15°C, and four values of25pH (pH corrected to 25°C): 6.4, 6.8, 7.2 and 7.6, encompassing the physiological range of pH. Buffer composition was adjusted to get the same pH-temperature relationship as for mammalian blood, in which this relationship is mainly determined by protein imidazole buffers.

     
  2. 2.

    The maximal binding capacity was independent both of temperature and pH. The dissociation constantKD was highly pH-dependent, but was independent of temperature when25pH was held constant. Under these conditions, the uncoupling protein thus fully conserves its regulatory properties over the temperature range studied (eurythermal adaptation).

     
  3. 3.

    The temperature coefficient of the apparent pK′ for the pH effect (−0.012±0.004) differed significantly from that of GDP terminal phosphoryl group, but not from that of blood protein imidazole buffer groups, in good agreement with the imidazole alphastat theory.

     
  4. 4.

    The results indicate that GDP reaction with the protein involves an electrostatic binding with a titratable group of the protein, probably a sulfhydryl.

     
  5. 5.

    pH modulation of the uncoupling of brown adipose tissue mitochondria probably permits a reversible control of thermogenesis in the hibernation cycle, heat dissipation being inhibited by respiratory acidosis in deep hibernation, but facilitated by the hyperventilation of arousal.

     

Keywords

Sulfhydryl Brown Adipose Tissue Phosphoryl Uncouple Protein Respiratory Acidosis 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Abbreviations

α1m

dissociation ratio of protein imidazole groups

Bmax

maximal binding capacity

dpH/dT

temperature coefficient of pH

dpK′/dT

temperature coefficient of the apparent ionization constant

EDTA

ethylene diamine tetraacetic acid

GDP

guanosine diphosphate

KD

dissociation constant, here for GDP

25pH

pH determined after bringing the sample to 25°C in closed-system conditions (Malan 1977)

pKD

log(KD)

Tb

body temperature

TES

N-tris(hydroxymethyl) methyl-2-aminoethane sulfonate

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Copyright information

© Springer-Verlag 1988

Authors and Affiliations

  • A. Malan
    • 1
  • E. Mioskowski
    • 1
  1. 1.Laboratoire d'Etude des Régulations Physiologiques (associated with Université Louis Pasteur)CNRSStrasbourgFrance

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