Comparisons of the effects of temperature on the liver fatty acid binding proteins from hibernator and nonhibernator mammals

Hibernating mammals rely heavily on lipid metabolism to supply energy durin g hibernation. We wondered if the fatty acid binding protein from a hiberna tor responded to temperature differently than that from a nonhibernator. We found that the K-d for oleate of the liver fatty acid binding protein (1.5 mu M) isolated from ground squirrel (Spermophilus richardsonii) was temper ature insensitive over 5-37 degrees C, while the rat liver fatty acid bindi ng protein was affected with the K-d at 37 degrees C being about half (0.8 mu M) that found at lower temperatures. This same trend was observed when c omparing the specificity of various fatty acids of differing chain length a nd degree of unsaturation for the two proteins at 5 and 37 degrees C. At th e lower temperature, ground squirrel protein bound long-chain unsaturated f atty acids, particularly linoleate and linolenate, at least as well as at t he higher temperature and matched requirements for these fatty acids in the diet. The most common long-chain fatty acid, palmitate, was a more effecti ve ligand for ground squirrel liver fatty acid binding protein at 5 degrees C than at 37 degrees C, with the opposite occurring in the eutherm. Rat pr otein was clearly not adapted to function optimally at temperatures lower t han the animal's body temperature.