Concentration of rat brown adipose tissue uncoupling protein may not be correlated with 3H-GDP binding

Rats fed diets low in protein or exposed to cold show an increase in brown adipose tissue (BAT) mitochondrial 3H-GDP binding. To investigate this phenomenon further, the uncoupling protein associated with BAT function was measured immunochemically on nitrocellulose blots. Quantitation of uncoupling protein was achieved by densitometer scanning with a BioRad densitometer. Peaks were integrated with Chromatochart software and an Apple IIe computer. A standard curve of purified uncoupling protein (50 to 500 ng) was used to calculate uncoupling protein concentration. There is a 1.5-fold increase in uncoupling protein per mg of protein in BAT mitochondria from rats exposed to cold for 15 days. There was no decrease in uncoupling protein from rats exposed to the cold followed by 24 h at 270C although 3H-GDP binding had decreased by half. Rats fed diets containing either 5 or 15% lactalbumin for 3 weeks did not show differences in uncoupling protein concentration although 3H-GDP binding was 1.5-fold greater in BAT mitochondria from the low protein group. These results indicate that GDP binding does not necessarily reflect the concentration of uncoupling protein in BAT mitochondria