SUBCELLULAR-DISTRIBUTION OF ADENYLYL CYCLASE AND GS-ALPHA IN RAT BROWN ADIPOSE-TISSUE

The subcellular distribution of Gsα (the α-subunit of guanine nucleotide-binding stimulatory protein of adenylyl cyclase) was examined in interscapular brown adipose tissue (IBAT) to determine (1) if Gsα is completely colocalized with adenylyl cyclase in the plasma membrane, and (2) whether cold exposure, which increases adenylyl cyclase activity, changes the subcellular distribution of Gsα. Subcellular fractions were prepared from IBAT by differential centrifugation and analyzed for Gsα by immunoblotting. Adenylyl cyclase activity and Gsα were detected in all the subcellular fractions except the cytosol. The plasma membrane fraction showed the greatest enrichment of adenylyl cyclase and Gsα. However, the enrichment of adenylyl cyclase in the plasma membrane fraction was greater than that for Gsα, which was also associated to a large degree with the mitochondrial fraction. Thus, compared with the mitochondrial fraction, both 5′ nucleotidase and adenylyl cyclase were enriched by over 200% in the plasma membrane fraction, but Gsα was enriched by only 50%. Exposure of rats to 4°C for 3 days increased fluoride-stimulated adenylyl cyclase activity, but did not increase the amount of immunoreactive Gsα in any of the subcellular fractions examined. The above results demonstrate that not all Gsα in IBAT is colocalized with adenylyl cyclase in the plasma membrane. The finding that cold exposure did not change the subcellular distribution of Gsα indicates that the cold-induced increase in adenylyl cyclase activity is not due to translocation of Gsα from subcellular compartments to the plasma membrane. © 1991.