Sedimentation behavior of fructose 1.6-bisphosphatase in crude tissue extracts of the rabbit and the rat

Abstract

The catalytically active unit of fructose 1.6-bisphosphatase from different tissue of the rabbit and the rat was determined using the “Active Enzyme Centrifugation” technique. Purified fructose 1.6-bisphosphatase from rabbit liver and muscle yielded sedimentation coefficients ( S 20, w ) between 7.20–7.46 S at room temperature. At 37 °C, sedimentation coefficients ( S 20, w ) of 7.41 and 7.36 S for fructose 1.6-bisphosphatase from liver and muscle, respectively, were obtained. The presence of either magnesium or maganese ions for the activation of the enzyme had no influence on the sedimentation rate. The addition of activators (oleate, histidine, ammonium, or potassium ions) or inhibitors (AMP or lithium ions) which affected the catalytic activity of fructose 1.6-bisphosphatase did not cause a marked change in the sedimentation coefficient. In crude tissue extracts (liver, kidney, or muscle) of the rabbit and the rat fructose 1.6-bisphosphatase activity sedimented at a rate between 7.2–7.52 S. On comparison, the observed sedimentation value of fructose 1.6-bisphosphatase activity from crude tissue extracts of the rabbit was in close agreement with sedimentation rates of purified enzyme preparations. The tetrameric form of fructose 1.6-bisphosphatase seems to be the catalytically active unit in the cytosol. Smaller or larger units possessing fructose 1.6-bisphosphatase activity have not been observed. There is no indication for interactions of fructose 1.6-bisphosphatase with other macromolecules or in particular protein-protein interactions in the cytosol.