Soluble Corticosterone-Binding Macromolecules Extracted from Rat Brain

Abstract

Soluble macromolecules which bind 3H-corticosterone both in vivo and in vitro have been extracted from the brains of adrenalectomized rats. Enzyme digestion experiments indicate that these macromolecules are proteins. Thinlayer chromatography of bound radioactivity indicates that almost 90% is unchanged corticosterone. Brain corticosterone binding protein can be distinguished from the serum corticosterone binding protein by several important properties: 1) The brain protein is present after perfusion with a Dextran-saline solution. 2) It is precipitated by protamine sulfate under conditions in which very little of the serum binding protein is precipitated, even when serum and brain extracts are mixed. 3) It migrates differently from the serum binding protein in glycerol density gradients and can be separated completely from serum binding protein on polyacrylamide gels containing glycerol. 4) Brain cytosol binding protein exchanges bound 3H-corticosterone for unlabeled corticosterone in the medium much more slowly than does the serum binding protein. Radioactive corticosterone is also bound to cell nuclei isolated from the brain, and this bound material exchanges with unlabeled corticosterone in the medium much more slowly than either the brain soluble binding protein or the serum. Both the soluble and the cell nuclear proteins which bind corticosterone have a distinctive regional distribution in the brain; they are concentrated particularly in the hippocampus and are also present in amygdala and hypothalamus as well as in other parts of the perfused rat brain. (Endocrinology90: 217, 1972)