A novel brain-specific antigen: a glycoprotein electrophoretically similar to but immunochemically different from type B nucleoside diphosphatase

A monoclonal antibody, 1D4, recognizing a novel brain-specific protein was obtained. The 1D4 antigen is regarded to be a glycoprotein because it was adsorbed on the Con A-Sepharose column used for its purification. The antiserum (polyclonal antibodies) against the 1D4 antigen was raised in a rabbit and shown to react with just the same molecules as the 1D4 monoclonal antibody did. It was used to detect the antigen in crude tissue homogenates. The molecular mass of the 1D4 antigen was estimated to be 89 kDa by immunoblotting after sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the brain homogenate. The 1D4 antigen had multiple isoelectric points, the pattern of the bands detected on isoelectric focusing gel being quite similar to that of Type B nucleoside diphosphatase of the brain. However, they are distinct, since Type B nucleoside diphosphatase was not adsorbed by anti-1D4 antigen IgG-Sepharose 4B. The 1D4 antigen could not be detected in any of the peripheral organs or tissues tested. The 1D4 antigen was rich in the cerebrum, diencephalon, and cerebellum in the brain, and its content decreased with the distance of the region from the cerebrum. The amounts of the 1D4 antigen in the cerebrum and cerebellum increased with the respective developmental maturation. These findings suggest that the 1D4 antigen contributes to some brain-specific functions of the mature brain.