Biochemical and immunological studies on the P400 protein, a protein characteristic of the Purkinje cell from mouse and rat cerebellum.

The P400 protein is a glycoprotein of high apparent molecular weight which is abundant in isolated cerebellar Purkinje cells. On SDS polyacrylamide gels, the P400 protein reacts with 125I plant lectins such as 125I Con A. This reaction is used to increase the level of detection of the protein. The P400 protein is purified by successive extraction of synaptosomal and microsomal membranes with 2% Triton X-100 and 25% Na-cholate and preparative gel electrophoresis in SDS. The specific content of P400 protein decreases in the cerebella from homozygous nervous and Purkinje cell degeneration mutant mice, where the total number of Purkinje cells is markedly reduced, and increases in those of the reeler and weaver mice where a deficit of the granule cells exists. In the cerebellum from the homozygous staggerer mouse, a small amount of P400 protein persists. During postnatal development the specific content of P400 protein per net weight does not change up to the 12th day after birth then increases up to the 25th day when it reaches the adult level. Antisera have been raised against the purified P400 protein. They give precipitation lines by the immunodiffusion reaction of Ouchterlony against a preparation of P400 protein submitted to mild proteolytic attack. Indirect immunofluorescence performed on slices of rat cerebellum with purified anti-P400 immunoglobulin G, absorbed or not on rat cerebrum membranes, reveals that both the soma and the dendritic arborization of the Purkinje cells are labelled. The neurons from the deep cerebellar nuclei are not stained.