Regional distribution of S-100a(0) (??), S-100a (??) and S-100b (??) in the bovine central nervous tissue determined with a sensitive enzyme immunoassay system.

A sensitive sandwich-type enzyme immunoassay system for separate measurement of 3 forms of bovine S-100 protein, S-100a(0) (??), S-100a (??) and S-100b (??), was developed by the use of purified antibodies to the ? or the ? subunit of bovine S-100 protein. The assay system consisted of polystyrene balls with immobilized antibody (anti-? for S-100a(0) and S-100a assays, and anti-? for S-100b assay) F(ab?)(2) fragments and antibody (anti-? for S-100a, assay, and anti-? for S-100a and S-100b assays) Fab? fragments labeled with ?-d-galactosidase from Escherichia coli. The minimum measurable sensitivity of each assay was less than 10 pg/assay tube. The assay system for S-100a cross-reacted little with S-100a(0) and S-100b. The assay systems for S-100a(0) and S-100b cross-reacted (10 and 17%, respectively) with S-100a which contains ? and ? subunits in the molecule. However, levels of S-100a(0), S-100a and S-100b in the soluble extract of bovine brain could be determined by correcting the cross-reacted S-100a to the assays of S-100a(0) and S-100b. Various regions of bovine central nervous tissue were found to contain 0.3-1 ?g of S-100a(0), 4-14 ?g of S-100a, and 8-30 ?g of S-100b per mg soluble protein. The percent concentrations of three forms of S-100 protein in the cerebral cortex were about 3, 38, and 59, for S-100a(0), S-100a, and S-100b, respectively, and those in the cerebellar cortex were 2, 21 and 77, respectively. Purified S-100a and S-100b preparations from human and rat brains were also reactive with the respective assay system for bovine S-100 protein, suggesting that the present assay system is applicable to the assay of three forms of S-100 protein in human and rat tissues.