Identification in rat liver and serum of water-soluble class I MHC molecules possibly homologous to the murine Q10 gene product.

Abstract

We have identified large quantities of a water-soluble, non-RT1.A class I MHC molecule in the serum of the DA rat strain, with a similar molecule being found in aqueous extracts of DA liver. The non-RT1.A class I molecule have heavy chains of 41 kD, which is smaller than RT1.A class I molecules isolated from liver membrane (45 kD) but larger than water-soluble RT1.A class I molecules previously identified in serum and aqueous extracts of liver and kidney (40 kD). NH3-terminal amino acid sequencing of bulk-purified RT1.A class I molecules and of this novel non-RT1.A cells I molecules revealed two substitutions, in the first 25 amino acids. Tyr .fwdarw. His at position 9, and Ala .fwdarw. are at position 24. The non-RT1.A class I molecule did not react with any of the well-characterized polymorphic and monomorphic antibodies directed against RT1.Aa class I molecules, but did react with the MRC OX18 antibody. A similar class I molecule could not be defined on liver menbranes. The non-RT1.A class I molecule was found in large quantities (.apprx. 20 .mu.g/ml) in the serum of the DA rat strain, and similarly large quantities appear to be present in the sera of BN, PVG, and LEW.RT1a rats. WAG and LEW.RT1u rats had readily detectable but lower amounts of this molecule in their serum, while LEW and SHR rat had little if any present. This muscle probably represents the rat homologous of the murine Q10 gene product, and is the major class I produced in the serum of the DA rat strain.