Species restriction of a monoclonal antibody reacting with residues 130 to 137 in encephalitogenic myelin basic protein.

A monoclonal antibody (immunoglobulin G1) has been produced that reacts against myelin basic protein present in or extracted from the brains of many mammals-with certain important exceptions. Because of known species differences in amino acid sequences of basic protein and of certain peptide fragments, the binding site for this particular antibody appeared likely to include residues 130 to 137. Confirmation of this hypothesis was obtained by amino acid composition of the major immunoreactive peptides produced by thermolysin digestion of human basic protein and isolated by high-performance liquid chromatography.

Effect of protein concentration on the molecular weight of delta5-3-ketosteroid isomerase.

The molecular weight of delta-5-3-ketosteroid isomerase from Pseudomonas testosteroni was determined by means of sedimentation equilibrium and exclusion chromatography over a wide range of enzyme concentrations in 0.2 M potassium phosphate buffer, pH 7.0. In addition, the sedimentation constant of the enzyme was determinded over an extended range of concentrations. The enzyme was found to have a molecular weight of 26,000 plus or equal to 1,000, suggesting that it is a dimer of identical or similar 13,400 molecular weight polypeptide chains. In the ultracentrifuge this dimeric species was found to undergo aggregation at enzyme concentrations above 2 mg per ml and dissociation at enzyme concentrations below 0.05 mg per ml. Exclusion chromatography studies indicate that under the conditions of chromatography the oligomeric enzyme is partially dissociated at enzyme concentrations in the range 0.2 to 0.002 mug per ml. These results suggest that under conditions of enzyme assay in 0.2 M potassium phosphate buffer, pH 7.0, isomerase is in a monomeric state of aggregation.