Cat allergen 1: Biochemical, antigenic, and allergenic properties

Cat allergen 1, an important agent in human allergic reactions, has been partially purified by affinity chromatography. Heating the purified allergen at 100 degrees C for 30 min resulted in a 28% loss in the antigenicity of the allergen molecule (determined by Laurell rocket assay), although lower temperatures had little effect. Its allergenicity (determined by passive transfer skin test) was diminished slightly after heating to 56 degrees C or 100 degrees C. Reduction with dithiothreitol or 2-mercaptoethanol resulted in greater losses of antigenicity and allergenicity but did not obliterate these properties. Three forms of the affinity-purified allergen (isoallergens) differing slightly in isoelectric point were demonstrated by isoelectric focusing followed by crossed immunoelectrophoresis. The molecular weight of cat allergen 1 under physiologic conditions was 35,000 +/- 2000 as determined by gel filtration in Sephadex G-75. Under the dissociative conditions of sodium dodecyl sulfate-polyacrylamide gel electrophoresis, with or without prior reduction by dithiothreitol, cat allergen 1 appeared to exist as an antigenically active subunit with a molecular weight of 18,000 +/- 2000. This subunit molecular weight estimate was confirmed by gel filtration in 6M guanidine hydrochloride. The stability of the allergenic and antigenic activity of cat allergen 1 suggests that this activity may be determined partially by the primary sequence of allergenic sites on the molecule. The separation and purification of molecular subunits may allow sequence analysis of these sites.