Cathepsin D is an estrogen-regulated protein associated with tissue breakdown. Levels of cathepsin D have been positively correlated with recurring breast cancers of both node-negative and node-positive types. Additionally cathepsin D has been associated with amyloid formation in Alzheimer's plaques. As cathepsin D activity is increased by cigarette smoke, the enzyme may contribute to lung tissue damage in smokers. Activity: >=300 units per mg protein. One unit is defined as the amount of enzyme that digests hemoglobin-releasing peptides which are soluble in 10percent TCA. The reaction is measured by an increase of an A 280 of 1.0 per 60 minutes at 37oC . Substrate: acid denatured hemoglobin, pH 1.8 (0.2percent in reaction mixture). Buffer: 100 mM formate, pH 3.3. Prepared from tissue shown to be non reactive for HbsAG, anti-HCV, anti-HBc, and negative for anti-HIV 1 & 2 by FDA approved tests. >95percent pure by SDS-PAGE. Add deionized water to original volume, aliquot and freeze unused portion.