Stable Lowry Protein Assay Kit: The Lowry procedure involves reaction of protein with cupric sulfate and tartrate in an alkaline solution, resulting in the formation of tetradentate copper-protein complexes. When the Folin-Phenol Reagent is added, it is effectively reduced in proportion to these chelated copper complexes,producing a water-soluble product whose blue color can be measured at 750 nm. For the original Lowry method, the alkaline copper-tartrate reagent (Reagent C) must be prepared fresh daily from two other reagents (Reagents A and B). For this assay we have developed a modified cupric sulfatetartrate reagent that replaces individual Reagents A and B of the original Lowry method with a single stable reagent that substitutes for Reagent C. The color response curves for the Stable Lowry Protein Assay and the original Lowry method have nearly 100% correlation. Accordingly, the Stable Lowry Protein Assay Kit is ideal for loyal Lowry method users who would like the increased convenience of a stable, pre-formulated product. As with other protein assay procedures, the Stable Lowry Protein Assay produces slightly different color response curves for different proteins and can be affected by certain components in the sample buffer. Accordingly, protein concentrations generally are determined and reported with reference to standards of a common protein such as bovine serum albumin (BSA), which is included in this kit. A series of dilutions of known concentration are prepared for plotting BSA standard curve, and then the concentration of each unknown is determined based on the standard curve. The linear range of this assay is 5-100μg/ml. This kit is sufficient for 1000 microplate assays or 100 test tube assays.