Optimization of the lowry method of protein precipitation from theH. influenzae type b conjugate vaccine using deoxycholic acid and hydrochloric acid

The Lowry method was used in this study to measure protein inHaemophilus influenzae type b (Hib) conjugate vaccines (polyribosylibitol phosphate-tetanus toxoid; PRP-TT) using deoxycholic acid (DOC) to induce protein precipitation. Trichloroacetic acid (TCA) did not induce precipitation adequately from the Hib conjugate bulk and the freeze-dried Hib conjugate product. Its yield was approximately 50%. The matrix structure of Hib conjugate inhibits precipitation by TCA. Although the Lowry method can be carried out without precipitation in Hib conjugate bulk when no residual impurities (adipic acid dihydrazide [ADH], 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide-HCI [EDAC], phenol and cyanogens bromide [CNBr],etc.) are present, it cannot be used for Hib conjugate products that contain sucrose 8.5%, because 8.5% concentration of sucrose enhanced the protein concentration. DOC- and HCI-induced precipitation is an alternative method for evaluating the protein content of the Hib conjugate bulk and the Hib conjugate product. The precipitation was optimal with a final concentrate of 0.1% for DOC at 4°C and pH 2. This Lowry method, using DOC/HCI precipitation to induce protein precipitation, was confirmed a consistent, reproducible, and valid test for proteins in Hib conjugate bulk and its freeze-dried product.