Quantitation of natural rubber latex proteins: Evaluation of various protein measurement methods

The allergy to natural rubber latex (NRL) proteins is a significant occupat ional health hazard. The elimination or reduction of the water-soluble prot eins from finished NRL products is one approach aimed at decreasing further sensitization and reactions to these allergens. To achieve this goal, a re liable protein measurement method is required. Several published and widely used methods for protein measurement in finished NRL products demonstrate major inconsistencies in the quantification of extractable NRL proteins in, comparison to the Kjeldahl nitrogen assay and the gravimetrically determin ed reference. Multiple protein assays and several reference proteins were e xamined to determine the most suitable method for the quantitation of solub le NRL proteins. Among the reference proteins evaluated (BSA, BGG, and OA), OA was found to correlate best with gravimetrically determined levels of N RL proteins. Of the protein assays evaluated (Bradford, BCA, and Lowry), th e modified Lowry assay demonstrated the best uniformity and a good correlat ion with the Kjeldahl nitrogen assay. The commercial Lowry assay kit, Bio-R ad DC Protein Assay, was comparable to the laboratory-prepared reagents, an d both demonstrated good sensitivity and precision. Altering a sample to re agent ratio increased the sensitivity of the test.