A micromethod for the quantitation of cellular proteins in Percoll with the Coomassie brilliant blue dye-binding assay

A simple procedure for the determination of cellular proteins in Percoll-containing samples is described. Percoll precipitated when particulate proteins were solubilized by dilution of the samples in a NaOH-Triton X-100 mixture. After centrifugation at high speed (12,000g), the supernatant was assayed for proteins with the Coomassie brilliant blue dye-binding assay. With an automatic spectrophotometer, 50-microliter aliquots gave a linear response between 0 and 3 micrograms of bovine serum albumin. After a fivefold dilution in the alkali-detergent mixture, proteins in samples containing up to at least 60% Percoll can be accurately quantitated on a standard curve prepared in the absence of Percoll. Because the sensitivity of the assay was better than 100 ng, the procedure outlined in this paper can also be used as a general protein micromethod.