Automated determination of protein in the presence of sucrose

The advent of the zonal centrifuges utilizing sucrose density gradients has made it necessary to measure routinely the protein content of subcellular fractions containing variable amounts of sucrose with automated procedures. The color development in the Lowry reaction was found to be progressively reduced by increasing concentrations of sucrose. The sucrose inhibition could be overcome by increasing the amount of copper in the system. However, the copper-tartrate reagent was extremely unstable, and the copper quickly precipitated out. The copper-tartrate was stable when dissolved in bicarbonate buffer, but this modification failed to overcome the sucrose effect. Sucrose failed to impair the contribution of the Folin reaction to color development, and sufficient sensitivity could be obtained by using the new Technicon tubular flow cell with a 15 mm light path. Under these conditions a linear response to protein concentration was obtained from 0.05 to 8.00 mg bovine serum albumin per millititer.