The use of UV/visible spectrophotometers is widespread in protein analysis. The Ultrospec™
spectrophotometer series from GE Healthcare, for example, provides modules for protein
determination, enzyme activity kinetics, DNA and RNA quantitation and fraction analysis. These
units are compatible with the traditional protein determination methods described above. The
instruments are equipped with an eight-position sample changer and are optimal for protein
concentration determination with the 2-D Quant Kit.
In addition, the Novaspec™ Plus visible spectrophotometer has stored methods for protein
concentration determination by Bradford dye assay, BCA, Biuret, and Lowry assays, as well as
basic modes of absorbance, transmittance, OD600, and concentration.
2-D Quant Kit, despite its name, can be used in many different applications including
the accurate determination of protein concentration in samples. The procedure works by
quantitatively precipitating proteins while leaving interfering substances behind. The assay
is based on the specific binding of cupric ions to the polypeptide backbone of any protein
present. Precipitated proteins are resuspended in a copper-containing solution and unbound
copper is measured with a colorimetric agent. The absorbance at 480 nm is inversely related
to the protein concentration. The assay has a linear response to protein concentrations in the
range of 0 to 50 μg/ml, using a recommended sample volume of 1 to 50 μl. In addition, 2-D
Quant Kit is compatible with most reagents employed in the many techniques described for
sample preparation, such as SDS.