Glutathione transferase (GST) and glutathione reductase (GR) are two enzymes that play important roles in cellular antioxidant defense and redox regulation. The concentration of these enzymes can be calculated from their optical density (OD) values, which measure the amount of light absorbed by a sample at a specific wavelength. Here is a general method to calculate the concentration of GST and GR:

where pathlength is the thickness of the cuvette or the distance that light travels through the sample.

Note: These calculations assume that the enzymatic activity of the GST and GR samples is proportional to their concentration and that the OD values are proportional to the activity. It's also important to use the correct wavelength for each enzyme, as different enzymes may have different extinction coefficients at different wavelengths.