Rapid spectrophotometric determination of Acholeplasma laidlawii membranes

The amount of Acholeplasma laidlawii membranes can be accurately, rapidly, and simply determined by spectrophotometric measurements after solubilization in 0.02 M SDS, 0.02 M Tris-HCl (pH 8.0). Extinction coefficients from the 260- to 300-nm-absorption region are adequate for quantitative membrane determination. The following values were found: E1%1cm,280 = 9.11 +/- 0.63, E1%,S1cm,280 = 8.52 +/- 0.40 (corrected for light scattering), E1%1cm,280--310 = 8.15 +/- 0.35. The last value is the most satisfactory for routine analysis. These coefficients are not affected by large differences in the carotene and flavin contents of the membranes or by spectral changes that occur when the membranes are exposed to light. The precision obtained with this method is comparable with that achieved in spectrophotometric determinations of proteins. As little as 6 microgram of membrane can be measured in 50-microliter samples.