Simple estimation of the differential absorption coefficient of P-700 in detergent-treated preparations

The apparent differential absorption coefficient of P-700 in the thylakoid membranes and Photosystem I particles from the cyanobacterium Synechococcus elongatus was differently affected by various detergents. Triton X-100 and sodium dodecyl sulfate increased the differential absorption coefficient, whereas the absorption value was reduced by digitonin and octyl-d-glucoside. Irrespective of detergents used, however, variations of the differential absorption coefficient were well related to band shifts of chlorophyll a molecules at 690 nm. The band shift also affected, in opposite directions, the two bleaching bands at 680 nm and 700 nm of the P-700 difference spectrum. Thus the differential absorption coefficient of P-700 in detergent-treated preparations can be estimated by measuring the ratio of the 680 nm to 700 nm bands.