Improvement in separation of system I and system II particles of photosynthesis obtained by digitonin treatment

By a combined use of digitonin treatment and subsequent centrifugation on a linear sucrose density gradient, the whole green material of the chloroplast lamellae was separated into System I and System II particle fractions, leaving no other fractions of intermediate properties at the final step of separation.

Each of these particle fractions obtained had properties characteristic of System I or System II with respect to the molar ratio of chlorophyll a/chlorophyll b, the content of P700, the fluorescence emission spectrum at −196°;, photoreduction activities with ferricyanide and NADP⁺, and induction of fluorescence.

About 40 and 50% of the total chlorophyll in the original chloroplasts were recovered in System I and System II particles, respectively. Only small amounts of total chlorophyll (less than 10%) were found as free chlorophyll detached from the lamellae through the digitonin treatment.

These results support the view that the lamellae of chloroplasts are composed of about equal amounts of System I and System II particles on a chlorophyll basis.