On the relation between size and photochemical activity of fragments of spinach grana

1. 1. The relation between the size of fragments of disintegrated spinach grana and their photochemical activity in the reaction was investigated. 2. 2. Reduction of the fragment size below 106 A3 caused a pronounced decrease of the photochemical activity. Particles of this “critical” volume presumably contain 40 to 120 chlorophyll molecules. 3. 3. The inactivation of these particles by reduction of their volume proceeds gradually. 4. 4. It was argued that the conception of the photosynthetiic unit seems to be inopportune at the present; the evidence obtained up to now only indicates the occurrence of a rate limiting enzyme in a quantity small compared with that of the chlorophyll. 5. 5. The data presented seem to indicate that the process in which this enzyme is involved in photosynthesis is linked to a one-quantum reaction