Effects of Hydroxylamine on Photosystem II: I. Factors Affecting the Decay of O(2) Evolution.

Illumination of chloroplasts in the presence of NH(2)OH (2 mm) leads to the destruction of all system II activities without affecting system I activity. The system II primary charge separation remains intact when incubated with this agent in the dark with release of one of the system II Mn pools and simultaneous destruction of O(2) evolving capacity. The size of the Mn pool associated with the O(2) evolving center is calculated to be 4 Mn/O(2)-evolving center.We observed the following properties of the hydroxylamine-induced destruction of O(2) centers in darkness: [List: see text]Chloroplasts from summer greenhouse spinach (4-5 Mn/400 chl(total) or 50 to 60% of the Mn pool of the O(2)-evolving center) showed high quantum requirement for O(2) evolution (5-6 hv/equivalent) yet photooxidized NH(2)OH with low quantum requirement ( approximately 2 hv/equivalent).