Inhibitors of Photosynthetic Electron Transport. The Properties of Diazidodialkylbenzoquinones

The potential photoaffinity reagents 2,5-diazido-3-methyl6-isopropyl-l,4-benzoquinone (DAZMIB) and 2,5-diazido-3,6dimethyl-l,4-benzoquinone (DAZDMQ), which are analogs of the well-known inhibitor 2,5-dibromo-3-methyl-6-isopropyl1,4-benzoquinone (DBMIB), block photosynthetic electron transport in spinach chloroplasts. On irradiation, at relatively high concentrations, DAZMlB inhibits electron flow irrevers­ ibly. However, when [3H] DAZDMQ was photolyzed with chloroplasts, no labeling of the membrane proteins was ob­ served. Rearrangements of the nitrenes derived from the oxidized or reduced azidoquinones that might account for this behaviour are discussed.