Determination of the amount and the type of quinones present in single crystals from reaction center protein from the photosynthetic bacterium Rhodopseudomonas viridis

The identity and amount of quinone in single crystals from reaction center protein from Rhodopseudomonas viridis have been determined using HPLC, optical spectroscopy and mass spectrometry. The ratio menaquinone‐9/ubiquinone‐9 for solutions of reaction center protein of Rps. viridis was 0.93 ± 0.05. After crystallization of the reaction center solution, the quinone ratio was 1.6 ± 0.1. These observations show that about half of the ubiquinone‐9 can be lost during crystallization.