Studies on electron transfer systems in the marine diatom Phaeodactylum tricornutum. II. Identification and determination of quinones, cytochromes, and flavins.

Quinones constituting the electron transfer systems in a marine unicellular diatom, Phaeodactylum tricornutum, were isolated and identified chromatographically. The alga contained five quinones, i.e., plastoquinone A, plastoquinone C, plastoquinone D, alpha-tocopherylquinone, and ubiquinone-9. Other types of quinones, such as vitamin K1, were not detected. The contents of plastoquinone A, plastoquinone C, plastoquinone D, ubiquinone-9, and alpha-tocopherylquinone were 25.5, 4.95, 1.99, 4.78, and 0.28 mmol per mol of chlorophyll, respectively. The contents of the soluble C-type cytochromes, cytochrome c-550 and cytochrome c-553, were 2.15 and 4.34 mmol (heme basis) per mol of chlorophyll, respectively. The amount of B-type cytochrome in the bound form was estimated to be 3.24 mmol (heme basis) per mol of chlorophyll. The acid-soluble flavins, FAD and FMN, were present in amounts of 0.68 and 0.41 mmol per mol of chlorophyll, respectively.