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bacteriochlorophyll A form of chlorophyll found in photosynthetic bacteria, notably the purple and green bacteria. There are several types, designated a to g. For example, bacteriochlorophyll a and bacteriochlorophyll b are structurally similar to the chlorophyll a and chlorophyll b found in plants; the purple bacteria contain either of these two types of bacteriochlorophyll, depending on the species. Bacteriochlorophyll is located in specialized membrane systems (chromatophores); in purple bacteria these are in the form of sheets, tubes, or vesicles arising inside the cell from the plasma membrane, whereas in green bacteria they are cylindrical structures (chlorosomes) underlying the plasma membrane.