BIOSYNTHESIS OF BACTERIOCHLOROPHYLL . CHARACTERIZATION OF LATTER STAGE INTERMEDIATES FROM MUTANTS OF RHODOPSEUDOMONAS SPHEROIDES

Various mutants of the nonsulfur purple bacterium, Rhodopseudomonas spheroides, unable to synthesize bacteriochlorophyll have been obtained which excrete tetrapyrrole pigments into the incubation medium. The pigments have been isolated, purified, and characterized chemically as magnesium 2,4-divinylpheoporphyrin a5, pheophorbide a, 2-devinyl-2-α-hydroxyethylchlorophyllide a, 2-desacetyl-2-α-hydroxyethylbacteriochlorophyllide, and bacteriochlorophyllide. The products accumulated by the various mutants indicate that the terminal steps of bacteriochlorophyll biosynthesis proceed in the following sequence: chlorophyllide a →2-devinyl-2-α-hydroxyethylchlorophyllide a→2-desacetyl-2-a-hydroxyethylbacteriochlorophyllide → bacteriochlorophyllide → bacteriochlorophyll. Compounds likely to be intermediates between magnesium protoporphyrin IX monomethyl ester and magnesium 2,4-divinylpheoporphyrin a5 and between the latter compound and chlorophyllide a have yet to be found in the photosynthetic bacteria. © 1969, American Chemical Society. All rights reserved.