Control of magnesium–protoporphyrin chelatase activity in Rhodopseudomonas spheroides. Role of light, oxygen, and electron and energy transfer

摘要

p1. Magnesium–protoporphyrin chelatase activity, previously shown in whole cells of iRhodopseudomonas spheroides/i, could not be demonstrated in cell-free extracts prepared in different ways, although spheroplasts retained moderate activity. Slight activity was detected also in whole cells of iRhodospirillum rubrum/i. 2. The effects on the activity of the enzyme of inhibitors of electron and energy transfer were studied in whole cells of iRps. spheroides/i. Amytal, rotenone, azide and cyanide inhibited at low ip/iOsub2/sub in the dark but not under anaerobic conditions in the light. Antimycin A and 2-heptyl-4-hydroxyquinoline iN/i-oxide, as well as uncouplers and oligomycin, inhibited under all environmental conditions. 3. The effects on magnesium chelatase activity of intermediates of the tricarboxylic acid cycle, of thenoyltrifluoroacetone, of a number of artificial electron donors or acceptors, of various quinones and of the oxidation–reduction indicator dyes Benzyl Viologen and Methyl Viologen are described. 4. It was concluded that electron transport between a ib/i-type and a ic/i-type cytochrome as well as associated energy conservation and transformation reactions were essential for activity. There was also a specific requirement for ATP. 5. Exogenous protoporphyrin and magnesium protoporphyrin monomethyl ester were incorporated into bacteriochlorophyll or late precursors by whole cells. 6. Evidence is presented that the insertion of magnesium was the only step inhibited by oxygen in the biosynthetic pathway between protoporphyrin and bacteriochlorophyll./p