The derivation of the oxygen atoms of the 13¹‐oxo and 3‐acetyl groups of bacteriochlorophyll a from water in Rhodobacter sphaeroides cells adapting from respiratory to photosynthetic conditions: evidence for an anaerobic pathway for the formation of isocyclic ring E

Abstract

Using mass spectrometry, we have demonstrated ~sO-labelling of both the 13Loxo and 3-acetyl groups of newly-formed bacteriochlorophyll a synthesized by Rhodobacter sphaeroides cells during adaptation from respiratory to photosynthetic conditions in the presence of H21so. This derivation of the 131-oxo group of bacteriochlorophyll a from water provides a stark contrast with that of chlorophylls in higher plants where ring E formation is an aerobic process in which the 13Loxo group arises from molecular oxygen via an oxygenase activity. The formation of the 3-acetyl group of bacteriochlorophyll a, however, is consistent with the enzymic hydration of the 3-vinyl group of a derivative of chlorophyll a.

Light-harvesting Chlorophyll a/b-binding Protein Stably Inserts into Etioplast Membranes Supplemented with Zn-pheophytina/b

“…A third possibility is that some of the Zn-phe a synthesized in situ is converted into Zn-phe b. It has been shown recently that Chl b is formed from Chl a by oxidation with molecular oxygen, a reaction that requires a highly hydrophobic environment and suggests that Chl a is converted as it is already bound in a pigment-protein complex (36). We have no information as to whether part of the Zn-phe a in our experiments is oxidized to Zn-phe b.…”

Biosynthesis of the 3‐Acetyl and 131‐Oxo Groups of Bacteriochlorophyll a in the Facultative Aerobic Bacterium, Rhodovulum sulfidophilum

“…This article is dedicated to Prof. Wolfhart Rüdiger on the occasion of his 65th birthday. the facultative photosynthetic bacterium, Rhodobacter sphaeroides, which forms BChl a in both strictly anaerobic conditions in the light and in atmospheres containing up to 6% oxygen in the dark [5].The 13 1 -oxo group of BChl a was also derived from water via a hydratase mechanism in R. sphaeroides [4,6]. In R. denitrificans, however, the 13 1 -oxo group was derived only from molecular oxygen via an oxygenase [4] as also occurs in chlorophyll (Chl) a and Chl b formation in green plants [7Ϫ9] and green algae [10].…”

“…The 13 1 -oxo group of BChl a was also derived from water via a hydratase mechanism in R. sphaeroides [4,6]. In R. denitrificans, however, the 13 1 -oxo group was derived only from molecular oxygen via an oxygenase [4] as also occurs in chlorophyll (Chl) a and Chl b formation in green plants [7Ϫ9] and green algae [10].…”

“…The ethereal pigment solution was dried with solid NaCl, decanted, and the solvent removed at about 40°on a rotary evaporator in vacuo. For MS analysis, the pigments were dissolved in a little toluene and dried by evaporation before isolating the BChl a from carotenoids [6] on a small (5 cmϫ0.2 cm) column of a DEAE-cellulose in CHCl 3 prepared as described by Sato and Murata [15] ; the BChl a was again dried with toluene before mass spectrometry.…”

“…BChl a was reduced in ethanol with 75 mM NaBH 4 : under these conditions, the 13 1 -oxo group of BChl a is not reduced [16]. The [3 1 hydroxy]-BChl a so formed was purified on DEAE-cellulose columns as previously described [6].…”