Abstract
Chlorophyll b is synthesized from chlorophyll a by the oxidation of the methyl group on the ring B of the tetrapyrrole ring to the formyl group. Previously, we reported that chlorophyllide b could be converted to chlorophyll a in isolated cucumber etioplasts indicating the conversion of chlorophyll b to chlorophyll a. To identify the intermediate molecule, we used barley etioplasts instead of cucumber. Chlorophyll a and an additional pigment were found after incubation of chlorophyllide b with isolated barley etioplasts. The pigment has the same retention time and absorption spectrum as 7-hydroxymethyl chlorophyll, which has the hydroxymethyl group on ring B instead of the formyl group of chlorophyll b. Authentic 7-hydroxymethyl chlorophyll was prepared by reduction of chlorophyll b by NaBH4. Chlorophyll a accumulated during the incubation of 7-hydroxymethyl chlorophyllide with etioplasts. These findings indicate that chlorophyll b is converted to chlorophyll a via 7-hydroxymethyl chlorophyll. Chlorophyll b and 7-hydroxymethyl chlorophyll accumulated within a short period of incubation of chlorophyllide b with etioplasts. However, chlorophyll a accumulated with a concomitant decrease of chlorophyll b and 7-hydroxymethyl chlorophyll. These observations also suggest that chlorophyll b is converted to 7-hydroxymethyl chlorophyll and then to chlorophyll a. Both steps required ATP.
Highlights
The earliest precursor for chlorophyll (Chl),1 heme, and bilin synthesis is 5-aminolevulinic acid in higher plants, and the Chl branch of the pathway begins with insertion of magnesium into the protoporphyrin
Et al [6] have undertaken a systematic directed mutational analysis of 12 open reading frames to evaluate the role in photopigment biosynthesis of individual open reading frames and identified some genes required for synthesis of bacteriochlorophyll
Chlide b was incubated with cucumber etioplasts in the presence of S-[methyl-14C]adenosylmethionine as a methyl group donor
Summary
The earliest precursor for chlorophyll (Chl), heme, and bilin synthesis is 5-aminolevulinic acid in higher plants, and the Chl branch of the pathway begins with insertion of magnesium into the protoporphyrin. A 46-kilobase region of the Rhodobacter capsulatus contains most of the genetic loci involved in the magnesium branch of the bacteriochlorophyll biosynthetic pathway [3, 4]. This region has been sequenced, revealing the existence of 23 open reading frames [5]. Chl and bacteriochlorophyll are produced from the same precursors by a pathway which is conserved until its later stages. These findings with Rhodobacter are useful for the study of plant Chl synthesis. We reported the accumulation of Chl a during the incubation of chlorophyllide (Chlide) b with cucumber etioplasts in the dark indicating the conversion of Chl b to Chl a [11, 12]
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