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Chlorophyllide a, (R=H). In chlorophyllide b, the methyl group show in the green box is replaced with a formyl group. Chlorophyllide a, is a carboxylic acid (R=H). In chlorophyllide b, the methyl group at position 13 (IUPAC numbering for chlorophyllide a) and highlighted in the green box, is replaced with a formyl group.
This conversion forms an ester of the carboxylic acid group in chlorophyllide a with the 20-carbon diterpene alcohol phytol. Chlorophyll b is made by the same enzyme acting on chlorophyllide b. The same is known for chlorophyll d and f, both made from corresponding chlorophyllides ultimately made from chlorophyllide a. [39]
The Chlorophyll b biosynthetic pathway utilizes a variety of enzymes. [4] In most plants, chlorophyll is derived from glutamate and is synthesised along a branched pathway that is shared with heme and siroheme.
The enzyme that converts protochlorophyllide to chlorophyllide a, the next intermediate on the biosynthetic pathway, [4] is protochlorophyllide reductase, [5] EC 1.3.1.33. There are two structurally unrelated proteins with this activity: the light-dependent and the dark-operative. The light-dependent reductase needs light to operate.
Chlorophyll a is a specific form of chlorophyll used in oxygenic photosynthesis.It absorbs most energy from wavelengths of violet-blue and orange-red light, and it is a poor absorber of green and near-green portions of the spectrum. [3]
Chlorophyllide, the product of the reaction catalyzed by chlorophyllase, spontaneously combines with plant lipids such as phosphatidylcholine liposomes along with sulfoquinovosyl diacylglycerol. These two lipids cooperatively inhibit the activity of chlorophyllase, but this inhibition can be reversed by the presence of Mg++, a divalent cation. [10]
In enzymology, chlorophyll synthase (EC 2.5.1.62) is an enzyme that catalyzes the chemical reaction. chlorophyllide a + phytyl diphosphate chlorophyll a + diphosphate. The two substrates of this enzyme are chlorophyllide a and phytyl diphosphate; its two products are chlorophyll a and diphosphate.
The bacteriochlorin-cored BChls a, b, g require a unique step to reduce the double bound between C7 and C8, which is performed by Chlorophyllide a reductase (COR). [9] Isobacteriochlorins, in contrast, are biosynthesised from uroporphyrinogen III in a separate pathway that leads, for example, to siroheme, cofactor F 430 and cobalamin.