Chlorophyll b
Chlorophyll b is a form of chlorophyll. Chlorophyll b helps in photosynthesis by absorbing light energy. It is more soluble than chlorophyll a in polar solvents because of its carbonyl group. Its color is green, and it primarily absorbs blue light.[1]
In land plants, the light-harvesting antennae around photosystem II contain the majority of chlorophyll b. Hence, in shade-adapted chloroplasts, which have an increased ratio of photosystem II to photosystem I, there is a higher ratio of chlorophyll b to chlorophyll a.[2] This is adaptive, as increasing chlorophyll b increases the range of wavelengths absorbed by the shade chloroplasts.
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| Structure of chlorophyll b molecule showing the long hydrocarbon tail | |
Biosynthesis
Template:Main The Chlorophyll b biosynthetic pathway utilizes a variety of enzymes.[3] In most plants, chlorophyll is derived from glutamate and is synthesised along a branched pathway that is shared with heme and siroheme.[4][5][6] The initial steps incorporate glutamic acid into 5-aminolevulinic acid (ALA); two molecules of ALA are then reduced to porphobilinogen (PBG), and four molecules of PBG are coupled, forming protoporphyrin IX.
Chlorophyll synthase[7] is the enzyme that completes the biosynthesis of chlorophyll b[8][9] by catalysing the reaction Template:EC number
- chlorophyllide b + phytyl diphosphate chlorophyll b + diphosphate
This forms an ester of the carboxylic acid group in chlorophyllide b with the 20-carbon diterpene alcohol phytol.