}

Chlorophyll ''b'' is a form of

chlorophyll Chlorophyll is any of several related green pigments found in cyanobacteria and in the chloroplasts of algae and plants. Its name is derived from the Greek words (, "pale green") and (, "leaf"). Chlorophyll allows plants to absorb energy ...

. Chlorophyll ''b'' helps in

photosynthesis Photosynthesis ( ) is a system of biological processes by which photosynthetic organisms, such as most plants, algae, and cyanobacteria, convert light energy, typically from sunlight, into the chemical energy necessary to fuel their metabo ...

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. In

land plant The embryophytes () are a clade of plants, also known as Embryophyta (Plantae ''sensu strictissimo'') () or land plants. They are the most familiar group of photoautotrophs that make up the vegetation on Earth's dry lands and wetlands. Embryophyt ...

s, 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 Photosystem I (PSI, or plastocyanin–ferredoxin oxidoreductase) is one of two photosystems in the Light-dependent reactions, photosynthetic light reactions of algae, plants, and cyanobacteria. Photosystem I is an integral membrane ...

, there is a higher ratio of chlorophyll ''b'' to chlorophyll ''a''. This is adaptive, as increasing chlorophyll ''b'' increases the range of wavelengths absorbed by the shade chloroplasts.

Biosynthesis

The Chlorophyll ''b'' biosynthetic pathway utilizes a variety of

enzymes An enzyme () is a protein that acts as a biological catalyst by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as pro ...

. In most plants, chlorophyll is derived from

glutamate Glutamic acid (symbol Glu or E; known as glutamate in its anionic form) is an α-amino acid that is used by almost all living beings in the biosynthesis of proteins. It is a Essential amino acid, non-essential nutrient for humans, meaning that ...

and is synthesised along a branched pathway that is shared with

heme Heme (American English), or haem (Commonwealth English, both pronounced /Help:IPA/English, hi:m/ ), is a ring-shaped iron-containing molecule that commonly serves as a Ligand (biochemistry), ligand of various proteins, more notably as a Prostheti ...

and siroheme. The initial steps incorporate glutamic acid into 5-aminolevulinic acid (ALA); two molecules of ALA are then reduced to

porphobilinogen Porphobilinogen (PBG) is an organic compound that occurs in living organisms as an intermediate in the biosynthesis of porphyrins, which include critical substances like hemoglobin and chlorophyll. The structure of the molecule can be described ...

(PBG), and four molecules of PBG are coupled, forming protoporphyrin IX. Chlorophyll synthase is the enzyme that completes the biosynthesis of chlorophyll ''b'' by catalysing the reaction :chlorophyllide ''b'' + phytyl diphosphate

\rightleftharpoons

chlorophyll ''b'' + diphosphate This forms an ester of the carboxylic acid group in chlorophyllide ''b'' with the 20-carbon diterpene alcohol phytol.

References

{{DEFAULTSORT:Chlorophyll B Tetrapyrroles Photosynthetic pigments