Chlorophyll b

Chemical compound From Wikipedia, the free encyclopedia

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 extra carbonyl group. Its color is green, and it primarily absorbs blue light.[2]

Quick facts Names, Identifiers ...
Chlorophyll b
Structure of β-Chlorophyll
Structure of β-Chlorophyll
Names
IUPAC name
Chlorophyll b
Systematic IUPAC name
Magnesium [methyl (3S,4S,21R)-14-ethyl-13-formyl-4,8,18-trimethyl-20-oxo-3-(3-oxo-3-{[(2E,7R,11R)-3,7,11,15-tetramethyl-2-hexadecen-1-yl]oxy}propyl)-9-vinyl-21-phorbinecarboxylatato(2-)-κ2N,N′]
Other names
β-Chlorophyll
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.007.522 Edit this at Wikidata
EC Number
  • 208-272-4
E number E140 (colours)
UNII
  • InChI=1S/C55H71N4O6.Mg/c1-12-38-35(8)42-27-43-36(9)40(23-24-48(61)65-26-25-34(7)22-16-21-33(6)20-15-19-32(5)18-14-17-31(3)4)52(58-43)50-51(55(63)64-11)54(62)49-37(10)44(59-53(49)50)28-46-39(13-2)41(30-60)47(57-46)29-45(38)56-42;/h12,25,27-33,36,40,51H,1,13-24,26H2,2-11H3,(H-,56,57,58,59,60,62);/q-1;+2/p-1/b34-25+;/t32-,33-,36+,40+,51-;/m1./s1 checkY
    Key: NSMUHPMZFPKNMZ-VBYMZDBQSA-M checkY
  • InChI=1S/C55H72N4O6.Mg/c1-12-38-35(8)42-27-43-36(9)40(23-24-48(61)65-26-25-34(7)22-16-21-33(6)20-15-19-32(5)18-14-17-31(3)4)52(58-43)50-51(55(63)64-11)54(62)49-37(10)44(59-53(49)50)28-46-39(13-2)41(30-60)47(57-46)29-45(38)56-42;/h12,25,27-33,36,40,51H,1,13-24,26H2,2-11H3,(H2,56,57,58,59,60,62);/q;+2/p-2/b34-25+;/t32-,33-,36+,40+,51-;/m1./s1
    Key: MSLKMRUEVOYOOZ-VBYMZDBQSA-L
  • CCC1=C(C2=NC1=CC3=C(C4=C([N-]3)C(=C5[C@H]([C@@H](C(=N5)C=C6C(=C(C(=C2)[N-]6)C=C)C)C)CCC(=O)OC/C=C(\C)/CCC[C@H](C)CCC[C@H](C)CCCC(C)C)[C@H](C4=O)C(=O)OC)C)C=O.[Mg+2]
Properties
C55H70MgN4O6
Molar mass 907.492 g·mol−1
Appearance Green
Odor Odorless
Melting point ~ 125 °C (257 °F; 398 K)[1]
Insoluble[1]
Solubility Very soluble in ethanol, ether, pyridine
Soluble in methanol[1]
Absorbance See text
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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The absorption spectrum of both the chlorophyll a and the chlorophyll b pigments. The use of both together enhances the size of the absorption of light for producing energy.

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.[3] This is adaptive, as increasing chlorophyll b increases the range of wavelengths absorbed by the shade chloroplasts.

Structure of chlorophyll b molecule showing the long hydrocarbon tail

Biosynthesis

Main article: Chlorophyllide

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.[5][6][7] 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[8] is the enzyme that completes the biosynthesis of chlorophyll b[9][10] by catalysing the reaction EC 2.5.1.62

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.

References

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