Elementary plant Biochemistry and Biotechnology (2+1)

Chlorophylls

• Chlorophylls occur in the photosynthetic pigment system as chromoproteins (pigment – protein complexes). In the case of chlorophylls and carotenoid, the pigment – protein linkage is relatively weak, being composed of non-covalent bonds. Those bonds are easily broken. Hence chlorophylls and carotenoids can be extracted simply by macerating the plant tissue with an organic solvent such as acetone. However, the linkage between phycobilins and protein is covalent and occurs as phycobiliproteins.


• The phycobiliproteins are water – soluble.Four different chlorophylls have been extracted from plants. Chlorophyll b is almost as widespread but is absent in all the algae except few. Chlorophyll c1 and c2 are known. Chlorophyll d is also noticed.Chlorophyll is a tetrapyrrole and the four atoms of the pyrroles are coordinated to a magnesium atom. Thus chlorophyll is a magnesium – porphyrin

Absorption spectra of chlorophylls

• The absorption spectra of Chl a and b are different. Light that is not appreciably absorbed by chlorophyll a at 460 nm, is absorbed by chlorophyll b. Thus these two kinds of chlorophylls complement each other in absorbing the incident sunlight. These chlorophylls are very effective photoreceptors because they contain networks of alternating single and double bonds (conjugated)