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UniProt release 2013_07

Published June 26, 2013

Headline

How to go green, or red?

Chlorophyll is the major photosynthetic pigment. It performs the essential processes of harvesting light energy in the antenna complexes and transferring this energy to the reaction centers to produce chemical energy.

The chlorophyll molecule is present in all photosynthetic organisms. It is made up of 2 moieties of distinct origin, chlorophyllide and phytol. The early enzymatic steps of chlorophyllide biosynthesis from glutamyl-tRNA to protoporphyrin IX are shared with the heme biosynthesis pathway. Hence, protoporphyrin IX is the last common reactant for the synthesis of both heme and chlorophyll. To produce chlorophyll, a magnesium chelatase (EC=6.6.1.1) inserts Mg(2+) into the protoporphyrin IX ring, while an iron chelatase (EC=4.99.1.1) inserts Fe(2+) into the ring during heme biosynthesis.

In Arabidopsis thaliana, there are 15 enzymes and 27 genes required for chlorophyll biosynthesis from glutamyl-tRNA to chlorophyll b. Nine proteins are encoded by single-copy genes, and the others are encoded by gene families consisting of two to three members. The magnesium chelatase is a complex of three subunits, CHLI, CHLD and CHLH encoded by 4 different genes. As of this release, all 27 proteins are manually annotated in UniProtKB/Swiss-Prot. They all contain the subtopic PATHWAY: Porphyrin-containing compound metabolism; chlorophyll biosynthesis in ‘General annotation (Comments)’ and the keyword Chlorophyll biosynthesis. This keyword also allows the retrieval of additional proteins involved in the regulation of the process or in the biosynthesis of the long phytol side chain, for example.

Enzymes involved in the biosynthesis of the porphyrins, common to both heme and chlorophyll, are also annotated with the comment PATHWAY: Porphyrin-containing compound metabolism; protoporphyrin-IX biosynthesis.

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