Do you want to breathe?

     Does everyone like to breathe? Of course they do! Well, then everyone should love this protein. How is this protein important? Well, in order for there to be enough oxygen for everyone, plants, algae and bacteria need to be able to have oxygen evolving complexes, which break down water to form oxygen. However, for this to occur, there needs to be chlorophyll molecules to absorb photons. This is where this protein is important. It catalyzes the determining step in the production of chlorophyll. What happens is that there is a double bond in a molecule called protochlorophyllide. Once reduced to a single bond, the molecule is chlorophyllide, which is the direct precursor of chlorophyll. This is only the light-independent version of the protein. There is also a light-dependent version found in angiosperms (flowering plants) which requires light and light reactions to function.

                                          Chlorophyll

                                          Picture provided by http://www.secchidipin.org/chlorophyll.htm

  To put this all into perspective, most life could not occur without this protein. All of the reactions that occur in the membranes of chloroplasts could not occur. And as the light reactions of photosynthesis could not occur, ATP could not be made to power the Calvin-Benson Cycle. This means that CO2 could not be fixed by RuBisCO and sugars could not be made. This means that animals (including humans) would not have food. So next time you take a breath, eat some delicious food or even walk by a tree, remember to be thankful for light-independent protochlorophyllide reductase.

                                                          
                             Picture provided by http://www.co.marshall.ia.us/zenphoto/conservation/forest+floor.JPG.php

                     

The Light-Dependent and Light-Independent Reduction of Protochlorophyllide a to Chlorophyllide a

As it is known, a key reaction in the production of chlorophyll requires a reductase. This can be done in two ways; via a light reaction and a non-light reaction. This paper discusses the mechanism of these reactions and what molecules are involved in the reaction.


 http://www.springerlink.com/content/v82wn141907l5075/

A Prokaryotic Origin for Light-Dependent Chlorophyll Biosynthesis of Plants

The reduction of protochlorophyllide is important because it allows for the performance of photosynthesis by plants. This is catalyzed by either light dependent protochlorophyllide, found in angiosperms, or light-independent protochlorophyllide, found in gymnosperms, bacterium, etc. It has been found, however, that both of these enzymes are found in some bacteria, such as Synechocystis. It was found that the bacteria could produce chlorophyll in the light and that protochlorophyllide built up when in the dark, leading to the conclusion that the light-dependent version evolved not as a necessary function of land plants but as an accessory of bacteria.



http://www.jstor.org/stable/2367424?seq=1&Search=yes&searchText=reductase&searchText=protochlorophyllide&list=hide&searchUri=%2Faction%2FdoBasicSearch%3FQuery%3Dprotochlorophyllide%2Breductase%26acc%3Don%26wc%3Don&prevSearch=&item=1&ttl=269&returnArticleService=showFullText&resultsServiceName=null

Yellow-in-the-Dark Mutants of Chlamydomonas Lack the CHLL Subunit of Light-Independent Protochlorophyllide Reductase

A key step in the production of chlorophyll is the reduction of a double bond of an intermediate structure. This can be done by one of two ways; with light in angiosperms or without light in gymnosperms, cyanobacteria, etc. With light, the reaction can occur via a reductase. However, without light, the reaction requires the use of certain genes. In the bacteria Chlamydomonas reinhardtii, the genes ChlL, ChlN and ChlB and certain loci, y, must be present. The products of these genes are thought to be subunits of the enzyme Light-Independent Protochlorophyllide Reductase, which catalyzes the reduction of the double bond mentioned earlier. When reacted with light, it was found that the ChlL protein was inhibited. Also, the y genes were required for the production of the ChlL protein.

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