{"606884":{"#nid":"606884","#data":{"type":"news","title":"Making the Oxygen We Breathe, a Photosynthesis Mechanism Exposed","body":[{"value":"\u003Cp\u003EArguably, the greatest fueler of life on our planet is photosynthesis, but understanding its labyrinthine chemistry, powered by sunlight, is challenging. Researchers recently illuminated some new steps inside the molecular factory that makes the oxygen we breathe.\u003Cbr \/\u003E\r\n\u003Cbr \/\u003E\r\nThough chlorophyll is the best-known part, for the vivid green it colors nature, many compounds work together in photosynthesis. And Georgia Tech chemists devised clever experiments to inspect a small metal catalyst and an amino acid intimately involved in the release of O\u003Csub\u003E2\u003C\/sub\u003E from water\u0026nbsp;in what\u0026#39;s known as photosystem II (PSII).\u0026nbsp;\u003Cbr \/\u003E\r\n\u003Cbr \/\u003E\r\nPSII is a complex protein structure found in plants and algae. It has a counterpart called\u0026nbsp;photosystem I, an equally complex light-powered producer of oxygen and biomaterials.\u003C\/p\u003E\r\n\r\n\u003Ch4\u003E\u003Cstrong\u003EPhotosynthesis Q \u0026amp; A\u003C\/strong\u003E\u003C\/h4\u003E\r\n\r\n\u003Cp\u003ESome questions and answers below will help elucidate the researchers\u0026rsquo; findings about\u0026nbsp;O\u003Csub\u003E2\u003C\/sub\u003E production inside PSII.\u003C\/p\u003E\r\n\r\n\u003Cp\u003E\u0026ldquo;Photosynthesis in plants and algae can be compared to an artificial solar cell,\u0026rdquo; said principal investigator \u003Ca href=\u0022http:\/\/www.chemistry.gatech.edu\/faculty\/barry\/\u0022 target=\u0022_blank\u0022\u003EBridgette Barry\u003C\/a\u003E, who is a \u003Ca href=\u0022http:\/\/www.chemistry.gatech.edu\/\u0022 target=\u0022_blank\u0022\u003Eprofessor in Georgia Tech\u0026rsquo;s School of Chemistry and Biochemistry\u003C\/a\u003E. \u0026ldquo;But, in photosynthesis, light energy fuels the production of food (carbohydrates) instead of charging a battery. O\u003Csub\u003E2\u003C\/sub\u003E is released from water as a byproduct.\u0026rdquo;\u003C\/p\u003E\r\n\r\n\u003Cp\u003EBarry, first author Zhanjun Guo, and researcher Jiayuan He \u003Ca href=\u0022http:\/\/www.pnas.org\/content\/early\/2018\/05\/10\/1800758115\u0022 target=\u0022_blank\u0022\u003Epublished their research on May 11, 2018, in the journal \u003Cem\u003EProceedings of the National Academy of Sciences\u003C\/em\u003E\u003C\/a\u003E. Their work was funded by the National Science Foundation.\u003C\/p\u003E\r\n\r\n\u003Ch4\u003E\u003Cstrong\u003EHow does photosynthesis II release oxygen from water?\u003C\/strong\u003E\u003C\/h4\u003E\r\n\r\n\u003Cp\u003EMany details are still unknown, but here are some basic workings that were already well-established going into this new study.\u003C\/p\u003E\r\n\r\n\u003Cp\u003EPS II is a biochemical complex made mostly of large amino acid corkscrew cylinders and some smaller such cylinders strung together with amino acid strands. The reaction cycle that extracts the O\u003Csub\u003E2\u003C\/sub\u003E from H\u003Csub\u003E2\u003C\/sub\u003EO occurs at a\u0026nbsp;tiny spot, which the study focused on.\u003C\/p\u003E\r\n\r\n\u003Cp\u003EFor scale, if PSII were a fairly tall, very wide building, the spot might be the size of a large door in about the lower center of the building, and the metal cluster would be located there. Intertwined in the proteins would be sprawling molecules that include beta-carotene and chlorophyll, a great natural photoelectric semiconductor.\u003C\/p\u003E\r\n\r\n\u003Cp\u003E\u0026ldquo;Photons from sunlight bombard photosystem II and displace electrons in the chlorophyll,\u0026rdquo; Barry said. \u0026ldquo;That creates moving negative charges.\u0026rdquo;\u003C\/p\u003E\r\n\r\n\u003Ch4\u003E\u003Cstrong\u003EWhat is the metal catalyst?\u003C\/strong\u003E\u003C\/h4\u003E\r\n\r\n\u003Cp\u003EThe metal catalyst acts like a \u003Ca href=\u0022https:\/\/www.khanacademy.org\/science\/physics\/circuits-topic\/circuits-with-capacitors\/v\/capacitors-and-capacitance\u0022 target=\u0022_blank\u0022\u003Ecapacitor\u003C\/a\u003E, building up charge that it uses to expedite four chemical reactions that release the O\u003Csub\u003E2\u003C\/sub\u003E by removing four electrons, one-by-one, from two water molecules. In the process, water also spins off four H+ ions, i.e. protons, from two H\u003Csub\u003E2\u003C\/sub\u003EO molecules.\u003C\/p\u003E\r\n\r\n\u003Cp\u003EAn additional highly reactive compound near the metal cluster acts as a \u0026quot;switch\u0026quot; to drive the electron movement in each step of the reaction cycle. It\u0026#39;s a common amino acid called tyrosine, a little building block on that mammoth protein building.\u003C\/p\u003E\r\n\r\n\u003Ch4\u003E\u003Cstrong\u003EWhat does the \u0026lsquo;switch\u0026rsquo; do?\u003C\/strong\u003E\u003C\/h4\u003E\r\n\r\n\u003Cp\u003EThis is where the new study\u0026rsquo;s insights come in to describe details of what\u0026#39;s going on between the tyrosine and the cluster.\u003C\/p\u003E\r\n\r\n\u003Cp\u003EThe light reactions remove one electron from tyrosine, making it what\u0026rsquo;s called an unstable \u003Ca href=\u0022https:\/\/en.wikipedia.org\/wiki\/Radical_(chemistry)\u0022 target=\u0022_blank\u0022\u003Eradical\u003C\/a\u003E, and the radical version of tyrosine strongly attracts a new electron.\u003C\/p\u003E\r\n\r\n\u003Cp\u003EIt very quickly gets that new electron from the metal cluster. As PSII absorbs photons, the taking of an electron from tyrosine and its radical\u0026rsquo;s grabbing of a new one from the cluster repeats rapidly, making the tyrosine a kind of flickering switch.\u003C\/p\u003E\r\n\r\n\u003Cp\u003E\u0026ldquo;The tyrosine radical drives the cycle around, and what they (Guo and He) did in the lab was to develop a way of seeing the radical reaction in the presence of the metal cluster,\u0026rdquo; Barry said.\u003C\/p\u003E\r\n\r\n\u003Cp\u003EGuo and He also found that the calcium atom in the cluster has key interactions with tyrosine.\u003C\/p\u003E\r\n\r\n\u003Ch4\u003E\u003Cstrong\u003EHow did they observe that single chemical component in a living system?\u003C\/strong\u003E\u003C\/h4\u003E\r\n\r\n\u003Cp\u003EFiguring out how to make the reactions observable was painstaking. The researchers isolated some PSII from spinach, and they slowed it way down by cooling it in the dark.\u003C\/p\u003E\r\n\r\n\u003Cp\u003EThen they gave it a burst of red light to prepare one step in the reaction cycle, then a green flash to take the electron from tyrosine. Then the electrons slowly returned to the tyrosine.\u003C\/p\u003E\r\n\r\n\u003Cp\u003EThe researchers observed the processes via \u003Ca href=\u0022https:\/\/study.com\/academy\/lesson\/vibrational-spectroscopy-definition-types.html\u0022 target=\u0022_blank\u0022\u003Evibrational spectroscopy\u003C\/a\u003E, which revealed qualities of tyrosine\u0026rsquo;s chemical bonds. The researchers also examined the calcium and discovered a special interaction between it and tyrosine.\u003C\/p\u003E\r\n\r\n\u003Cp\u003E\u0026ldquo;A new thing we saw was that the calcium ion made the tyrosine twist a certain way,\u0026rdquo; Barry said. \u0026ldquo;It turns out that the tyrosine may be a very flexible switch.\u0026rdquo;\u003C\/p\u003E\r\n\r\n\u003Cp\u003EThe researchers also swapped out calcium for other metals and found that the calcium fulfills this role quite optimally.\u003C\/p\u003E\r\n\r\n\u003Ch4\u003E\u003Cstrong\u003ESo, why is understanding photosynthesis important?\u003C\/strong\u003E\u003C\/h4\u003E\r\n\r\n\u003Cp\u003E\u0026ldquo;Oxygen photosynthesis really is the great fueler life on our planet,\u0026rdquo; Barry said.\u003C\/p\u003E\r\n\r\n\u003Cp\u003EAbout two billion years ago, the photosynthesis that generates O\u003Csub\u003E2\u003C\/sub\u003E exploded, and as breathable oxygen filled Earth\u0026rsquo;s oceans and atmosphere, life began evolving into the complex variety we have today. There are also pragmatic reasons for studying photosynthesis.\u003C\/p\u003E\r\n\r\n\u003Cp\u003E\u0026ldquo;You could work with it to make crops more productive,\u0026rdquo; Barry said. \u0026ldquo;We may have to repair and adapt the photosynthesis process someday, too.\u0026rdquo;\u003C\/p\u003E\r\n\r\n\u003Cp\u003EEnvironmental stresses could possibly weaken photosynthesis in the future, calling for biochemical tweaks. Also, natural photosynthesis is an exceptionally good model for photoelectric semiconductors like those used in emerging energy systems.\u003C\/p\u003E\r\n\r\n\u003Cp\u003E\u003Cstrong\u003E\u003Cem\u003ELike this article?\u0026nbsp;\u003Ca href=\u0022http:\/\/www.rh.gatech.edu\/subscribe\u0022 target=\u0022_blank\u0022\u003EGet our email newsletter here.\u003C\/a\u003E\u003C\/em\u003E\u003C\/strong\u003E\u003C\/p\u003E\r\n\r\n\u003Cp\u003E\u003Cem\u003EThe research was funded by the National Science Foundation (grant MCB-14-11734). Any opinions, findings and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect views of the National Science Foundation.\u003C\/em\u003E\u003C\/p\u003E\r\n\r\n\u003Cp\u003E\u003Cstrong\u003EMedia Relations Contact\u003C\/strong\u003E: Ben Brumfield (404-660-1408) (ben.brumfield@comm.gatech.edu).\u003C\/p\u003E\r\n\r\n\u003Cp\u003E\u003Cstrong\u003EWriter\u003C\/strong\u003E: Ben Brumfield\u003C\/p\u003E\r\n","summary":null,"format":"limited_html"}],"field_subtitle":"","field_summary":[{"value":"\u003Cp\u003EOxygen photosynthesis has to be the greatest giver of life on Earth, and researchers have cracked yet another part of its complex but efficient chemistry. The more we know about it, the better we may be able to tweak photosynthesis, if it comes under environmental duress. It\u0026#39;s also a great teacher of how to harvest\u0026nbsp;sheer unlimited energy from the sun.\u003C\/p\u003E\r\n","format":"limited_html"}],"field_summary_sentence":[{"value":"Life on Earth as we know it never would have existed without oxygen photosynthesis, and researchers have cracked a new part of its code."}],"uid":"31759","created_gmt":"2018-06-11 16:05:57","changed_gmt":"2018-06-27 13:43:57","author":"Ben Brumfield","boilerplate_text":"","field_publication":"","field_article_url":"","dateline":{"date":"2018-06-11T00:00:00-04:00","iso_date":"2018-06-11T00:00:00-04:00","tz":"America\/New_York"},"extras":[],"hg_media":{"606869":{"id":"606869","type":"image","title":"Photosystem II artwork","body":null,"created":"1528729369","gmt_created":"2018-06-11 15:02:49","changed":"1528729406","gmt_changed":"2018-06-11 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