Photorespiration

The desired reaction is the addition of carbon dioxide to RuBP (carboxylation), a key step in the Calvin–Benson cycle, however approximately. Biological adaptation to. It begins when rubisco acts on oxygen instead of carbon dioxide.

How the Cand CAM pathways help minimize photorespiration. Phosphoglycolate formed by oxygen fixation is recycled to the Calvin cycle intermediate . Because in photosynthesis carbon dioxide is .

While this efficiency is impressive, it also is rarely achieved. The difficulty is in the protein that carries out the first step of photosynthesis. Photorespiration takes place in green plants at the same time that photosynthesis does.

Molecular oxygen, O competes with CO for the active site of ribulose bisphosphate carboxylase, leading to an oxidation and loss of the ribulose bisphosphate . The process by which in the presence of light plant consumes oxygen and releases carbon dioxide (in stead of fixing carbon dioxide) during photosynthesis, resulting in a decrease in photosynthetic output since no ATP is produced and carbon (as well as nitrogen in the form of ammonia) is lost inevitably . All plants carry on photosynthesis by. CO2) to a phosphorylated 5-carbon sugar called ribulose bisphosphate. The resulting 6-carbon compound breaks down into .

When ribulose-5-biphopshate (RuBP) is carboxylate it reacts with carbon dioxide and water to give two glycerate-3- phosphate (GP) molecules, which can be utilised in the. But this reaction is very slow at low carbon dioxide concentrations. Cplants have the disadvantage that in hot dry conditions their photosynthetic efficiency suffers because of a process called photorespiration. Rubisco also catalyses . When the COconcentration in the chloroplasts drops below about ppm, the catalyst rubisco that helps to fix carbon begins to fix oxygen instead.

The photorespiratory carbon oxidation (PCO) cycle involves movement of metabolites between chloroplasts, peroxisomes and mitochondria. This is highly wasteful of the. Original drawing courtesy lan Woodrow). A scheme for photorespiration involving the photosynthetic carbon reduction (PCR) cycle and the photosynthetic carbon oxidation (PCO) . Sage, and Ferit Kocacinar . Cam plants avoid photorespiration by two mechanisms: 1) PEP carboxylase, and 2) a separation in time of carbon fixation and the Calvin cycle (light independent reactions).

However, recent research highlights the importance of photorespiration as a recycling pathway for the products of ribulose-5-bisphosphate (RuBP) oxygenation and its intimate . In Cterrestrial higher plants the flux through glycine and serine is so large that it in the production of ammonia at a rate far exceeding that from reduction of new nitrogen entering the plant. As its name suggests (rubsiCO ) the enzyme is both a carboxylase and an oxygenase. The active site of rubisco cannot distinguish the two similar substrates: O=C=O and O=O.

Unlike tobacco, the photorespiration by maize was much slower than its dark respiration, being only as fast in this experiment. If tobacco tissue was darkened at zero time in the 1“C assay, instead of after the usual period in the light in CO,-free air, after minutes (post-illumination outburst) the “COreleased in the .