Lecture 9

C2 cycle

Glycolate Pathway

Photosynthetic carbon oxidation cycle

• .035% CO2
• 21% Oxygen

Mutant can be considerably less fit for survival with decelerated growth.

Suppression of photorespiration by increasing CO2 levels from .035% to .1-.3% (increase by almost 100 fold)

Peroxisome (w/ catalase crystal), mitochondrion, and chloroplast.

Interaction between chloroplast and peroxisome where GLYCERATE is sent to chloroplast and 2 GLYCOLATE is sent to peroxisome.

• Glycerate used for R15BP synthesis.
• Glycolate used for a-ketoglutarate.

Glycine

2-phosphoglycolate -[phosphoglycolate phosphatase]-> glycolate + P

Glycolate + O2 -[glycolate oxidase]-> Glyoxylate + H2O2

*H2O2 -[catalase]-> (1/2)O2 + H2O

Glyoxylate -[A or B]-> Glycine

• A = Glutamate-glyoxylate aminotransferase; a-ketoglutarate
• B = Serine-glyoxylate aminotransferase; hydroxypyruvate

Serine (from mitochondrium) sent to peroxisome as 2 glycine (from peroxisome) sent to mitochondrium.

2 glycine used to generate NADH, CO2, NH4, and serine.

Oxidized, serine

2 Glycine -[Glycine decarboxylase-serine hydroxymethyl transferase complex]-> Serine

CO2, NH4, NADH formed

Glycine decarboxylase-serine hydroxymethyl transferase

assimilated in the chloroplast

Serine -[Serine glyoxylate aminotransferase]-> Hydroxypyruvate

Hydroxypyruvate -[hydroxypyruvate reductase; NADH]-> D-glycerate

~Chloroplast~

D-glycerate -[Glycerate kinase; ATP]-> 3-Phosphoglycerate

~Calvin Cycle~

Malate produced by chloroplast and mitochondrium is sent to the cytosol by the malate-oxaloacetate shuttle where it is turned to oxaloacetate and produces NADH

• 1. Help salvage carbon lost during rubisco oxygenase reaction
• tic
• 2. Protective function when dissipation of photosynthetic energy (ATP and reductant) is required.