Pseudocyclic Photophosphorylation

 Amon et al.(1954) demonstrated yet another kind of phosphorylation. They observed that:

1. In the absence of CO2 and NADP, it can produce ATP from ADP and PI in the presence of FMN (Flavine Mono Nucleotide) or vitamin K and O2.

2. The process is very simple.

3. It requires no chemical change except for the formation of ATP and water.

4. This is also called Oxygen-dependent FMN catalyzed photophosphorylation or pseudocyclic photophosphorylation involving reduction of FMN with the production of O2.

II. PATH OF CARBON IN PHOTOSYNTHESIS (OR) DARK REACTION (OR) BLACKMAN’S REACTION
(Activities found in stroma).

The dark reaction of photosynthesis is purely enzymatic and slower than the primary photochemical reaction. It takes place in the stroma portion of chloroplast and is independent of light, i.e., it can occur either in the presence or absence of light. The main credit for investigating the sequences of dark reactions in photosynthesis goes to Melvin Calvin who was awarded Nobel Prize in 1961. A.A.Benson, J. Bassham, and other coworkers have also contributed a lot.

By employing labeled 14C in photosynthesis, Calvin and his co-workers were able to formulate the complete metabolic path of carbon assimilation in the form of a cycle, which is called as Calvin Cycle. They observed that carbon reduction is a cyclic process and the first stable product is the 3-C compound, i.e., 3-phosphoglyceric acid. The first acceptor of labeled CO2 was found to be a 5-carbon compound (ribulose 1,5-diphosphate; RuDP). The entire process of photosynthesis runs in a cyclic fashion, which includes the formation of hexose or starch and regeneration of RuDP.

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