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Four-Electron Reduction of Dioxygen to Water
The four-electron reduction for Ascorbate oxidase starts with the enzyme in its resting (oxidized) form undergoing a one-electron reduction. The electron for the reduction is provided by the substrate L-ascorbate and donated to the type 1 copper; the primary electron acceptor.

Afterwards, as evident by pulse-radiolysis studies, an intramolecular electron-transfer occurs where an electron is transferred from type 1 copper center to the trinuclear cluster. Trinuclear cluster contains three copper atoms; 1 pair of type 3 copper atoms (CU2 and CU3) and a type 2 copper center (CU4). The substrate, L-ascorbate is oxidized which leads to the formation and disappearance of ascorbate free radical (semidehydroascorbate radical) which spontaneously dismutates.

After four electrons have been transferred by four sequential one-electron reduction, the enzyme is fully reduced. Studies on how the intramolecular electron transfer between the copper centers (type 1 copper to the tri-nuclear cluster) in the enzyme indicate that the electron transfer is greater the more electrons are provided to the enzyme beforehand. The fully reduced enzyme is returned back to its resting (oxidized) form by a four-electron reduction reaction with dioxygen to form water.

A proposed method for the formation of water starts with di-oxygen binding to type 2 copper center (CU4) in the trinuclear cluster followed by a transfer for two electrons from the pair of type 3 copper atoms (CU2 and CU3) which leads to the formation of a hydroperoxide intermediate. A third electron and fourth electron are transferred to the hydrogen peroxide intermediate from the type 2 copper center in the cluster and the type 1 copper, respectively which results in the O-O bond being broken and a water molecule being released.

Structure of L-Ascorbate Oxidase
Ascorbate oxidase is a homodimeric enzyme containing subunits of Mr = 70 000. Each subunit in the enzyme has 552 amino acid residues, which have a globular shape and are built up by three domains with similar β-barrel folding. The active site contains a type 1 copper separated by about 12.5 Å from a trinuclear copper cluster. The type 1 copper contains four amino acid ligands (two histidine N-donors, a cysteine thiolate S-donor and methionine thioether S-donor). The trinuclear cluster contains three copper atoms; 1 pair of type 3 copper atoms and a type 2 copper center. In total, the trinuclear cluster has eight histidine ligands. The pair of type 3 copper atoms are each coordinated to three histidines and bridged by a hydroxide group while the type 2 copper center is coordinated to two histidine ligands and a terminal hydroxide ligand. The average copper–copper distance in the trinuclear cluster is 3.74 Å.

Catalytic Mechanism for Reduction of Di-Oxygen to Water
The Catalytic mechanism for Ascorbate oxidase starts with the enzyme in its resting (oxidized) form undergoing a one-electron reduction. The electrons for the reduction are provided by the substrate L-ascorbate and donated to the type 1 copper; the primary electron acceptor, in a fast, bimolecular second-order reaction. As a result, L-ascorbate is oxidized to semidehydroascorbate radical and spontaneously dismutates. The electrons are then transferred from type 1 copper to the trinuclear cluster. After four electrons have been transferred by the sequential one-electron reduction, the enzyme is fully reduced. In this state, the hydroxyl bridge between the type 3 coppers has been released and the copper–copper distances in the trinuclear cluster increase to an average  4.1–5.1 Å. In order to convert the fully reduced enzyme back to its resting (oxidized) form, dioxygen reacts with the reduced enzyme to form a peroxide-level intermediate. Upon reduction of dioxygen, the enzyme which is produced can relax to the resting state or is reduced by other substrate molecules for further turnover.

Properties of Dibutyltin Diacetate

 * molecular formula:
 * molar mass: 351.03 g mol-1
 * m.p. : 7-10 °C
 * b.p. : 142-145 °C 10 mm Hg
 * solubility in water: 0.006 g L-1

dibutyltin diacetate

Related compound

Dibutyltin diacetate

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Critique of Carbonic Anhydrase Mechanism Figure
Figure does not have sufficient detail.

1.8. Practice entering a formula
$$3/2=2^2+a_2$$

Practice Using History Pages, Talk pages, Article ratings and Watchlists
The main purpose of these two edits by Smokefoot is to make the added info by Ninja Recs to appear more like a compilation of facts rather then a school essay and to remove conventional essay introductory sentences.

The statistics for these edits are negative numbers because information is being removed from the article. The negative red numbers (-xx) indicate the number of bytes that have been removed.

Wikipedia “Iron–sulfur cluster” article: Talk page discussion of Dec 4th / 5th 2018 edits
Proposal[edit]

Hello,

I hoping to contribute, my knowledge to this article by discussing the strength, covalency and electron transfer effects. Ninja Recs (talk) 01:00, 12 October 2018 (UTC)[ reply]


 * You are writing at a level that indicates that your teacher is needed. Please ask your teacher to read some Wikipedia articles first. --Smokefoot (talk) 01:20, 5 December 2018 (UTC)[ reply]
 * Ninja Recs's Instructor gave 58 revisions to make to this contribution before moving to the live article however, regrettably, none of them were made --Kcsunshine999 (talk) 22:46, 5 September 2021 (UTC)[ reply]

Merge proposal, withdrawn[edit]

I propose to merge this article with the one on Iron-sulfur protein. Adding to the confusion, we also have an article on ferredoxin, which I propose to leave alone. --Smokefoot (talk) 22:42, 30 December 2007 (UTC)[ reply]

I dont think it should be totally merged since organometallic iron sulfur clusters are not biological and should not be mentioned in the iron-sulfur protein article. But the synthetic iron sulfur clusters (like those from Richard Holm at Harvard) should be moved to the iron-sulfur protein article since they are meant to be biomimetic analogs of the biological clusters. Conversely, there should be very little, almost no, discussion of the biological iron sulfur clusters in this article since that is redundant with the iron-sulfur proteins article, so the two sections should be merged and have only one or two sentences with an internal link to the iron-sulfur proteins article. I also dont think this article is very worthwhile since i dont think there are enough non-biological iron sulfur clusters, Im surprised this article was started in the first place. Kcsunshine999 (talk) 05:43, 11 December 2018 (UTC)[ reply]


 * Agreed.--Smokefoot (talk) 10:54, 11 December 2018 (UTC)[ reply]

Wikipedia “Carbonic anhydrase” article: Talk page discussion of Dec 4th / 5th 2018 edits
the main purpose of these three edits by Smokefoot was to remove some redundant information, remove info that is not directly related to the mechanism and to remove repeated reference.

The negative signs in the statistics mean indicating information is being removed from the article. The negative red number (-xx) indicates the number of bytes that have been removed.

The line 26 second box edit by Smokefoot on 12:03 Dec 3 2018 is a good improvement to the Introduction compared to the previous version because it removes some redundant information about history of discovery of enzyme and removes subjective language; 'most important function of this enzyme' and "is one of the fastest of all enzymes".

The new paragraph added in line 32 made on Nov 28 2019 by Bilal.bhatti, makes a good improvement to the Introduction because in the first sentence it clearly states the specific function of the enzyme and its function in different parts of the human body. The current version of the carbonic anhydrase article still contains the paragraph added by Bilal.bhatti.

There has been enough useful discussion about what needs to be done to improve the carbonic anhydrase article.

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