World Library  
Flag as Inappropriate
Email this Article

Turn over number

Article Id: WHEBN0002769021
Reproduction Date:

Title: Turn over number  
Author: World Heritage Encyclopedia
Language: English
Subject: BRENDA
Publisher: World Heritage Encyclopedia

Turn over number

Turnover number has two related meanings:

In enzymology, turnover number (also termed kcat) is defined as the maximum number of molecules of substrate that an enzyme can convert to product per catalytic site per unit of time and can be calculated as follows: kcat = Vmax/[E]T (see Michaelis-Menten kinetics). For example, carbonic anhydrase has a turnover number of 400,000 to 600,000 s−1, which means that each carbonic anhydrase molecule can produce up to 600,000 molecules of product (bicarbonate ions) per second.[1]

In other chemical fields, such as organometallic catalysis, turnover number (abbreviated TON) is used with a slightly different meaning: the number of moles of substrate that a mole of catalyst can convert before becoming inactivated. An ideal catalyst would have an infinite turnover number in this sense, because it wouldn't ever be consumed, but in actual practice one often sees turnover numbers which go from 100 up to 40 million for Catalase. The term turnover frequency (abbreviated TOF) is used to refer to the turnover per unit time, as in enzymology. For most relevant industrial applications, the turnover frequency is in the range of 10−2 - 102 s−1 (enzymes 103 - 107 s−1).[1] Turnover number of catalase is maximum i.e. 4 X 107 s−1.

Turnover number of acetylcholinesterase

Acetylcholinesterase (AChE) may be one of the fastest enzymes. It hydrolyzes acetylcholine to choline and an acetate group. One of the earliest values of the turnover number was 3 x 107 (molecules of acetylcholine) per minute per molecule of enzyme.[2] A more recent value at 25°C, pH = 7.0, acetylcholine concentration of 2.5 x 10−3 M, was found to be 7.4 x 105 min−1.[3]

There may be some 30 active centers per molecule.[4] AChE is a serine hydrolase that reacts with acetylcholine at close to the diffusion-controlled rate.[5]

See also


External links

de:Katalytische Produktivität
This article was sourced from Creative Commons Attribution-ShareAlike License; additional terms may apply. World Heritage Encyclopedia content is assembled from numerous content providers, Open Access Publishing, and in compliance with The Fair Access to Science and Technology Research Act (FASTR), Wikimedia Foundation, Inc., Public Library of Science, The Encyclopedia of Life, Open Book Publishers (OBP), PubMed, U.S. National Library of Medicine, National Center for Biotechnology Information, U.S. National Library of Medicine, National Institutes of Health (NIH), U.S. Department of Health & Human Services, and, which sources content from all federal, state, local, tribal, and territorial government publication portals (.gov, .mil, .edu). Funding for and content contributors is made possible from the U.S. Congress, E-Government Act of 2002.
Crowd sourced content that is contributed to World Heritage Encyclopedia is peer reviewed and edited by our editorial staff to ensure quality scholarly research articles.
By using this site, you agree to the Terms of Use and Privacy Policy. World Heritage Encyclopedia™ is a registered trademark of the World Public Library Association, a non-profit organization.

Copyright © World Library Foundation. All rights reserved. eBooks from Project Gutenberg are sponsored by the World Library Foundation,
a 501c(4) Member's Support Non-Profit Organization, and is NOT affiliated with any governmental agency or department.