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Chemistry Forums for Students => Physical Chemistry Forum => Topic started by: curiouscat on October 29, 2012, 03:15:25 PM

Title: SI unit of catalytic activity: Katal
Post by: curiouscat on October 29, 2012, 03:15:25 PM
Do any of you guys ever use this unit? It has always bugged me that it's been nominated an SI unit (no mean feat) and yet I never see it used.

Is there a niche sector that uses it?  ???

http://en.wikipedia.org/wiki/Katal

PS. If indeed no one wants it; why don't they get rid of it?  ::)
Title: Re: SI unit of catalytic activity: Katal
Post by: juanrga on October 30, 2012, 06:31:52 AM
Quote from: curiouscat on October 29, 2012, 03:15:25 PM
Do any of you guys ever use this unit? It has always bugged me that it's been nominated an SI unit (no mean feat) and yet I never see it used.

Is there a niche sector that uses it?  ???

http://en.wikipedia.org/wiki/Katal

PS. If indeed no one wants it; why don't they get rid of it?  ::)

New units, definitions, etc. are not adopted immediately because there is inertia on using the old units, but in the long run (years-decades) it is waited that will be broadly used.
Title: Re: SI unit of catalytic activity: Katal
Post by: Babcock_Hall on October 30, 2012, 09:07:37 AM
I frequently use enzyme units.  The katal is a pretty big number.  I could see using microkatals...
Title: Re: SI unit of catalytic activity: Katal
Post by: curiouscat on October 31, 2012, 08:34:21 AM
One thing that I didn't understand was how katals are to be measured / quantified. Say I did a Friedel Crafts and know my gmol / sec or gmol / ( gm.Catalyst sec) etc. how do I convert that into katals.

Unfortunately wikipedia wasn't very clear on it.
Title: Re: SI unit of catalytic activity: Katal
Post by: discodermolide on October 31, 2012, 12:06:51 PM
Can turnover numbers be applied to enzymatic systems?
Title: Re: SI unit of catalytic activity: Katal
Post by: vex on October 31, 2012, 12:38:09 PM
Quote from: discodermolide on October 31, 2012, 12:06:51 PM
Can turnover numbers be applied to enzymatic systems?

Yes, but only if you want to feel bad about yourself.

Enzyme turnover numbers and turnover frequencies usually dwarf molecular numbers by orders of magnitude (at least for the kinds of reactions I frequently study). I've been thinking about this for a day or two, and I find that turnover number and frequency are more useful values... I guess I don't get the katal. Is this concept more frequently used in a bio/biochem setting?
Title: Re: SI unit of catalytic activity: Katal
Post by: Babcock_Hall on October 31, 2012, 08:07:54 PM
Quote from: discodermolide on October 31, 2012, 12:06:51 PM
Can turnover numbers be applied to enzymatic systems?
The turnover number kcat is Vmax/[enzyme]total.  It expresses how well the enzyme works under conditions of saturating substrate.
Title: Re: SI unit of catalytic activity: Katal
Post by: Babcock_Hall on October 31, 2012, 08:15:57 PM
Quote from: curiouscat on October 31, 2012, 08:34:21 AM
One thing that I didn't understand was how katals are to be measured / quantified. Say I did a Friedel Crafts and know my gmol / sec or gmol / ( gm.Catalyst sec) etc. how do I convert that into katals.

Unfortunately wikipedia wasn't very clear on it.
"One katal of trypsin, for example, is that amount of trypsin which breaks a mole of peptide bonds per second under specified conditions."  So a katal is expressed in moles per second.  From the Wikipedia entry on enzyme units (an older way of expressing activity):  "1 U = 1/60 micro katal = 16.67 nano katal."  One reason why moles per second and µmol per minute were chosen and not a unit of concentration per unit time was to take the volume of the assay out of the math.

Units or katals are extensive quantities, and they are helpful in tracking the course of an enzyme purification.  You can often buy enzymes in terms of how many units of enzyme are present, such as 5000 units of pyruvate kinase.  Specific activity (units/mg protein) tell one a bit more about the purity and quality of an enzyme.