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one unit of enzyme

Dr. Duncan Clark duncan at genesys.demon.co.uk
Sat Oct 12 03:03:08 EST 1996

In article <Thomas-1110961022330001 at hastingsthomaslc.fas.harvard.edu>,
Thomas <Thomas at hastingslab.harvard.edu> writes
>In article <53k3o9$ct0 at babe.lglobal.com>, jefff at lglobal.com (Jeff F) wrote:
>> Hello!
>> I am wondering if anyone can tell me the definition of one unit of
>> enzyme!
>> Thank you for your time!
>> Jeff F
>> jefff at lglobal.com
>> Toronto
>Unit is a former "unit" to describe the catalytic activity of an enzyme.
>If you buy 1U of an enzyme you get an amount of enzyme that is able to
>convert 1 mikromole of substrate per minute. The actual unit you should
>use is Katal, which is a SI-unit and gives the same information in mole
>per second, so:
>1 U   = 1 mikromol/min
>1 kat = 1 mol/s           (often given as pkat)
>Conversion 1 U = 1.667*10-8 kat

For a restriction enzyme it is always the amount of enzyme necessary to
cut 1ug of substrate DNA (usually lambda but occasionally, pBR322 or
adenovirus2) in 60 minutes in an appropriate buffer at an appropriate
temperature for that enzyme. For say Taq DNA polymerase, one unit is the
amount of enzyme that incoroprates 10nmols of dNTP's into acid insoluble
material per 30 mins at 74C under certain defined assay conditions. So
basically a unit is either already published/defined or it is whatever
you define it to be for your new enzyme. 

My mind's made up. Don't confuse me with the facts!
Duncan Clark
DNAmp Ltd.

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