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one unit of enzyme

Hernan Espinoza espinoza at cgl.ucsf.edu
Sat Oct 12 13:40:18 EST 1996

jefff at lglobal.com (Jeff F) writes:

>I am wondering if anyone can tell me the definition of one unit of

	There is no standard unit for all enzymes.   A unit is just
a number for measuring the _activity_ of an enzyme preparation.  Usually,
the form is something like : 1 unit = the amount of the enzyme preparation 
needed to convert X amount of substrate to product in a given amount of
time under a given set of conditions.  As you can see, it's pretty flexible.

An example :  Restriction endonucleases from NEB use 1 unit = the
amount of enzyme needed to convert 1 microgram of uncut DNA to
cut DNA in 1 hour at 37C

HOWEVER, it could just as easily be 1 unit = the amount of enzyme needed
to convert 1 mmol of uncut target oligo to product in 15 minutes at 37C

OR,  1 unit = the amount of enzyme needed to covert 1 microlitre of my
pUC19 plasmid preparation into fully digested product in 2 hours at RT

The point is the unit definition is dependent on the enzyme in question,
the method used to measure activity, and (to a certain extent) the whim
of the investigator.   There are no hard and fast rules, but there are
conventions for certain enzymes to facilitate comparison between
investigators.   In addition, your collegues are more likely to respect unit
definitions like the first two rather than the last...

	Hope this helped.   -Hernan

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