Question about concentrations...

William Tivol tivol at
Fri Nov 8 14:00:34 EST 1996

Yates (yates at wrote:

: What does "5U/ml" mean when it indicates insulin concentration,
: and what do you need to convert it to 5M ?

	5U means 5 units of activity.  In order to convert, you need to find
out what the activity of a particular number of molecules is.  The activity
is usually stated in terms of a quantity of product produced from substrate
in a given time at standard conditions, and these will vary for different
enzymes (or vitamins or hormones, etc.).  You will have to look up the defi-
nition of a unit of activity for insulin and the activity for pure insulin--
which may vary for bovine vs human, etc.  Alternatively, you could measure
the activity and amount of your prep to determine the conversion factor.
	All this is somewhat complicated, and it arises from the ease of
measuring the activity of a substance--often not purified when the unit was
defined--versus quantitating the number of molecules.  In the case of insulin,
the clinically relevant number for treatment is the activity, and since this
can differ depending on the source and method of purification, it is better
to prescribe x units than y mmol.
				Bill Tivol

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