1 EU is defined as the amount of enzyme that will yield product formation rate of 1 micromole per minute. So it seems that EU has the units of amount (mass or moles), as it's defined as "the amount of enzyme which..." . But in the class they told us that under certain conditions, 1 EU=the reaction rate. So now - EU has the units of rate... for me it's like you would ask me how old am I and I would answer: 55 mph! How is this transition made from the defenition of "amount" to that of "rate"??? what's the math behind it?

Edited January 22, 201411 yr by assaftolko

I am only aware of using U as a unit of amount and the other one does not make any sense to me. You can estimate enzyme activity from that (by normalizing it against amount) but that is not the definition or usage of U.

Actually I found another refference to the second defenition (which mean U=Vmax if I wasn't clear) here in wikipedia:

 

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

 

Under enzyme activity: "A more practical and commonly used value is enzyme unit (U) = 1 μmolmin⁻¹. 1 U corresponds to 16.67 nanokatals.^[1]"

 

^{Rings any bells?}

1 U of enzyme is the amount of enzyme that will digest 1ug of DNA in 1hr at required/optimum temperature.

1 U of enzyme is the amount of enzyme that will digest 1ug of DNA in 1hr at required/optimum temperature.

 

Assuming that the enzyme in question is a restriction enzyme....that definition doesn't work for other kinds of enzymes.

That's true.