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Calculation - (Oct/31/2006 )


I was going over a practice exam and came across this question-I have NO idea how to do this-theres quite a few q's like this-so is it possible for someone to explain how to work it out so I can try the other ones?

One unit of enzyme is defined as the amount of enzyme which catalyses the hydrolysis of 1 µmol of substrate per minute.
How many units of enzyme are there are in 10 mL of enzyme solution if 0.1 mL hydrolyses 400 nmol in 10 minutes?


Thanks in advance


to start with, u have to convert nmol substrate to µmol per minute as what is stated in the definition should end with 0.04µmol/min
but this is the amount in 0.1ml not in 10ml, do your calculation and you are supposed to end with 4 units...



No, i think 4 units is not the right answer. 0.4umol/mL is not an "amount", right?

It's not so complicated. First yes, use same units for all calculations (i. e. umol/mL). Begin calculating how much substrate is hydrolizing per minute. Then calculate how much enzyme needs for hydrolize that amount of substrate. Now consider that that amount of enzyme is in 0.1 mL of reaction, so calculate how much there'll be on 10 mL. And that's it. Only pencil and paper you need.



Sorry, i mean 0.04 umol/min is not an "amount"


I agree it's 4 units


Hi there

Thanks for that--I did a few more and got them right-yay!

but then I came across this one:

One unit of enzyme is defined as the amount of enzyme which catalyses the hydrolysis of 1 μmol of substrate per min. Calculate the volume (in mL) of the solution of alkaline phosphatase which contains 5 units of the enzyme if 0.2 mL of it hydrolyses 200 nmol of substrate in 20 mins.
-1.0 x 105

How do I do this if I have 'units' what am i suppose to convert??

Thanks in advance


the key here is just to know that 5 enzyme units mean 5μmol to convert 1μmol of substrate (PLZ..correct me if this is wrong unsure.gif )

-it's the same, convert nmol to μmols
-calculate how many μmol per 1 minute
-you should end with 0.01μmol /min
-so 0.2ml solution contains 0.01μmol /min, but if you have 5μmol /min ....what volume could be the right one?

i got 100ml.... smile.gif