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GST enzyme unit

GST enzyme unit - Protein Science

GST enzyme unit - Post Questions and Discuss Protein Structure and Function, Protein Localization etc.. Please do not post Proteomic questions here, there is a Proteomic Forum below.


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Old 11-21-2008, 02:57 PM
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Default GST enzyme unit



How can i change the GST activity value from IU/L to nmol/min/ml.
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Old 11-21-2008, 03:10 PM
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Default Re: GST enzyme unit

hmm will check this and get back to you.
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Old 11-22-2008, 01:29 PM
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Default Re: GST enzyme unit

thanks
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Old 11-26-2008, 04:51 PM
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Default Re: GST enzyme unit

i am waiting for your reply if u can help me i will be very much thankful.
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Old 12-24-2008, 11:45 AM
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Default Re: GST enzyme unit

Hello,

1 IU is 1umol/min which is equal to 1000 nmol/min which is equal to 1000 mIU/min (mIU = milli-international-units)

Therefore 1 IU/L is 1umol/min/L

which is equal to 1000 nmol/min/1000 ml

which is equal to 1 nmol/min/ml !!

That is, if you enzyme preparation has an activity of 1 IU/L, meaning that 1 L will produce a rate of 1umol/min, it also has an activity of 1nmol/min/ml, meaning that 1 ml will produce a rate of 1 nmol/min.

The units are equivalent, and are just alternative ways of saying the same thing, provided that the assay conditions are identical in both cases.


Note that if you require a specific activity measurement you will need a protein concentration and convert to (for example) umol/min/mg.

A specific activity of 1 IU/mg means that 1 mg of enzyme will produce an initial rate of 1 umol/min under specified assay conditions (temperature, pH, etc). The assay conditions should always be specified. The specific activity at 37 degrees C would be expected to be higher than that at 25 degrees C, for example,

Good luck,

tgd
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  #6  
Old 02-03-2009, 07:55 PM
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Default Re: GST enzyme unit

Hi tgd,

Would you mind showing a quick calculation of determing the specific activity of something..let's say conveting something from 90pmol/min to nmol/min/mg based on any protein concentration (let's say in uM)?

thanks
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Old 02-04-2009, 10:46 AM
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Default Re: GST enzyme unit

Hello,

Let's say that 25 ul of the enzyme preparation (pure or not pure) gives an initial rate of 90 pmol/min under defined assay conditions (constant pH, Temp, etc).

Let's also assume that the protein concentration of the enzyme preparation, which you have determined separately by the Lowry method or the Markwell method or the like, is 10 mg/ml (10 milligrams per ml).

We can then write:

1. Activity of preparation = 90 pmol/min/25 ul.

2. As 25 ul (25 microlitres) is equivalent to 250 ug (250 micrograms) [from the protein concentration measurement]

3. Specific Activity of Preparation = 90 pmol/min/ 250 ug

or, converting to 'per milligram' basis.

4. Specific Activity of Preparation = 360 pmol/min/mg.

Twomportant assumptions of such calculations, which you probably know, are:

(i) The velocity versus (amount of enzyme added) plot should be linear and through the origin.

If, say, 25 ul gives a rate of 90 pmol/min then 50 ul should give a rate of 180 pmol/min and 12.5 ul should give a rate of 45 pmol/min., etc. Furthermore, if there is a 'blank' rate, this must be subtracted.

(ii) You are measuring the *initial* rate.

Two great references:

1. I. H. Segel "Biochemical Calculations (3rd Edition)

2. Enzymes by Malcolm Dixon, E.C Webb, K.F. Tipton & C.J.R Thorne (3rd Edn, 1979). (In particular the first couple of chapters)

I hope this is of help, and is what you want.

If not you can let me know, perhaps by posting a specific example? In my view, specific activity measurements are important. 'Specific', in the sense used, means express on a *per weight* basis.


tgd
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  #8  
Old 09-27-2009, 03:17 AM
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Default Re: GST enzyme unit

My question is that how can i change the GST activity value from IU/L to nmol/min/ml.
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  #9  
Old 09-27-2009, 10:50 PM
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Default Re: GST enzyme unit

Hello,

An IU (International Unit) is 1umol/min (at defined pH, temp, etc), or 1000 nmol/min.

1 IU/L is equivalent to 1 umol/min/L or 1000 nmol/min/L, or 1000 nmol/min / 1000ml

1 IU/L is therefore also equivalent to 1 nmol/min/ml !!

If, say your enzyme is present at a concentration, determined by enzyme assay,
of x IU/L is is also present at a concentration of x nmol/min/ml.

Note that this is not the same as specific activity, which will require an estimation of
the protein concentration, and will be expresed in units of (say) nmol/min/mg or IU/mg.

(umol = micromole, mg = milligram)

Good luck

tgd
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