It is the same, Units = International Units, transformation of 1 micromol/min

Other unit is called Katal= moles/seg. Too high

yes, I agree with Fransisco. U and IU interchangeably used in research, however, when IU is used, it is presumed in most cases that there is a well known activity unit definition where as when it is simply used U, it may infer the method is customized. both can be used..

Thankyou for the clarifications.

Yes, I agree with both of them, 1 U or IU is defined as the enzyme quantity that liberates 1 microgram or micromole of product per ml of the reaction mixture per minute.

For IU and kat, the units are predeined. If you want to use others units (mol, mmol, µmol,...  or g, mg ... per seg, min or h, etc.), write U and give the definition.

The enzymatic activity unit is defined by the IUBMB (International Union of Biochemistry and Molecular Biology) in 1981. For more details, you can read the article.of Cornish-Bowden A. 

http://www.sciencedirect.com/science/article/pii/S221302091400007X

Solano sir, isn't it like....

U is the international unit of enzyme activity.It is 1 micromole of substrate or product transformed/min.

But IU is international units which represents the amount of biological agents(vitamins,vaccines) in different preparations producing the same biological effect.

Hi All. " full disclosure" I am a biochemist by training and I absolutely HATE this IU and U  labels on drugs.

They make sense to clinicians because these units have ben optimized for their work in the OR and ICU.

But getting a clinical vial of a drug and trying to make sense of the marking with respect to concentration and efficacy is impossible unless you know what assay (s) were run on it.

I agree with Francisco Solano , Most of the enzyme supplier uses the term as IU, amount of enzyme convert I µ mol substrate per min. Estimation and calculation Katal as such is difficult ( within one second ) and also it is a very high unit ( moles/second). Otherwise U and UI is same

When using International units it is necessary that the measurement be done under specified conditions such as 25o C.

You can use any units as long as it is defined.  I also know people using u/mg of protein (Specific activity etc).

the same and you can use any one

The enzyme unit (U) is a unit for the amount of a particular enzyme. One U is defined as the amount of the enzyme that produces a certain amount of enzymatic activity, that is, the amount that catalyzes the conversion of 1 micro mole of substrate per minute. The enzyme unit (U) should not be confused with the International Unit (IU).

In pharmacology, the international unit is a unit of measurement for the amount of a substance; the mass or volume that constitutes one international unit varies based on which substance is being measured, and the variance is based on the biological activity or effect, for the purpose of easier comparison across substances. International units are used to quantify vitamins, hormones, some medications, vaccines, blood products, and similar biologically active substances.

So Mohammad Mohkami, is there any differences between the two (IU and U)?You stated there do not confuse between those two, which means there are not the same unit. I need to prepare a Penicillin G sodium antibiotic at concentration of 1.5 IU, but at the bottle it is written there 1670 U is equivalent with 1mg. Can you help me answer this? Thank you

This link can helps you

http://www.physiologyweb.com/calculators/units_per_volume_solution_concentration_calculator.html

U is defined as the amount of the enzyme that produces a certain amount of enzymatic activity, that is, the amount that catalyzes the conversion of 1 micro-mole of substrate per minute. The conditions also have to be specified: one usually takes a temperature of 25°C. and the pH value and substrate concentration that yield the maximal substrate conversion rate.

Please help me in this regard

1 mmol units equals to how much IU/L?

Can somebody help me, please?

I am working with GSTP1 protein. I saw some papers that the concentrations are U/mL, but I bought a protein that the concentration is mg/mL. Is it possible convert this? How can I do this?

Thank you

International Units per mL or (I.U/mL) is the same as (U/mL) which their unit is (μmol /min)

The enzyme unit (U), or international unit for enzyme (IU) is a unit of enzyme's catalytic activity. 1 U (μmol/min) is defined as the amount of the enzyme that catalyzes the conversion of 1 micromole of substrate per minute under the specified conditions of the assay method.

Enzyme Activity(μmol/min ml) or (U/ml) = (Consumed Substrate) ×Total Reaction Volume / (Reaction time (min)) × (Enzyme volume(ml))

Dear Mohiuddin Yatoo,

1 mmol/mL= 10^6 μmol/L

Please how can i convert enzyme activity in FPU/mL to U/mL