I want to know exactly what is the unit of antioxidant assay in seeds. I find some different unit in articles such as U/ mg prot or U/ mg FW or U/ mg prot in one minute. Please refer me to some articles.
Unit, Antioxidant, seed
Hello,
It is depended to the assay method. In indirect methods (measurement of enzyme activity using substrate), enzyme units are expressed. Unit can be expressed per mg protein or mg weight (dry or wet). Both can be correct, but protein is preferred. If based protein, dilution does not interfere the results, thus this way is more frequently used. Based on weight needs precise dilution and weight measurement. About the time, in some measurement methods the enzyme activity is expressed over time. For instance, if the enzyme catalyze a reaction causing reduction or elevation of optical density over time, it is better to express its activity based on time.
For enzyme activity the most suitable Unit U/mg total protein. This you can determine by your assay principle - wether you are quantifying the rate of substrate consumption or product appearance.
Dear Hamed, this is a good question and need to details for explanation but briefly:
For activity expression we use two types of units for two types of samples.
when you encounter to a liquid sample contains a specific enzyme, you can use international unit per volume of the sample. e.g IU/mL or IU/L. you know international unit is well defined for each enzymes, micromol of substrate or microml of product which is consume or produce during minute by the enzyme.
when you encounter to an activity which is dependent to more than one enzyme in liquid sample, you have to use arbitrarily unit (but not international unit), and finally express unit per volume e.g U/mL or U/L.
when you encounter to a solid sample contains a specific enzyme, you can use international unit per weight of the sample. e.g IU/g tissue or IU/mg tissue or mg sample such as mg plant powder and so on. But you know solid sample is not homogeneous as liquid sample so you need a molecular correction for the result. a good manner is determining protein content of solid biological sample and express the enzyme activity based on e,g IU/mg protein tissue or sample.
when you encounter to a solid sample contains more than one enzyme, you have to use arbitrarily unit per weight of the sample. e.g U/g tissue or U/mg tissue or mg sample such as mg plant powder and so on. But you know solid sample is not homogeneous as liquid sample so you need a molecular correction for the result. a good manner is determining protein content of solid biological sample and express the enzyme activity based on e,g U/mg protein tissue or sample.
So finally for total antioxidant activity in a solid sample such as plant powder, rat liver and so on, you are one way, express the antioxidant activity based on unit but not international unit, and express it based on weight but not volume and better based on molecular scale such as mg or gram protein or finally Unit/mg tissue protein.
regards
mehdi
Hello Hamed Farhadi,
You will use the unit of different antioxidant enzymes, that depends on you. The unit may be U/g fresh weight (FW), or U/mg FW or U/ mg protein, U/ml, or U/L, anyone is okay. Sometimes, the unit depends on the result (enzymes amount i.e, volume) or unit density per ml liquid sample or mg protein or g protein, that is convenient to express.
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Enzyme activity of the most suitable Unit of total protein is U/mg. It can be determine by the assay principle - whether it can quantify the rate of substrate consumption or product appearance.
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