For example, each of the buffers used for gene cloning contains DTT (dithiothretol). The restriction digestion buffers all contain DTT.
DTT is indeed included in the buffer formulation, but it has been found now that it is not necessary for restriction enzyme activity. Also, on repeated thawing and freezing, BSA and DTT together form white precipitate which is not desirable.
DTT commonly is used as redox reagent to prevent formation of disulfide bonds in cysteine-containing proteins. Such proteins require proper formation or absence disulfide bonds for exhibiting of specific activity. DTT helps to keep cysteine-containing proteins in active state.However, if protein doesn't contain cysteins, there is no need to use DTT for its activity.
Almost all digestion buffers have DTT which reduces disulfides, and its a known fact now that they have no role at all for the activity of restriction enzymes and just preventing the cysteines residues on different proteins or you can use the word enzymes here to form the inter or intra cross linking which actually and ultimately disrupt the structure and activity of restriction enzymes and of course it is not suitable for the cloning protocols. Only 1 mM usually is added in various restriction digestion buffers...
DTT (Dithiothreitol) is a very useful reducing Agent for disulfide bonds. With this it stabilizes enzyms and proteins which posses free sulhydryl groups.
DTT breaks di-sulfid bond and loosen the secondary structure of RNA and helps in initiation of transcription so it must for cDNA synthesis.
If your Enzyme posses free sulfhydryl groups at the active site, the addition of DTT is useful in the extraction buffer.
You can try and see if the addition of DTT at a final concentration of 1 to 2 mM in the enzyme assay has an effect on the enzyme activity.
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