2mg/ml from a 2U/ml solution????HELP!

[mountain]

hello guys!

I need to prepare a 2 mg/mL DNAase solution. the DNAase stock has a concentration of 2U/ml. how can i make a 2mg/ml from a 2U/ml solution? this is quite hard to figure out :yuck:


hope very much for replies!

thanks for helping!

[Monique]

Look up the specific activity (in U/mg) of the DNase that you have, which company are you using it from? You should look in the catalog under DNase, you will find all the specifications.

[mountain]

hi Monique!

hope that you can help me out!
the Qiagen explicitily says that one mg = 2500 Kunitz units. but still my brain doesn't "work" :cry:
can you please show me how you would make a 2mg/ml from a 2U/ml if 1mg=2500 Kunitz units? by the way what does Kunitz units mean?

hope so much for advices!

[iansmith]

Kunitz units is a unit used in biochemistry to describe the concentration or activity of the enzyme ribonuclease, which attacks ribonucleic acid (RNA). Ordinarily RNA absorbs ultraviolet light, so the activity of ribonuclease can be measured by observing the decrease of this absorption. One kunitz is the concentration of the enzyme causing a decrease of 100% in the absorption in a time of one minute, the measurement being made under certain standard laboratory conditions. The unit's name recognizes the Russian-American biochemist M. Kunitz, who proposed the standard test in 1946.

but it is not the same as U

enzyme unit (U or EU)
a unit used by biochemists to measure the activity of enzymes, which are proteins produced by living cells to cause or facilitate necessary chemical reactions within the cell. One enzyme unit is the quantity of enzyme needed to cause a reaction to process 1 micromole of substance per minute under specified conditions. Thus, one enzyme unit has a catalytic activity of 1/60 microkatal (µkt) or 16.667 nanokatals (nkt).

http://www.unc.edu/~rowlett/units/dictK.html

Enzyme unit can also change from manufacturor. You may need to search the supplier website as alot of information is available in their tech. bulletin that are not available in their catalogues. For example fermatas says that 1 Kunitz unit of some of their enzyme is equal to 50 U.

[Moonbear]

Don't waste your time hunting through catalogs and websites. Call the manufacturer's tech support directly and ask them. Have the catalog # and lot # on hand. Depending on the size of the company, the person answering the phone may or may not be able to answer your question, but let them do the legwork of finding the person there who knows the answer.

However, units refers to the actual activity of the DNase, so you might be better off using it in U/ml than mg/ml to be more consistent from reaction to reaction. Iansmith or Monique, you two work with these methods more often than I do...do you have an opinion on whether it's better to work with concentrations in U/ml than mg/ml for an enzyme such as this? Of course, the first time, mountain will need to know the conversion just to get close to what has been used previously.

[iansmith]

We usually use the U/uL for enzyme in solution and g/mL for freeze dry enzyme.