[Jazzified]

I was wondering if anyone could direct me to a site in which I can find the molecular weight of alkaline phosphatase (in E. Coli, preferably) in units of g/mol.  I can only find molecular weight in kDa.  Thanks.

[Yggdrasil]

One dalton is equivalent to one gram/mole.

[Jazzified]

Oh okay, thanks!

[Jazzified]

One more question:

Is there any correlation between purity and MW?  If the MW of my experimentally purified alkaline phosphatase is significantly lower than the MW I looked up, does that mean my alkaline phosphatase is impure?  What if my purified alkaline phosphatase has a higher MW than the one I found?  Thanks.

[Yggdrasil]

How are you measuring the MW?  Are you sure that your alkaline phosphatase is from the same source as the value you looked up?  There are two commonly sold alkaline phosphatases, shrimp alkaline phosphatase and calf intestinal alkaline phosphatase.  Since these are two entirely different proteins from two entirely different organisms, they will have different molecular weights.

[Jazzified]

I confirmed with others in my lab that I am measuring correctly.  My total molecular weight for alkaline phosphatase is a little over the literature value.  I am using E. Coli alkaline phosphatase, by the way.  Does this mean that my purified alkaline phosphatase is not that pure?  What are some possible reasons that it is higher than the literature value?

[Yggdrasil]

How contaminants affect the molecular weight of your sample depends on the method that you used to measure the molecular weight.

However, if your sample is just a little bit over the predicted molecular weight, the difference could just be due to experimental error.