Experimental Molecular Weight higher than Literature Value

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Homework Statement

I just purified alkaline phosphatase, and my calculated molecular weight is 100000 g/mol, while literature value is 89000 g/mol. According to how others in my lab did calculations, my calculations are performed correctly, so I am left to explain why my purification is higher than expected.

Homework Equations

N/A

The Attempt at a Solution

I was thinking that since alkaline phosphatase can be inhibited by EDTA, my "purified" enzyme contains some EDTA, making the molecular weight higher.

 

[chemisttree]

Did you purify it by gel electrophoresis? What was the supporting electrolyte? Did you completely dialyze your product?

 

[epenguin]

You do not give any indication of what method used for getting the MW so what can anyone say?