Experimental Molecular Weight higher than Literature Value

In summary, the conversation discusses a discrepancy in the calculated molecular weight of purified alkaline phosphatase. The speaker suggests that the higher than expected value may be due to the presence of EDTA. They also ask for more information about the purification method used.
  • #1
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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.
 
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  • #2
Did you purify it by gel electrophoresis? What was the supporting electrolyte? Did you completely dialyze your product?
 
  • #3
You do not give any indication of what method used for getting the MW so what can anyone say?
 

1. What factors can contribute to an experimental molecular weight being higher than the literature value?

There are several potential factors that can lead to an experimental molecular weight being higher than the literature value. These include impurities or contaminants in the sample, errors in the experimental procedure, and differences in the conditions under which the experiment was conducted compared to the conditions used to determine the literature value.

2. How can impurities affect the measured molecular weight?

Impurities in a sample can contribute to a higher measured molecular weight by adding additional mass to the sample. This can occur if the impurities have a higher molecular weight than the desired molecule or if they bind to the desired molecule, increasing its overall mass.

3. Can experimental errors also lead to a higher molecular weight?

Yes, experimental errors such as incorrect calculations or imprecise measurements can contribute to a higher measured molecular weight. It is important to carefully control and document all experimental procedures to minimize the potential for errors.

4. Are there any other factors that can result in a higher experimental molecular weight?

In addition to impurities and experimental errors, differences in the conditions under which the experiment was conducted compared to the conditions used to determine the literature value can also lead to a higher measured molecular weight. This can include variations in temperature, pressure, or concentration of reagents.

5. How can discrepancies between experimental and literature molecular weights be resolved?

If there is a significant difference between the experimental and literature molecular weights, it is important to carefully review the experimental procedure and data to identify potential sources of error. Repeat experiments may also be necessary to confirm the results and rule out any potential errors. Additionally, comparing the results to other literature values or consulting with other scientists in the field can help to resolve any discrepancies.

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