finding GFP's mass

J. Arturo García-Horsman arturo.garcia-horsman at uku.fi
Mon Apr 9 01:55:06 EST 2001


Frederic Langlois wrote:

> Hello.. I'm trying to figure out the different ways to calculate a protein's
> mass for an assignment. In this particular case I want to know the mass of
> the green fluorescent protein (GFP).
>
> 1) The first method I have used is the SDS-PAGE electrophoresis with the low
> range standard markers. I made a standard curve of the standards Rf value (Y
> axis) and the molecular weight (X axis). I extrapolated the GFP's mass using
> it's Rf value.
>
> 2) Then I searched many databanks and found GFP's amino acid sequence. I
> used this equation to find GFP's mass:
>
> mass = [(n1*molecular
> weight1)+(n2*mol.weight2)+...(n20*mol.weight20)]/[(n1+n2+...n20-1)*33g/mol]
>
> where 1=glycin; 2 to 20= all the other amino acids
>       n=the sum of the amino acids of each kind
>       33g/mol=a water molecule's molecular weight (approximately)
>
> I substrated the water molecules that are "lost" when the peptidic bonds are
> made.
>
> I converted the molecular weight in Dalton units...
>
> 3) what are the other methods I can use to find the mass of this protein?
>
> Thanks in advance,
>
> Frederic Langlois

Hello Frederic,

You can just enter your protein sequence in any of the on-line available MW
calculators. For example in:
http://www.expasy.ch/tools/pi_tool.html
you just paste the sequence of your mature protein, or type the SWISS-PROT
and/or TrEMBL entrie for GFP and you will get the theoretical MW, which might be
very similar to the one you determined by SDS-PAGE, if the protein does not
contain any modification (sugars or lipid molecules attached, etc.).

Cheers,

Arturo

_______________________________________________________________

Arturo Garcia-Horsman, Ph.D.
Research Specialist
Department of Pharmacology and Toxicology
University of Kuopio
Canthia, Harjulantie 1 A, 1. krs.
70210 Kuopio, Finland
Tel: +358-017-162422
Fax: +358-017-162424
E-mail: Arturo.Garcia-Horsman at uku.fi





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