Isoelectric Point calculations

Dima Klenchin klenchin at macc.wisc.edu
Fri Mar 8 14:09:38 EST 1996

In article <4hmra1$c71$1 at mhadf.production.compuserve.com>,
   Eugene A Kapp <100277.2367 at CompuServe.COM> wrote:
->I have found that the predicted pI calculations from two WWW 
->sites differ by approximately 0.4 for a given protein sequence. 
->Expasy (http://expasy.hcuge.ch/ch2d/pi_tool.html) and the genome 
->sequencing site at (http://genome1.bio.bnl.gov/bbq.html) are 
->therefore using slightly different pKR values.
->Could someone suggest the correct pKR values or add some light to 
->the situation.
->Many thanks.

Very simple. Ignore both. Predicted pI values are meaningless because
they treat all AA as if the protein were random coil. It could be OK for 
small proteins and sometimes is OK with some proteins. Real pI of the folded
protein could be entirely different. So, IMHO, 0.4 unit is not a big deal
of difference. 

- Dima

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