🚀 go-pugleaf

In article <9107111900.AA24364@genbank.bio.net> UOG10004@VM.UOGUELPH.CA (Gopal Thinakaran) writes:

      Does anyone know of a program that calculates the isoelectric point
      of proteins given the amino acid sequence?  We have an IBM-PC but I
      could get access to Mac or Unix.  I want to verify if I have
      immunoprecipitated the right protein.  I also want to check if a
      dimer band is due to different phosphorylated forms of the same
      protein or a contaminating protein.  I am considering in vitro
      transcription/translation of the cDNA as my last option.

A program to do this calculation on the assuption that all groups titrate
at their standard values (see Nozaki & Tanford, Meth. Enzymol., 130,
715 (1967) for these values) would be straightforward.  However, this
assumption is dangerous since many proteins have groups with
significantly shifted pKa's.  For example, lysozyme has a Glu with
pKa ~ 6 and myoglobin has three histidines that protonate only
upon acid induced unfolding.  I co-authored a recent paper on attempts
to do calculations of such shifts (Bashford & Karplus, Biochemistry, 29,
10224 (1990)).  Although the results were encouraging, they are not
good enough to predict isoelectric points reliably.

Don Bashford
The Scripps Research Institute
bashford@scripps.edu