Peptides (version 1.1.2)

pI: Compute the isoelectic point (pI) of a protein sequence

Description

The isoelectric point (pI), is the pH at which a particular molecule or surface carries no net electrical charge.

Usage

pI(seq,pKscale)

Arguments

seq

amino acid sequence string in upper case

pKscale

a character string specifying the pK scale to be used; must be one of "Bjellqvist", "EMBOSS", "Murray", "Sillero", "Solomon", "Stryer", "Lehninger", "Dawson" or "Rodwell"

Examples

# COMPARED TO ExPASy ProtParam
# http://web.expasy.org/cgi-bin/protparam/protparam
# SEQUENCE: QWGRRCCGWGPGRRYCVRWC
# Theoretical pI: 9.88

pI("QWGRRCCGWGPGRRYCVRWC","Bjellqvist")
# [1] 9.881

# COMPARED TO EMBOSS PEPSTATS
# http://emboss.bioinformatics.nl/cgi-bin/emboss/pepstats
# SEQUENCE: QWGRRCCGWGPGRRYCVRWC
# Isoelectric Point = 9.7158

pI("QWGRRCCGWGPGRRYCVRWC","EMBOSS")
# [1] 9.716

# OTHER SCALES

pI("QWGRRCCGWGPGRRYCVRWC","Murray")
# [1] 9.818
pI("QWGRRCCGWGPGRRYCVRWC","Sillero")
# [1] 9.891
pI("QWGRRCCGWGPGRRYCVRWC","Solomon")
# [1] 9.582
pI("QWGRRCCGWGPGRRYCVRWC","Stryer")
# [1] 9.623
pI("QWGRRCCGWGPGRRYCVRWC","Lehninger")
# [1] 9.931
pI("QWGRRCCGWGPGRRYCVRWC","Dawson")
# [1] 9.568
pI("QWGRRCCGWGPGRRYCVRWC","Rodwell")
# [1] 9.718