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

pI {Peptides} | R Documentation

## 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 = "EMBOSS")

### Arguments

`seq` | An amino-acids sequence
`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"`

### Details

The isoelectric point (pI) is the pH at which the net charge of the protein is equal to 0. It is a variable that affects the solubility of the peptides under certain conditions of pH. When the pH of the solvent is equal to the pI of the protein, it tends to precipitate and lose its biological function.

### Examples

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

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

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

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

    # OTHER SCALES

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

[Package Peptides version 2.4.4 Index]