An EMBOSS application. This calculates the isoelectric point of a protein from its amino acid composition assuming that no electrostatic interactions change the propensity for ionisation. Adjusting the pH of an aqueous protein solution to the point where the numbers of positive and negative charges on the protein are equal brings the protein to its isoelectric point. This is often the point of lowest solubility, presumably because it is the point at which there are fewest intermolecular repulsions, so that the molecules tend to form aggregates. The application can make a plot of the ionisation curve with respect to pH and can write an output file of the data.