ProteinPropertiesCalculator.php
Protein properties : net charge, isoelectric point, hydropathy Freely inspired by BioPHP's project biophp.org Created 9 October 2026 Last modified 9 October 2026
Table of Contents
Classes
- ProteinPropertiesCalculator
- The net charge is the sum of the partial charges of the groups that carry one - the N-terminus, Lys, Arg and His (positive), the C-terminus, Asp, Glu, Cys and Tyr (negative) - each given by the Henderson-Hasselbalch equation, 1 / (1 + 10^(pH - pK)) for a base and 1 / (1 + 10^(pK - pH)) for an acid. The pK values are the caller's (bioapi serves three sets : EMBOSS, DTASelect, Solomon) : a protein has no isoelectric point of its own, only one for a given set. The isoelectric point is the pH where that charge is zero, found by bisection - the charge falls as the pH rises, always, so it crosses zero once. The terminal groups are the ones of the set, not residue-specific ones.