Englund & Lundahl provide a complete set of pK values used in their measurement and calculation of the isoelectric point of the human red cell glucose transporter (Glut 1) (1). The pK values they used in their calculations of the pI of Glut 1 are the averages of the non-microscopic pK values from model compounds and proteins reported by Tanford (1962) in his advances in protein chemistry article (2).