Isoelectric Points of Two Molecular Forms of Human Urinary Urokinase determined by Density-gradient Isoelectric Focusing and Isotachoelectrophoresis

抄録

The isoelectric points (pI's) of MW 55000 form (H-UK) and MW 36000 form (L-UK) of human urinary urokinase (UK) were determined by sucrose density-gradient isoelectric focusing. These values were compared with the pI's which had been estimated previously by isotachoelectrophoresis. All five subforms fractionated from H- or L-UK by isoelectric focusing were confirmed to exhibit plasminogen activator activity and to be homogeneous in terms of molecular weight. The pI's evaluated by isoelectric focusing were in accordance with those by isotachoelectrophoresis, for all five subforms of H-UK (pI 8.70, 8.86, 9.05, 9.20 and 9.44) and for three subforms of L-UK (pI 7.54, 8.26 and 8.84). The pI's of the two most alkaline subforms of L-UK (pI 9.17 and 9.43) were underestimated by up to 0.3 pH unit by isoelectric focusing as compared with the values obtained by isotachoelectrophoresis (pI 9.4 and 9.7, respectively). Thus, the differences between the pI's determined by the two kinds of electrophoresis were slight and restricted to two of the ten subforms.