Isoelectric points of two molecular forms of human urinary urokinase determined by density-gradient isoelectric focusing and isotachoelectrophoresis.

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Abstract
The isoelectric points (pI) of MW 55,000 form (H-UK) and MW 36,000 form (L-UK) of human urinary urokinase (UK) were determined by sucrose density-gradient isoelectric focusing. These values were compared with the pI which had been estimated previously by isotachoelectrophoresis. All 5 subforms fractionated from H- or L-UK by isoelectric focusing were confirmed to exhibit plasminogen activator activity and to be homogeneous in terms of MW. The pI evaluated by isoelectric focusing were in accordance with those by isotachoelectrophoresis, for all 5 subforms of H-UK (pI 8.70, 8.86, 9.05 9.20 and 9.44) and for 3 subforms of L-UK (pI 7.54, 8.26 and 8.84). The pI of the 2 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 determined by the 2 kinds of electrophoresis was slight and restricted to 2 of the 10 subforms.