Stability of urokinase in solutions containing sodium bisulfite

The stabilities of urokinase (UK) in aqueous solution were investigated at pH 5.0-8.0 in the presence (1.0-3.0 x 10(-3) M) and absence of sodium bisulfite (SBS) both under scattered light (1000 lux) and in the dark using the fluorogenic substrate method. Increasing concentrations of SBS tended to increase the inactivation of UK. In the presence of SBS, with the increase in the pH value, UK gained in stability in the pH range of 5.0-8.0. The stability of UK in the presence of SBS in the dark was larger than that under scattered light, especially at pH 5.0. Therefore, it was suggested that the difference in the residual activities of UK between under light and in the dark was due to free radicals formed during the autooxidation of bisulfite under scattered light. UK was stabilized by glucose in the presence of SBS both under scattered light and in the dark. One reason for this phenomenon was postulated to be the formation of inactive bisulfite-glucose addition compound. The degradation products of UK during storage in a solution containing SBS were investigated by sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis. UK was revealed to be split into M.W. 36000 form and M.W. 20000 form by SBS.