ENHANCED STABILITY OF 2 MODEL PROTEINS IN AN AGITATED SOLUTION ENVIRONMENT USING POLOXAMER-407

To enhance the physical stability of two model proteins during solutio n agitation, we investigated the interaction of the nonionic surfactan t poloxamer 407 (Pluronic(R) F-127) with each protein. Vigorous agitat ion of aqueous solutions of interleukin-2 and urease which contained n o poloxamer 407 and were maintained at 4-degrees-C resulted in a great er than 50% loss in the biological activity at 12 and 24 hours, respec tively. Similar aqueous solutions which were maintained at 4-degrees-C and contained either urease or interleukin-2 and poloxamer 407 at a c oncentration of 10% w/w and 0.5% w/w, respectively lost negligible bio logical activity when left undisturbed for 96 hours. Moreover, when aq ueous solutions of urease and interleukin-2 which contained poloxamer 407 at a concentration of 10% w/w and 0.5% w/w, respectively were main tained at 4-degrees-C and subjected to agitation for 96 hours, no sign ificant loss in the biological activity was observed for either protei n. In addition, urease was observed to have increased enzymatic activi ty at early time points regardless of the hydrodynamic solution condit ions and poloxamer 407 concentrations evaluated. In contrast, a neglig ible enhancement in the biological activity of interleukin-2 was obser ved when aqueous solutions of the protein were exposed to similar hydr odynamic conditions employed for urease solutions, but different polox amer concentrations (0% w/w vs. 0.5% w/w). Results of molar ellipticit y, [theta], versus wavelength, lambda profiles using CD spectropolarim etry on individual aqueous solutions of both proteins containing 2% w/ w poloxamer 407 were in close agreement to spectrum obtained with each protein in pH = 7 phosphate buffer (PB). However, values of [theta] o bserved for both proteins in a solution which contained poloxamer 407 relative to values of [theta] obtained for each protein in pH = 7 PB w ere inversely related to the values of [theta] observed for each prote in in an aqueous solution which contained 0.5% w/w sodium dodecyl sulf ate. Based on our studies using circular dichroism, it was concluded t hat incubation of both interleukin-2 and urease with poloxamer 407 did not result in significant changes in the secondary structure Of eithe r model protein when compared to the CD spectrum obtained for each pro tein in a stable pH = 7 PB.