Effect of shear on human insulin in zinc suspension

Human insulin in zinc suspension was used as a model protein to test the effect of shear on the settling rate of proteins, a possible inference for protein denaturation. The rate of settling was determined directly in a spectrophotometer. Shear effects are important in retaining the activity of proteins and are present in bubble, foam, and droplet protein fractionation processes. A simple test, such as that conducted here, may even be useful for monitoring changes in protein structure caused by commercial shipping of the protein. The settling rate for insulin was continuously monitored in the original bottle by spectrophotometric absorbance changes as a function of time. A settling curve was determined following each shear experiment, which included shaking the "worked" insulin solution in a vortex mixer for different lengths of time. It was determined, when comparing long shaking times with short ones, that the initial settling rate was less for the long-term shaking of the insulin samples and greater for the short-term shaking. The secondary effects of light and heat, along with shaking, apparently did not produce differences from shaking alone.