In this short exercise, students prepare their purified lysozyme from the previous exercise for running on an SDS-PAGE gel. The electrophoresis system I use is Bio-Rad's Mini-Protean II. Since lysozyme is such a small protein, a high monomer concentration (15%; 2.7% crosslinked) works best. I have used Sigma's Dalton Mark VII low-molecular weight standards. The last time I did this (spring of 2001), students precipitated 0.25 mL of their purified lysozyme with 0.75 mL of acetone, then dissolved the precipitate with 0.5 mL of sample buffer in a boiling water bath. They applied 15 microliters of this sample to a 0.75 mm gel set up with ten wells. Then I ran, fixed, stained, destained, and dried the gels and gave each of them their respective lane.

I also ran a gel with the low molecular weight standards in one lane and a sample of lysozyme in an adjacent lane and, after staining the gel, made photocopies for the students to use to determine lysozyme's molecular weight using a semilog plot.

For some reason, the students' lanes showed no stain where lysozyme should run, but all had some traces of other proteins, especially albumin. Probably their amounts of lysozyme were simply too small, since a gel with authentic pure lysozyme stained well. I'll have to tweak conditions so they can see their product.

Revised 9/12/07