Courtni E. Allen and Michael P. Schmitt. Utilization of Host Iron Sources by Corynebacterium diphtheriae: Multiple Hemoglobin-Binding Proteins Are Essential for the Use of Iron from the Hemoglobin-Haptoglobin Complex. J. Bacteriol. February 2015 vol. 197 no. 3 553-562. doi: 10.1128/JB.02413-14

...Cell debris was removed by centrifugation at 12,000 × g at 4°C, and the supernatant fraction containing the soluble protein was purified on Strep-Tactin columns (Neuromics) for Strep-tagged constructs...