I used proteinase K as a protein digestion step before using a Qiagen AllPrep DNA/RNA extraction kit. I have used it before on WT murine heart and skeletal muscle tissues and got good yield. Today, when I used it on my experimental samples, I got virtually no DNA or RNA.

I added the appropriate amount of ProK to my samples and incubated for 10 mins at 55 degrees as recommended. Then, I spun them down and left the samples on ice while I ate lunch (~45 minutes). This break was the only difference in my protocol today versus my first test run.

I was hoping that icing my samples would inactivate ProK, but I believe that it remained active and digested all of my DNA and RNA.