Ultrasonic energy as a new tool for fast isotopic 18O labeling of proteins for mass spectrometry-based techniques: Preliminary results

Preliminary results regarding fast isotopic labeling of proteins with 18O in conjunction with matrix assisted laser desorption ionization time of flight mass spectrometry technique are presented. Similar 16O/18O isotopic labeling ratios were found for the overnight procedure (12 h) and the new fast ultrasonic one (30 min) for the BSA, ovalbumin and α-lactalbumin proteins. The procedure, however, failed to promote double 18O isotopic labeling for the proteins, ovalbumin and α-lactalbumin. Two different sonication frequencies, 35 and 130 kHz, were studied at two different sonication times of 15 and 30 min, being best results obtained with the procedure at 130 kHz of sonication frequency and 30 min of sonication time. For comparative purposes the overnight isotopic 18O labeling procedure was done. In addition, the new fast isotopic labeling procedure was also studied without ultrasonication, in a water bath at 60 °C.