AGGREGATION OF RHDNASE OCCURRED DURING THE COMPRESSION OF KBR PELLETSUSED FOR FTIR SPECTROSCOPY

Purpose. To determine if a protein changes when it is compressed into a KBr pellet for FTIR spectroscopy measurement in the solid state, usi ng recombinant human deoxyribonuclease I (rhDNase) as an example. Meth ods. Lyophilized rhDNase with KBr compressed at different pressures we re analyzed by FTIR spectroscopy, size exclusion HPLC and enzymatic ac tivity assay. Different protein/KBr weight ratios and residual water c ontents were studied for their possible effects on aggregation. Result s. Depending on the pressure, a loss of enzymatic activity accompanied by an increase in soluble high molecular weight aggregates of the pro tein (up to similar to 15%) was demonstrated. Aggregation was reduced to less than 5% by a suitable dilution of the protein in KBr (1 in 100 0). In contrast, water content variability (1-11 wt. %) did not affect aggregation. Conclusions. The findings emphasize the importance to ex amine for protein integrity when using the KBr method for FTIR sample preparation. Protein aggregation may be minimized by optimizing the sa mple preparation condition such as changing the protein/KBr weight rat io.