Immobilized pH gradient focusing of alkaline proteins: analysis of the isoform composition of purified human non-secretory ribonucleases from kidney, liver and spleen.

Previous studies on the isoform composition of human ribonucleases (RNAases) have resulted in confusing and inconsistent results, presumably due to methodological problems in electrofocusing of alkaline proteins. In the present study, immobilized pH gradient (IPG) carrier ampholyte (CA) isoelectric focusing (IEF) and conventional CA-IEF have been evaluated for the analysis of the isoforms of human non-secretory RNAases purified from kidney, liver and spleen. CA-IEF proved unsuitable since the alkaline RNAase isoforms migrated into the cathode. IPG-CA-IEF, however, resolved the RNAase isoforms and marker proteins in the basic region of the gel matrix. The three RNAases had comparable isoform profiles, each with two protein bands with approximate pI values of 10.3 and 10.4. Western blotting showed that the two protein bands of each RNAase were immunoreactive (with polyclonal antibodies that recognize RNAase), indicating that the protein bands are RNAase isoforms. The present results provide reliable pI data on human RNAase isoforms and suggest that IPG-CA-IEF should be a suitable technique for analysing the isoforms of other alkaline proteins.