PURIFICATION AND CHARACTERIZATION OF THE ACID-STABLE PROTEINACEOUS INHIBITOR OF POTATO-TUBER INVERTASE BY NONIDEAL SIZE-EXCLUSION CHROMATOGRAPHY

The objective of this research was to purify the protein that binds an d reduces the activity of potato (Solanum tuberosum L.) tuber acid inv ertase. Our attempt to isolate invertase inhibitor from potatoes (cv. Katahdin) using previously published procedures resulted in the inhibi tor co-purifying with several other proteins without inhibitor functio n, of similar weight but different pi values. These impurities were ob scured on SDS-PAGE discontinuous polyacrylamide gels since after the f irst purification step all the proteins had molecular weights ranging from 17 to 18 kDa. Using a glycerol-propyl silane (GPS-) modified sili ca column in combination with a Tricine buffer, a single protein band was identified as the inhibitor on IEF-PAGE gels. The inhibitor was id entified as a protein that has a mel. wt of approximately 17 and a pI of 5.1.