TOMATO POLYGALACTURONASE EXTRACTABILITY

The extractability of polygalacturonase (PG) activity from alcohol-ins oluble solids (AIS) prepared from red-ripe tomato pericarp tissue was investigated using acetate (pH 4.5), citrate (pH 4.5) and MES (pH 6.0) buffers. The acetate buffer was also investigated with increasing con centrations of NaCl, CaCl2, MgCl2, ethylenediaminetetraacetic acid (ED TA) or eglycol-bis(beta-aminoethylether)-N,N'-tetraacetic acid (EGTA). Heat treatment of AIS to prepare control material suppressed PG extra ctability but not in situ PG activity, as evidenced by the release of significant quantities of soluble uronides into extraction media. With only a single extraction, acetate buffer containing > I M NaCl yielde d the greatest amount of PG activity (> 50% of maximum extractability) , with MES buffer being only marginally less efficient However, 3 succ essive extractions over a 2 h period yielded significantly greater amo unts of PG activity. The greatest yields of PG activity were obtained by successive extraction with parent MES and acetate buffers. There ap peared to be little benefit in adding NaCl or a chelating agent to the extraction medium. Use of these extractants is suggested to have led to losses of PG activity during dialysis, via coprecipitation of PG pr otein with otherwise soluble uronide material that was released in gre ater quantities when these extractants were used. Increasing CaCl2 and MgCl2 concentrations reduced the amount of extracted PG activity simi larly, to about 50% of maximum levels with successive extractions.