THE GROWTH-FACTOR FROM PLEROCERCOIDS OF SPIROMETRA MANSONOIDES IS BOTH A GROWTH-HORMONE AGONIST AND A CYSTEINE PROTEINASE

Plerocercoids of the tapeworm Spirometra mansonoides produce a substan ce that stimulates growth of experimental hosts. We report purificatio n of plerocercoid growth factor (PGF) to homogeneity by a process invo lving isolation and solubilization of plerocercoid membranes, isoelect ric point selection by chromatofocusing chromatography or preparative isoelectric focusing, and anion-exchange chromatography. A radiorecept or assay (RRA) for human growth hormone (hGH) was used to detect PGF a nd purity of the 27.5-kDa protein was judged by sodium dodecyl sulfate -polyacrylamide gel electrophoresis (SDS-PAGE). Proteolytic activity w as detected in the 27.5-kDa protein by gelatin substrate PAGE. Charact erization of PGF as a neutral cysteine proteinase was based on substra te and inhibitor specificities and dependence on pH and thiol-containi ng reagents. The association of hGH agonist and proteinase activities was shown by comparing RRA and hydrolytic activities in the presence a nd absence of the cysteine proteinase inhibitor E-64.