VIEW ARTICLE

The Effects of Enzymatic Digestion on the Molecular Weight and Antigenic Specificity of Potato Virus X Protein. J. F. Shepard, Department of Botany and Microbiology, Montana State University, Bozeman 59715; G. A. Secor, Department of Botany and Microbiology, Montana State University, Bozeman 59715. Phytopathology 62:1154-1160. Accepted for publication 15 April 1972. DOI: 10.1094/Phyto-62-1154.

Two forms of potato virus X (PVX) protein were exposed to proteolytic enzymes in tobacco leaf homogenates and to trypsin. Both enzyme preparations reduced the molecular weight of assembled PVX protein ca. 15%, but did not simultaneously influence the antigenic specificity of the assembled or subsequently dissociated subunits. Treatment of chemically degraded PVX protein (D-protein) with either enzyme preparation, however, resulted in a pronounced reduction in subunit molecular weight with polypeptides of less than 12,000 mol wt being produced. A concomitant, progressive change in antigenic specificity occurred when subunit molecular weight decreased from ca. 23,000 to less than 12,000 even though the latter peptides were still precipitated by D-protein antiserum. The effects of the proteolytic enzyme(s) in tobacco sap on D-protein and on assembled PVX protein could be inhibited through the addition of sodium diethyldithiocarbamate (DIECA) to the extraction medium. Trypsin inhibitors, in contrast, were not inhibitory. The influence of tobacco enzyme(s) on a third form of PVX protein; i.e., the soluble antigen associated with PVX infection (free-protein), was also investigated. Acrylamide gel electrophoresis suggested that even in the presence of DIECA, the majority of polypeptides in free-protein preparations were of a molecular weight less than 20,000, although some with molecular weights up to 29,000 were also detected when DIECA was used during their isolation.