The relation of polyphenoloxidase in leaf extracts to the instability of cucumber mosaic and other plant viruses

RESP-492

Copper-dependent and iron-dependent inactivations of cucumber mosaic virus by polyphenols

RESP-492

PVX-Q: an Infective Product of Potato Virus X and a Leaf o-Quinone

When potato virus X (PVX) is exposed to enzymically oxidizing chlorogenic acid, and re-isolated, some of its properties are changed. Its u.v. spectrum is modified and centrifuged pellets are coloured: its u.v. fluorescence is diminished, a longer-wave fluorescence is introduced: it produces less colour with 2,4,6-trinitrobenzene sulphonic acid, and moves faster during electrophoresis. There is, however, little or no loss of infectivity in the course of the reaction. The results suggest that PVX combines with chlorogenoquinone to produce a modified but infective virus (PVX-Q) and it is thought that this reaction may occur naturally

Chemical Modification of the Lysine-Amino Groups of Potato Virus X

Potato virus X reacted with reagents commonly used for protein amino groups, and some of its properties were changed. 2,4,6-trinitrobenzenesulphonic acid, pyridoxal-5-phosphate and methyl picolinimidate altered its absorption spectrum; the last two altered its fluorescence spectrum, and the first two altered its electrophoretic mobility. These reagents did not necessarily inactivate the virus; preparations judged to contain two modified amino groups per protein subunit retained 50 to 100% of their initial infectivity. This supports the previous conclusion that PVX-Q, an infective product of PVX and an oxidized leaf phenol, contains modified lysine ε-amino groups

Polyphosphates excreted by wax-moth larvae (Galleria mellonella L. and Achroia grisella Fabr.)

RESP-386

The Purification and Properties of One of the ‘b’ Proteins from Virus-Infected Tobacco Plants

The b1 protein, produced in leaves of Nicotiana tabacum cv. Xanthi-nc following infection with tobacco mosaic virus, has been purified to homogeneity by a procedure which involves gel chromatography and absorption on to DEAE-cellulose. One gel chromatography step was sufficient when the procedure was applied to leaf extracts made in an acid buffer, whereas two were necessary with extracts made at pH 8. The final product migrates as a single protein band on electrophoresis in both acrylamide and SDS-acrylamide gels. Its mol. wt. is estimated to be 15000 by electrophoresis and 14200 by ultracentrifugation. Amino acid analysis suggests that it contains about 136 residues of which 39 are potentially acidic, 13 basic and 16 aromatic. The absorbance coefficient A 1% 280 nm is estimated to be 18.9. No evidence was found for the presence of a nucleotide component

Cross-linking of the Subunits of Potato Virus X with Di-imidates

The protein subunits of the XN strain of potato virus X (PVX) were cross-linked by di-imidates to produce a series of polymers in the proportion expected from the random cross-linking of subunits in an extensive heterologous array. Polymerization of the subunits of chemically modified forms of the virus, as well as of other strains, suggests that the cross-links are heterogeneous, and may, but need not, involve the two amino groups that have been previously characterized as either reacting with chlorogenoquinone or being sensitive to trypsin

An Infective Pyridoxyl-derivative of Potato Virus X: PVX-PLP

he reduced initial product (PVX-PLP) of the reaction of pyridoxyl 5′-phosphate (PLP) and particles of potato virus X (PVX) contains about 1 (0.6 to 1.2) molecules of PLP per protein subunit and is infective. Hydrolysates of the protein contain N-ε-pyridoxyl-lysine. PVX-PLP reacts with chlorogenoquinone to 1/4 of the extent of PVX; similarly, PVX which has reacted with chlorogenoquinone (PVX-Q1) binds only 1/3 to 1/5 as much PLP as does PVX. PVX-PLP contains two types of fluorescent subunit which can be separated by electrophoresis in SDS-acrylamide gels: one of these is fluorescent and is not degraded by brief exposure to trypsin, whereas the other is degraded to a smaller form which is also fluorescent. Tryptic digests of the protein from PVX-PLP contain at least two fluorescent peptides. It is argued that PLP reacts with two lysine ε-amino groups of PVX, one of which also reacts with chlorogenoquinone, and the other of which is recognized by trypsin. Protein isolated from PVX reacts with up to 6 molecules of PLP. The conformation of the subunits in the intact virus apparently makes many ε-amino groups inaccessible to PLP