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

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Abstract
The reduced initial product (PXV-PLP) of the reaction of pyridoxyl 5''-phosphate (PLP) and particles of potato virus X (PVX) contains about 1 (0.6-1.2) molecules of PLP/protein subunit and is infective. Hydrolysates of the protein contain N-.epsilon.-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 1/3-1/5 as much PLP as does PVX. PVX-PLP contains 2 types of fluorescent subunit which can be separated by electrophoresis in SDS[sodium dodecyl sulfate]-acrylamide gels: one of these is fluorescent and is not degraded by brief exposure to trypsin, but the other is degraded to a smaller form which is also fluorescent. Tryptic digests of the protein from PVX-PLP contain at least 2 fluorescent peptides. PLP reacts with 2 lysine .epsilon.-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 .epsilon.-amino groups inaccessible to PLP.