Purification and characterization of a probable light receptor with kinase activity from beet root plasma membranes.
A 120-kDa glycoprotein was found in beet root (Beta vulgaris L.) plasma membranes. This protein could be phosphorylated in a Ca2+-independent manner. Its carbohydrate moiety was composed of both O-linked galactose-beta(1-3)-N-acetylgalactosamine disaccharides (which bind peanut agglutinin) and N-linked concanavalin A (ConA)-binding oligosaccharides. The phosphorylation of this protein was rapid, half-saturated with 6 microM ATP and higher at alkaline pH values. This protein was phosphorylated more efficiently with Mn-ATP as substrate than with Mg-ATP. This phosphorylation increased when plasma membranes were illuminated with low-fluence blue light, a fact suggesting that the 120-kDa glycoprotein could be similar to phototropin: a blue-light photoreceptor involved in phototropism. This protein was purified using a ConA-Sepharose column. The phosphorylation of the purified protein could be observed, but it was much lower than that of the 120-kDa protein in plasma membranes. In addition, it was not enhanced by light. Some possible explanations for this photosensitivity loss are discussed.
Raya
J C
JC
Departamento de Biotecnología y Bioquímica, Centro de Investigación y de Estudios Avanzados del IPN, Irapuato Gto, México.
González de la Vara
L E
LE
D000255:Adenosine Triphosphate / Q000494:pharmacology; D027461:Beta vulgaris / Q000378:metabolism* / Q000528:radiation effects; D002118:Calcium / Q000494:pharmacology; D050260:Carbohydrate Metabolism; D002462:Cell Membrane / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D008027:Light; D008562:Membrane Glycoproteins / Q000302:isolation & purification* / Q000378:metabolism / Q000528:radiation effects; D010766:Phosphorylation / Q000187:drug effects / Q000528:radiation effects; D010770:Phosphotransferases / Q000302:isolation & purification* / Q000378:metabolism / Q000528:radiation effects; D018517:Plant Roots / Q000378:metabolism* / Q000528:radiation effects
D008562:Membrane Glycoproteins; D000255:Adenosine Triphosphate; D010770:Phosphotransferases; D002118:Calcium