G-protein from Medicago sativa: functional association to photoreceptors.
G-protein subunits were characterized from Medicago sativa (alfalfa) seedlings. Crude membranes and GTP-Sepharose-purified fractions were electrophoresed on SDS/polyacrylamide gels and analysed by Western blotting with 9193 (anti-alpha common) and AS/7 (anti-alpha t, anti-alpha i1 and anti-alpha i2) polyclonal antibodies. These procedures led to the identification of a specific polypeptide band of about 43 kDa. Another polypeptide reacting with the SW/1 (anti-beta) antibody, of about 37 kDa, was also detected. The 43 kDa polypeptide bound specifically [alpha-32P]GTP by a photoaffinity reaction and was ADP-ribosylated by activated cholera toxin, but not by pertussis toxin. Irradiation of etiolated Medicago sativa protoplast preparations at 660 nm for 1 min produced a maximal increase in the guanosine 5'-[gamma-thio]triphosphate (GTP[35S])-binding rate. After this period of irradiation, the binding rate tended to decrease. The effect of a red-light (660 nm) pulse on the binding rate was reversed when it was immediately followed by a period of far-red (> 730 nm) illumination. These results may suggest that activation of GTP[S]-binding rate was a consequence of conversion of phytochrome Pr into the Ptr form.
Muschietti
J P
JP
Instituto de Investigaciones en Ingeniería Genética y Biología Molecular, Facultad de Ciencias Exactas y Naturales, Buenos Aires, Argentina.
Martinetto
H E
HE
Coso
O A
OA
Farber
M D
MD
Torres
H N
HN
Flawia
M M
MM
D000246:Adenosine Diphosphate Ribose / Q000378:metabolism; D000595:Amino Acid Sequence; D015153:Blotting, Western; D002462:Cell Membrane / Q000737:chemistry; D002772:Cholera Toxin / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; D019204:GTP-Binding Proteins / Q000032:analysis* / Q000378:metabolism; D006160:Guanosine Triphosphate / Q000378:metabolism; D008027:Light; D000455:Medicago sativa / Q000737:chemistry* / Q000378:metabolism; D008969:Molecular Sequence Data; D010786:Photoreceptor Cells / Q000378:metabolism*; D013462:Sulfur Radioisotopes
D013462:Sulfur Radioisotopes; D000246:Adenosine Diphosphate Ribose; D006160:Guanosine Triphosphate; D002772:Cholera Toxin; D019204:GTP-Binding Proteins