NTP-binding proteins were detected in the plasma membrane purified from elongating third internodes of etiolated pea (
Pisum sativum Alaska) seedlings. After [α-
32P] ATP and [α-
32P] GTP bound to proteins in the plasma membrane, the reaction mixtureas were UV crosslinked, then analyzed by SDS-polyacrylamide gel electrophoresis (PAGE). Pretreatment of the membrane fraction by a Ras-specific antibody efficiently blocked the binding of [α-
32P] ATP and [α-
32P] GTP. Several proteins in the plasma membrane were [
32P] ADP-ribosylated by endogenous ADP-ribosyl transferase, and by cholera and pertussis toxins. The [
32P] ADP-ribosylation of these proteins by endogenous ADP-ribosyl transferase was partly reduced by pretreating the plasma membrane with a Ras-specific antibody. Most of the [α-
32P]ATP binding to several NTP-binding proteins was inhibited efficiently by 10
-3 M ATP. The binding of [α-
32P] GTP was inhibited more efficiently, however, by 10
-3 M ATP or UTP than by 10
-3 M GTP or CTP. Red light irradiation of the third internodes stimulated the binding of [α-
32P] ATP and [α-
32P] GTP to 16, 21, 32, 34, 37, 71 and 92 kDa proteins, as analyzed by UV-induced crosslinking followed by SDS-PAGE, and the results were supported by using Triton X-100-PAGE without UV-induced crosslinking. Among these, the amount of a 37 kDa protein exhibiting cross-reactivity with α subunit of transducin-sepcific antibody, was rapidly reduced in the plasma membrane after red light irradiation of the third internodes. A 30 kDa protein showing cross reactivity with β, γ subunit-specific antibody, however, stayed relatively unchanged.
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