ATP‐GTP‐BINDING PROTEINS AND ENDOGENOUS ADP‐RIBOSYL TRANSFERASE IN Lemna paucicostata 441

— A crude extract containing membrane components of Lemna paucicostata was treated with 1% Lubrol PX and fractionated by gel nitration. Binding activities to non‐hydrolyzable analogues of ATP, [ 35 S]ATPγS (adenosine 5′[;γ‐thio]triphosphate) and that of GTP, [ 35 S]GTPγS (guanosine 5′[γ‐thiojtriphosphate) were detected in some fractions, and these activities were prevented in the presence of 0.1 mM ATP or GTP. ATP and GTP were 2 to 3 orders of magnitude more effective than CTP or UTP in preventing this binding activity. These fractions showed ATPase and GTPase activities with 1 nM [γ‐ 32 P]ATP or [γ– 32 P]GTP substrate. Analyses by sodium dodecyl sulfate polyacrylamide gel electrophoresis of these fractions after binding with [ 35 S]ATPγS or [ 35 S]GTP‐γ S revealed that these fractions contained [ 35 S]ATPγS and [ 35 S]GTPγS binding proteins with molecular weights of 53 000 and 60 000, respectively. Both of these proteins were [ 32 P]ADP‐ribosylated by endogenous ADP‐ribosyl transferase. Three proteins with molecular weights of 11 000, 12 000 and 13 000 which could bind [ 35 S]ATP7S or [‐ 35 S]GTP‐γ S were ADP‐ribosylated by endogenous ADP‐ribosyl transferase. Pertussis toxin stimulated ADP‐ribosylation of these proteins. Four proteins with molecular weight of 37 000, 50 000, 80 000 and 115 000 with P S S]ATP7S and [ ,3 S]GTP7S binding activities were also detected. The signal transduction of light to underlying clock mechanism in Lemna may be controlled by ATP‐GTP‐binding proteins and by the ADP‐ribosylation of these proteins.