Bimodal action of alkaline earth cations on Dictyostelium discoideum ribonuclease P activity.
The ribonucleoprotein ribonuclease P (RNase P) cleaves all tRNA precursors endonucleolitically to produce the mature 5'-end. Dictyostelium discoideum RNase P displays an absolute requirement for Mg2+. Only the alkaline earth cations Ca2+, Sr2+, and Ba2+, under appropriate conditions can substitute to some extent for Mg2+. The transition metals Mn2+, Co2+, Ni2+, and Cd2+ are efficient inhibitors of the enzyme activity. Ca2+, Sr2+ and Ba2+, in the presence of Mg2+, exhibit a bimodal action at the kinetic phase of the reaction. Kinetic analysis of the activation phase revealed that Ca2+, Sr2+, or Ba2+ attached on a specific site of RNase P act as nonessential-noncompetitive activators. Further additions of Ca2+, Sr2+, or Ba2+ cause noncompetitive inhibition on the RNase P reaction, indicating that RNase P possesses a second binding site responsible for the inhibitory effect of Ca2+, Sr2+, and Ba2+. Both activator and inhibitory sites can be occupied by Ca2+, Sr2+, or Ba2+ at the same time.
Tekos
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Department of Biochemistry, School of Medicine, University of Patras, Greece.
Stathopoulos
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C
Drainas
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D
D000818:Animals; D001464:Barium / Q000494:pharmacology; D002104:Cadmium / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology; D002413:Cations, Divalent; D003035:Cobalt / Q000494:pharmacology; D004023:Dictyostelium / Q000201:enzymology*; D004722:Endoribonucleases / Q000737:chemistry / Q000378:metabolism*; D004789:Enzyme Activation / Q000187:drug effects; D006868:Hydrolysis / Q000187:drug effects; D008274:Magnesium / Q000494:pharmacology; D008345:Manganese / Q000494:pharmacology; D008673:Metals, Alkaline Earth / Q000494:pharmacology*; D009532:Nickel / Q000494:pharmacology; D016337:RNA, Catalytic / Q000737:chemistry / Q000378:metabolism*; D043262:Ribonuclease P; D013324:Strontium / Q000494:pharmacology
D002413:Cations, Divalent; D008673:Metals, Alkaline Earth; D016337:RNA, Catalytic; D002104:Cadmium; D001464:Barium; D003035:Cobalt; D008345:Manganese; D009532:Nickel; D004722:Endoribonucleases; D043262:Ribonuclease P; D008274:Magnesium; D002118:Calcium; D013324:Strontium