Extracellular ribonuclease from Rhizopus stolonifer: characteristics of an atypical--guanylic acid preferential--enzyme from ribonuclease T2 family.
An extracellular ribonuclease from Rhizopus stolonifer (designated as RNase Rs) was purified to homogeneity by chromatography on DEAE-cellulose followed by CM-cellulose. The Mr of the purified enzyme determined by gel filtration and SDS-PAGE is 25,000 and 28,200, respectively. RNase Rs is a glycoprotein and contains 10.5% neutral sugar. It is an acidic protein with a pI of 5.0 and has a blocked N-terminus. The optimum pH and temperature are 5.5 and 45 degrees C, respectively. RNase Rs shows high stability between pH 6.0-10.0. Divalent cations like Zn2+, Hg2+ and Cu2+ inhibit the enzyme activity whereas, mononucleotides does not have any significant effect. The enzyme cleaves RNA to 3'-mononucleotides via 2',3'-cyclic nucleotides, with preferential liberation of 2',3'-cyclic GMP, suggesting that RNase Rs is a guanylic acid preferential cyclizing RNase. Moreover, cyclic nucleotides generated are highly resistant to further hydrolysis.
Chacko
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R
Division of Biochemical Sciences, National Chemical Laboratory, Pune, India.
Shankar
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V
D002413:Cations, Divalent / Q000494:pharmacology; D004722:Endoribonucleases / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004795:Enzyme Stability; D006150:Guanine Nucleotides; D006863:Hydrogen-Ion Concentration; D008970:Molecular Weight; D012233:Rhizopus / Q000201:enzymology*; D013379:Substrate Specificity; D013696:Temperature
D002413:Cations, Divalent; D004791:Enzyme Inhibitors; D006150:Guanine Nucleotides; D004722:Endoribonucleases; C022543:ribonuclease T(2)