4.6.1.18 an [RNA] containing cytidine + H2O = an [RNA]-3'-cytidine-3'-phosphate + a 5'-hydroxy-ribonucleotide-3'-[RNA] (1) overall reaction - 4.6.1.18 an [RNA] containing cytidine + H2O = an [RNA]-3'-cytidine-3'-phosphate + a 5'-hydroxy-ribonucleotide-3'-[RNA] enzymatic reaction mechanism, analysis of different versions, e.g. mechanism of Mathias and Rabin for catalysis of the hydrolysis of cytidine 2',3'-cyclic phosphate by RNase A, overview. Model of the RNase A-substrate complex, subsites of RNase A. Bn, Rn, and Rho_n are nucleobase-, ribose-, and phosphate-binding subsites, respectively 717258 4.6.1.18 an [RNA] containing cytidine + H2O = an [RNA]-3'-cytidine-3'-phosphate + a 5'-hydroxy-ribonucleotide-3'-[RNA] Gly38 and Glu111 are crucial for the catalytic activity 654423 4.6.1.18 an [RNA] containing cytidine + H2O = an [RNA]-3'-cytidine-3'-phosphate + a 5'-hydroxy-ribonucleotide-3'-[RNA] His119 and His12 play an important structural role in active site of RNase A 666170 4.6.1.18 an [RNA] containing cytidine + H2O = an [RNA]-3'-cytidine-3'-phosphate + a 5'-hydroxy-ribonucleotide-3'-[RNA] His12, His119 and Lys41 comprise the catalytic site, and several other amino acid residues serve as substrate binding subsites. The mutagenic replacement of Phe120 causes a positional change in His119 and that is a major cause in decreasing the activity of the enzyme. Phe120 is important in fixing the proper spatial position of His119 near the C-terminal region for efficient activity. Phe120 interacts not directly with His119, but with the hydrophobic core 657293 4.6.1.18 an [RNA] containing cytidine + H2O = an [RNA]-3'-cytidine-3'-phosphate + a 5'-hydroxy-ribonucleotide-3'-[RNA] protein of 128 amino acid residues, catalyses the cleavage of RNA specifically on the 3'-side of pyrimidine bases. The catalytic triad comprises His12, Lys41 and His119. The amino acid sequence of the enzyme is longer than that of its bovine counterpart, with four extra amino acid residues at the C-terminal region 656482 4.6.1.18 an [RNA] containing cytidine + H2O = an [RNA]-3'-cytidine-3'-phosphate + a 5'-hydroxy-ribonucleotide-3'-[RNA] protein with 124 amino acid residues and four intra-molecular disulfide bonds. In the presence of oxidized and reduced dithiothreitol at pH 8.0 and 25ºC, the enzyme folds through pathways involving a rapid pre-equilibrium resulting in an ensemble of three-disulfide intermediate species. Protein disulfide isomerase catalyzes the conversion of the intermediates to the native enzyme, by acting as both a chaperone and an oxidase on the on-pathway intermediate 655556 4.6.1.18 an [RNA] containing cytidine + H2O = an [RNA]-3'-cytidine-3'-phosphate + a 5'-hydroxy-ribonucleotide-3'-[RNA] pyrimidine-specific endoribonuclease which cleaves 3',5'-phosphodiester bonds of single strand RNA via transphosphorylation and subsequent hydrolysis reactions 656315 4.6.1.18 an [RNA] containing cytidine + H2O = an [RNA]-3'-cytidine-3'-phosphate + a 5'-hydroxy-ribonucleotide-3'-[RNA] RNase A catalyzes a well-characterized acid-base mechanism involving two histidines (His12 and His119) and a transition state stabilizing positive charge (Lys41). The transphosphorylation of a single-stranded RNA molecule by the enzyme yields a 2',3'-cyclic phosphomonoester intermediate, which can be expelled from the active site or hydrolyzed in a microscopic reverse reaction involving the same two histidines 729713 4.6.1.18 an [RNA] containing cytidine + H2O = an [RNA]-3'-cytidine-3'-phosphate + a 5'-hydroxy-ribonucleotide-3'-[RNA] sequential binding of the monomeric substrate in a concentration-dependent manner makes up the active site of the enzyme 656631 4.6.1.18 an [RNA] containing cytidine + H2O = an [RNA]-3'-cytidine-3'-phosphate + a 5'-hydroxy-ribonucleotide-3'-[RNA] specifically located basic residues, together with the lack of a negative charge and/or the presence of a glycine at position 38, may contribute to make the enzymatic degradation of the polyanionic double-helical substrate more efficient 654672 4.6.1.18 an [RNA] containing cytidine + H2O = an [RNA]-3'-cytidine-3'-phosphate + a 5'-hydroxy-ribonucleotide-3'-[RNA] the catalytic site of the enzyme is mainly composed of His12, His119, Gln11, Lys41 and Asp121. The conformation of Lys41 and Gln11 are pH dependent and their occurrence is correlated to the release of a sulfate ion from the active site at neutral pH. The sulfate anion is progressively released with pH and water molecules occupy the active site at pH 7.1. The enzyme adopts different conformational states in different pH conditions. In the protonated state, Lys41 points towards the active site both in the presence and in the absence of sulfate and acts as a general base during catalysis 654126 4.6.1.18 an [RNA] containing cytidine + H2O = an [RNA]-3'-cytidine-3'-phosphate + a 5'-hydroxy-ribonucleotide-3'-[RNA] the enzyme is composed of 124 amino acid residues. The amino acid residues involved in catalysis are His12, His119 and Lys41. The enzyme has six substrate binding subsites. One of them, B1, binds only to pyrimidine nucleotides and prefers to bind cytidine rather than uridine. Thr45 of the B1 subsite contributes to the enzyme substrate specificity and plays an important role in catalysis. Phe120 in the B1 subsite enhances substrate binding with the aid of its pi electron and hydrophobicity. Asn71 in the B2 subsite is responsible for productive interactions leading to efficient activity, and Glu111 in the same subsite contributes to substrate binding only in the binding of guanosine. Lys7, Arg10 and Gln11 in the P2 subsite also play an important role in catalysis. Some amino acid residues are located in the vicinity of the catalytic residues and contribute to the catalytic reaction by interacting with catalytic residues. Lys7, Arg10 and Lys66 maintain the optimum pKa of His12 and His119. Asp121 positions the proper tautomer of His119. Phe120 is responsible for the strict positioning of His119, and contributes to conformational stability. Tyr97 is involved in maintaining the correct position of Lys41. Cys65-Cys72 are located close to the catalytic and substrate binding residues and contribute to the proper spatial alignment of these residues 656308 4.6.1.18 an [RNA] containing cytidine + H2O = an [RNA]-3'-cytidine-3'-phosphate + a 5'-hydroxy-ribonucleotide-3'-[RNA] two isoforms of dimeric enzyme, D-I and D-II 655538 4.6.1.18 an [RNA] containing cytidine = an [RNA]-3'-cytidine-2',3'-cyclophosphate + a 5'-hydroxy-ribonucleotide-3'-[RNA] (1a) - 4.6.1.18 an [RNA] containing uridine + H2O = an [RNA]-3'-uridine-3'-phosphate + a 5'-hydroxy-ribonucleotide-3'-[RNA] (2) - 4.6.1.18 an [RNA] containing uridine = an [RNA]-3'-uridine-2',3'-cyclophosphate + a 5'-hydroxy-ribonucleotide-3'-[RNA] (2a) - 4.6.1.18 an [RNA]-3'-cytidine-2',3'-cyclophosphate + H2O = an [RNA]-3'-cytidine-3'-phosphate (1b) - 4.6.1.18 an [RNA]-3'-uridine-2',3'-cyclophosphate + H2O = an [RNA]-3'-uridine-3'-phosphate (2b) -