Ribonuclease inhibitor. Prepn from yeast ribonucleic acid: see refs under 2′-Cytidylic Acid. Prepn by pancreatic-ribonuclease-catalyzed ring opening of dicyclohexylguanidinium cytidine 2′,3′-cyclic phosphate: Lohrmann, Khorana, J. Am. Chem. Soc. 86, 4188 (1964). X-ray analysis studies of orthorhombic form: Alver, Furberg, Acta Chem. Scand. 13, 910 (1959); Sundaralingam, Jensen, J. Mol. Biol. 13, 914 (1965); of monoclinic form: Bugg, Marsh, ibid. 25, 67 (1967). Reviews: See Cytidine.