Giulio L. Cantoni

Studies on soluble ribonucleic acid of rabbit liver III. Preparation and properties of rabbit-liver soluble RNA

Abstract Soluble RNA has been prepared in relatively large amounts from rabbit liver by a procedure involving extraction of the “pH-5 enzymes” with hot NaCl. The product is highly homogeneous with respect to molecular size and heterogeneous with respect to biological activity inasmuch as it can act as acceptor for at least 15 different activated amino acids. The nucleotide composition of rabbit-liver soluble RNA has been determined quantitatively by column chromatography, under conditions which permit the separation of 5 minor components: (i) 5-hydroxymethylcytidine ribotide; (ii) 6-methylaminopurine ribotide; (iii) 2-dimethylamino-6-hydroxypurine ribotide; (iv) 1-methylguanine ribotide; and (v) 5-ribosyluracil ribotide; in addition to the 4 major ones: cytidylic acid; adenylic acid; guanylic acid; and uridylic acid. The minor components represent approx. 10% of the total nucleotides. Soluble RNA is markedly resistant to enzymic degradation by a variety of RNA-ases. The significance of these findings is discussed.

Studies on soluble ribonucleic acid of rabbit liver IV. Physical properties and structure

Abstract An investigation of the physical properties of rabbit-liver soluble RNA in 0.2M NaCl, revealed that the s 20,w 0 and the M are 4.2 and 23 300, respectively; the specific absorbancy and molar absorbancy per phosphate are 23.0 ml/mg/cm, and 7.7 ml/μmole/cm, respectively; the average nucleotide weight is 345 g/mole of nucleotide (i.e., 9.0 % phosphorous), yielding a chain length of 68 nucleotides per chain; and the apparent specific volume and intrinsic viscosity (after correction for shear dependence) are 0.47 ml/g and 0.15 dl/g, respectively. Ultracentrifugal analysis revealed that the preparation, consisting of a mixture of 15 amino acid-acceptor species, possesses about 12% sedimentation heterogeneity at low concentration, which increases due to aggregation as the concentration is raised. At low salt concentrations, s responds to a primary charge effect, but it is independent of salt concentration at the level used in this investigation. The absorbancy of the solutions, on the other hand, is relatively unaffected by ionic strength. These data were examined in terms of the existing theories of molecular configuration in solution. It was concluded that soluble RNA has a highly asymmetric, relatively rigid secondary structure, which is more like that of DNA than of high-molecular-weight RNA.

The synthesis of methionine by enzymic transmethylation: VII. Existence of two separate homocysteine methylpherases on mammalian liver

Abstract In addition to the enzyme thetin-homocysteine methylpherase, rat and horse livers contain a second enzyme capable of catalyzing the methylation of homocysteine to form methionine. This enzyme differs from thetin-homocysteine methylpherase (a) in its substrate specificity which is much more favorable to the naturally occurring methyl donor betaine; (b) in its behavior towards calcium phosphate and alumina gels, and Sephadex G-75; (c) in its intracellular distribution; and (d) in its concentration in neonatal and regenerating rat liver. The physiological significance of the two homocysteine methylpherases is discussed.