No abstract

A complete analysis of the 220 MHz proton magnetic resonance spectrum of aqueous uridine is reported. From the data a model for the molecular conformation is presented and compared with that of p-pseudouridine. It is concluded that in both compounds the ribose rings are in rapid equilibrium between classical puckered structures. The temperature-independence of the ribose proton coupling constants and chemical shifts suggests that all the conformers involved in this equilibrium have very similar energies. Both compounds exhibit a preference for the gauche-gauche rotamer about the exocyclic 4' -5' bond; this conclusion is shown to be independent of the parameters in the Karplus equation or the energy minima chosen for the rotamers. The anti conformation of the uracil base is shown to exist in both compounds. It is proposed that the special structural significance of p-pseudouridine in transfer RNA must be due to the potential hydrogen bond that may be formed by the nitrogen atom at position one in uracil.

Four glycopeptides have been purified by Dowex and Bio-Gel P2 chromatography from Pronase digests of hen ovalbumin. The high-resolution proton magnetic resonance spectra of these glycopeptides and various products of their enzymatic digestion have been obtained at 360 MHz. By use of information derived from the spectra of a number of model compounds, an unambiguous assignment of all C1-H and Man C2-H resonances in the spectra can be made. On this basis structures are proposed for the four glycopeptides which are identical with those structures previously deduced from destructive chemical methods.

High field magnetic resonance spectroscopy has been utilized to deduce the primary structure of the glycopeptides from a human myeloma gamma 1-immunoglobulin G (Tem). The major structures found belong to the biantennary complex class of glycopeptides, with a minor (5%) fraction belonging to the bisected biantennary complex class. In the biantennary class, three structures were present with different residues at the termini of the alpha Man(1-6) and alpha Man(1-3) arms: (i) with beta Gal(1-4) and alpha NeuNAc(2-6), respectively (33%); (ii) with beta Gal(1-4) and beta Gal(1-4), respectively (45%); and (iii) beta Gal(1-4) and beta GlcNAc(1-2), respectively (17%). In the bisected biantennary class only the latter termini were found for the two arms. These results suggest that the galactosyl transferase in these cells has a preference for the beta GlcNAc(1-2) of the alpha Man(1-6) arm and that the sialyltransferase has a preference for the beta Gal(1-4) of the alpha Man(1-3) arm.

A computer analysis of the entire 100-MHz nmr spectrum of the modified nucleoside /3-pseudouridine, ß-, in aqueous solution is reported. The analysis was confirmed by spin-tickling and spin-decoupling experiments. The results are used to determine a model for the conformation of the nucleoside. An equilibrium between various puckered ring conformations is proposed. The populations of the various rotamers about the Cv-Cs-bond are evaluated; a preference for the gauche-gauche rotamer is indicated. Comparison with the available data for uridine indicates that the two compounds have almost identical ribose conformations, and that the uracil moiety in (47) R.