Two-dimensional nuclear magnetic resonance spectroscopy

Great spectral simplification can be obtained by spreading the conventional one-dimensional nuclear magnetic resonance (NMR) spectrum in two independent frequency dimensions. This so-called two-dimensional NMR spectroscopy removes spectral overlap, facilitates spectral assignment, and provides a wealth of additional information. For example, conformational information related to interproton distances is available from resonance intensities in certain types of two-dimensional experiments. Another method generates 1H NMR spectra of a preselected fragment of the molecule, suppressing resonances from other regions and greatly simplifying spectral appearance. Two-dimensional NMR spectroscopy can also be applied to the study of 13C and 15N, not only providing valuable connectivity information but also improving sensitivity of 13C and 15N detection by up to two orders of magnitude.

Physico-chemical and microbiological comparison of nystatin, amphotericin A and amphotericin B, and structure of amphotericin A

Two polyene antibiotics, nystatin and amphotericin A, were compared by physico-chemical and microbiological methods. The two antibiotics were found to have the same molecular weight, 926, by plasma desorption and electron-impact MS. However, 13C NMR spectrometry and HPLC studies indicated that the two molecules are different. The 200 MHz NMR studies indicated a chemical environment of 24 carbons of amphotericin A identical with that of the carbons of amphotericin B and nystatin. The structure of amphotericin A is identical with that of amphotericin B, except that there is a single bond between carbons 28 and 29 instead of a double bond, as shown by two-dimensional NMR studies.

Escherichia coli K51 and K93 capsular polysaccharides are crossreactive with the group A capsular polysaccharide of Neisseria meningitidis. Immunochemical, biological, and epidemiological studies

Eleven Escherichia coli strains, crossreactive with the capsular polysaccharide (CPS) of Neisseria meningitidis group A (GrA), were detected among 645 stool isolates from healthy families in Cairo, Egypt. 10 of these strains were of the O107:K93:H27 or O107:K93:SP serotypes and may be considered descendents of a single bacterium or as a clone. The remaining crossreactive strain was of the O7:K51:H18 serotype. None of the 11 strains produced enterotoxins and none were enteroinvasive. The purified CPS of these E. coli strains, as well as a polysaccharide (PS) from B. pumilis, strain Sh17, precipitated with equine GrA (H49) antiserum. A partial identity between the E. coli K93, K51 and Sh17 PS on the one hand and the GrA CPS on the other was observed by double immunodiffusion when reacted against the H49 antiserum. Four K93 strains and one K51 strain were found among 320 E. coli strains from patients at the Clinical Center, National Institutes of Health, and three K93 strains were found in 105 stool samples from children in Copenhagen. The data from these three surveys suggest that these crossreactive E. coli are common organisms and could serve as a stimulus for "natural" GrA CPS antibodies. Quantitative precipitation analysis showed that K51, K93, and Sh17 PS precipitated 25, 46.8, and 50% of H49 antibodies, respectively. Absorption of H49 antiserum with the GrA CPS removed its precipitating activity with the E. coli K93, K51, and Sh17 PS. Absorption of H49 antiserum with either K51 CPS or Sh17 PS removed the homologous crossreactivity only, whereas K93 CPS absorbed both K93 and K51 reactivities. Antibodies, raised by intravenous injection of formalinized E. coli K93 or K51 cells into rabbits, precipitated with GrA CPS and were bactericidal against GrA meningococci. The crossreaction between the E. coli K93 and the GrA CPS was unexpected since these two CPS are compositionally so dissimilar.

15N-labeled Escherichia coli tRNAfMet, tRNAGlu, tRNATyr, and tRNAPhe. Double resonance and two-dimensional NMR of N1-labeled pseudouridine

The N1 imino units in Escherichia coli tRNAfMet, tRNAGlu, tRNAPhe, and tRNATyr were studied by 1H-15N NMR using three different techniques to suppress signals of protons not attached to 15N. Two of the procedures, Fourier internuclear difference spectroscopy and two-dimensional forbidden echo spectroscopy permitted 1H and 15N chemical shifts to be measured simultaneously at 1H sensitivity. The tRNAs were labeled by fermentation of the uracil auxotroph S phi 187 on a minimal medium containing [1-15N]uracil. 1H and 15N resonances were detected for all of the N1 psi imino units except psi 13 at the end of the dihydrouridine stem in tRNAGlu. Chemical shifts for imino units in the tRNAs were compared with "intrinsic" values in model systems. The comparisons show that the A X psi pairs at the base of the anticodon stem in E. coli tRNAPhe and tRNATyr have psi in an anti conformation. The N1 protons of psi in other locations, including psi 32 in the anticodon loop of tRNAPhe, form internal hydrogen bonds to bridging water molecules or 2'-hydroxyl groups in nearby ribose units. These interactions permit psi to stabilize the tertiary structure of a tRNA beyond what is provided by the U it replaces.

Multiple quantum two-dimensional 1H--15N nuclear magnetic resonance spectroscopy: chemical shift correlation maps for exchangeable imino protons of Escherichia coli tRNAMetf in water

A procedure based on multiple quantum two-dimensional nuclear magnetic resonance spectroscopy is described for generation of 1H--15N chemical shift correlation maps. The method is used to obtain 15N chemical shifts for the exchangeable imino protons in 1H--15N units of site-specifically labeled Escherichia coli tRNAMetf in water. The high sensitivity and excellent chemical shift dispersion of the multiple quantum two-dimensional technique make it ideally suited for studying protonated nitrogens by NMR.