Improved perfusion quantification in FAIR imaging by offset correction.

Perfusion quantification using pulsed arterial spin labeling has been shown to be sensitive to the RF pulse slice profiles. Therefore, in Flow-sensitive Alternating-Inversion Recovery (FAIR) imaging the slice selective (ss) inversion slab is usually three to four times thicker than the imaging slice. However, this reduces perfusion sensitivity due to the increased transit delay of the incoming blood with unperturbed spins. In the present article, the dependence of the magnetization on the RF pulse slice profiles is inspected both theoretically and experimentally. A perfusion quantification model is presented that allows the use of thinner ss inversion slabs by taking into account the offset of RF slice profiles between ss and nonselective inversion slabs. This model was tested in both phantom and human studies. Magn Reson Med 46:193-197, 2001.

Effects of oral D-tagatose, a stereoisomer of D-fructose, on liver metabolism in man as examined by 31P-magnetic resonance spectroscopy.

D-tagatose, which is a stereoisomer of D-fructose, is phosphorylated to D-tagatose-1-phosphate by fructokinase in the liver. Because of a slow degradation rate of D-tagatose-1-phosphate, this substance may accumulate, and ingested D-tagatose may therefore cause a longer lasting reduction in inorganic phosphate (Pi) and adenosine triphosphate (ATP) levels in the liver compared with D-fructose. Similar to what is seen in patients with hereditary fructose intolerance, this may increase purine nucleotide degradation and thereby increase uric acid production. The effect of 30 g D-tagatose or D-fructose administered orally on ketohexose-1-phosphates, ATP, and Pi levels in the liver was studied by 31P-magnetic resonance spectroscopy (PMRS) in 5 young male volunteers. Blood and urine were collected to detect a possible increased uric acid production. A peak at 5.2 ppm assigned as D-tagatose-1-phosphate equivalent to about 1 mmol/L was found in the spectrum within 30 minutes after D-tagatose was administered in all subjects. Concomitantly, ATP was reduced by about 12% (P < .05). Both effects had vanished after 150 minutes. Serum uric acid concentration was increased by 17% 50 minutes after D-tagatose (P < .05) and did not reach baseline level when the experiment was terminated 230 minutes after the load. Although renal fractional extraction of uric acid decreased by approximately 12%, this could not explain the acute hyperuricemic effect of D-tagatose. No changes in 31PMRS spectra or serum uric acid concentration were found after D-fructose. These results suggest that a moderate intake of D-tagatose may affect liver metabolism by phosphate trapping despite the fact that the sugar may only be incompletely absorbed in the gut.

Solution structure of reduced plastocyanin from the blue-green alga Anabaena variabilis.

The three-dimensional solution structure of plastocyanin from Anabaena variabilis (A.v.PCu) has been determined by nuclear magnetic resonance spectroscopy. Sixty structures were calculated by distance geometry from 1141 distance restraints and 46 dihedral angle restraints. The distance geometry structures were optimized by simulated annealing and restrained energy minimization. The average rms deviation from the mean structure for the 20 structures with the lowest total energy is 1.25 A for the backbone atoms and 1.75 A for all heavy atoms. Overall, the global tertiary fold of A.v.PCu resembles those of other plastocyanins which have been structurally characterized by X-ray diffraction and NMR methods. This holds even though A.v.PCu is longer than any other known plastocyanins, contains far less invariant amino acid residues, and has an overall charge that differs considerably from those of other plastocyanins (+1 vs -9 +/- 1 at pH > or = 7). The most striking feature of the A.v. PCu structure is the absence of the beta-turn, formed at the remote site by residues (58)-(61) in most higher plant plastocyanins. The displacement caused by the absence of this turn is compensated for by an extension of the small helix [from Ala53(51) to Ser60(58) in A.v.PCu] found in other plastocyanins. Moreover, the extra residues of A.v.PCu from Pro77 to Asp79 form an appended loop. These two features allow A.v.PCu to retain almost the same global fold as observed in other plastocyanins. From a comparison with the structures of other plastocyanins it is concluded that the lack of negatively charged residues at the remote site, rather than the specific structure of A.v.PCu, is the main reason for the failure of the remote site of this plastocyanin to function as a significant electron transfer site.

Linear prediction enhancement of 2D heteronuclear correlated spectra of proteins.

Linear prediction has been used to extrapolate the t1 domain of natural abundance 1H-13C correlated two-dimensional (2D) FIDs of insulin. The FIDs were obtained by two different heteronuclear correlation experiments, one that utilizes heteronuclear multiple-quantum coherence during t1, and one that utilizes 13C single-quantum coherence. It is shown that the enhancement of the resolution and sensitivity in the F1 dimension of the Fourier transform spectrum that results from the linear prediction extrapolation allows the t1 domain to be confined to a relatively short time period where the signal intensity is at maximum. In particular, it is found that the enhancement thus obtained is sufficiently good to allow an observation of the difference between the F1 line widths in the single-quantum and double-quantum coherence spectra.