Aim: Purification and characterization of an aminotransferase (AT) specific for the degradation of branched-chain amino acids from Lactobacillus paracasei subsp. paracasei CHCC 2115. Methods and Results:The purification protocol consisted of anion exchange chromatography, affinity chromatography and hydrophobic interaction chromatography. The enzyme was found to exist as a monomer with a molecular mass of 40-50 kDa. The AT converted isoleucine, leucine and valine at a similar rate with a-ketoglutarate as the amino group acceptor; minor activity was shown for methionine. The enzyme had pH and temperature optima of 7AE3 and 43°C, respectively, and activity was detected at the pH and salt conditions found in cheese (pH 5AE2, 4% NaCl). Hg 2+ completely inhibited the enzyme, and the inhibition pattern was similar to that for pyridoxal-5¢-phosphate-dependent enzymes, when studying the effect of other metal ions, thiol-and carbonylbinding agents. The N-terminal sequence of the enzyme was SVNIDWNNLGFDYMQLPYRYVAHXKDGVXD, and had at the amino acid level, 60 and 53% identity to a branched-chain amino acid AT of Lact. plantarum and Lactococcus lactis, respectively. Conclusions: The results suggest that Lact. paracasei subsp. paracasei CHCC 2115 may contribute to development of flavour in cheese. Significance and Impact of the Study: The findings of this work contribute to the knowledge of transamination performed by cheese-related bacteria, and in the understanding and control of amino acid catabolism and the production of aroma compounds.
To demonstrate a novel method for tracking of head movements during MRI using electroencephalography (EEG) hardware for recording signals induced by native imaging gradients. Theory and Methods: Gradient switching during simultaneous EEG-fMRI induces distortions in EEG signals, which depend on subject head position and orientation. When EEG electrodes are interconnected with high-impedance carbon wire loops, the induced voltages are linear combinations of the temporal gradient waveform derivatives. We introduce head tracking based on these signals (CapTrack) involving 3 steps: (1) phantom scanning is used to characterize the target sequence and a fast calibration sequence; (2) a linear relation between changes of induced signals and head pose is established using the calibration sequence; and (3) induced signals recorded during target sequence scanning are used for tracking and retrospective correction of head movement without prolonging the scan time of the target sequence. Performance of CapTrack is compared directly to interleaved navigators. Results: Head-pose tracking at 27.5 Hz during echo planar imaging (EPI) was demonstrated with close resemblance to rigid body alignment (mean absolute difference: [0.14 0.38 0.15]-mm translation, [0.30 0.27 0.22]-degree rotation).Retrospective correction of 3D gradient-echo imaging shows an increase of average edge strength of 12%/−0.39% for instructed/uninstructed motion with Cap-Track pose estimates, with a tracking interval of 1561 ms and high similarity to interleaved navigator estimates (mean absolute difference: [0.13 0.33 0.12] mm, [0.28 0.15 0.22] degrees). Conclusion:Motion can be estimated from recordings of gradient switching with little or no sequence modification, optionally in real time at low computational burden and synchronized to image acquisition, using EEG equipment already found at many research institutions.
Purpose Accuracy investigation of volumetric navigators for motion correction, with emphasis on geometric EPI distortions at ultrahigh field. Methods High‐resolution Dixon images were collected in different head positions and reconstructed to water, fat, T2*, and B0 maps. Resolution reduction was performed, and the T2* and B0 maps were used to apply effects of TE and EPI distortions to simulate various volumetric water and fat navigators. Registrations of the simulated navigators were compared with registrations of the original high‐resolution images. Results Increased accuracy was observed with increased spatial resolution for non‐EPI navigators. When using EPI, the distortions had a negative effect on registration accuracy, which was most noticeable for high‐resolution navigators. Parallel imaging helped to alleviate those caveats to a certain extent, and 5‐fold acceleration gave close to similar accuracy to non‐EPI in most cases. Shortening the TE by partial Fourier sampling was shown to be mostly beneficial, except for water navigators with long readout durations. The EPI blip direction had an influence on navigator accuracy, and positive blip gradient polarities (yielding mostly image stretching frontally) typically gave the best accuracy for water navigators, whereas no clear recommendation could be made for fat navigators. Generally, fat EPI navigators had lower accuracy than water EPI navigators with otherwise similar parameters. Conclusions Echo planar imaging has been widely used for MRI navigators, but the induced distortions reduce navigator accuracy at ultrahigh field. This study can help protocol optimization and guide the complex tradeoff between resolution and EPI acceleration in navigator parameter setup.
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