The putative glycine dehydrogenase of Mycobacterium tuberculosis catalyzes the reductive amination of glyoxylate to glycine but not the reverse reaction. The enzyme was purified and identified as the previously characterized alanine dehydrogenase. The Ald enzyme was expressed in Escherichia coli and had both pyruvate and glyoxylate aminating activities. The gene, ald, was inactivated in M. tuberculosis, which resulted in the loss of all activities. Both enzyme activities were found associated with the cell and were not detected in the extracellular filtrate. By using an anti-Ald antibody, the protein was localized to the cell membrane, with a smaller fraction in the cytosol. None was detected in the extracellular medium. The ald knockout strain grew without alanine or glycine and was able to utilize glycine but not alanine as a nitrogen source. Transcription of ald was induced when alanine was the sole nitrogen source, and higher levels of Ald enzyme were measured. Ald is proposed to have several functions, including ammonium incorporation and alanine breakdown. Mycobacterium tuberculosis is the causative agent of tuberculosis, and one of the most successful human pathogens. It was responsible for approximately 2 million deaths in 2008, while currently almost one-third of the world's population is infected with this organism. Research with M. tuberculosis has described a pathogen uniquely adapted to the wide range of harsh environments presented by the host. Much of this work has focused on the microbe's metabolism, with the idea of identification of novel enzymes or pathways to target for drug development.One of these environmental factors is nitrogen availability. Very little is known about the nitrogen sources used by M. tuberculosis in vivo. M. tuberculosis can utilize many amino acids for nitrogen, including alanine and glycine (29). Mutants of M. tuberculosis unable to synthesize proline retained the ability to replicate in the human macrophage cell line THP-1 (35), while other amino acid auxotroph mutants were attenuated (3,17,22,52). A Mycobacterium bovis BCG mutant unable to make methionine showed survival in mice similar to the wild-type strain (32). This suggests some amino acids are available in vivo and serve as nutrients for M. tuberculosis.The enzyme glycine dehydrogenase was first described in M. tuberculosis in 1962 (16). This enzyme was detected by the reductive amination of glyoxylate to glycine concurrent with the oxidation of NADH to NAD ϩ (Fig. 1). This reaction represents glyoxylate reductive aminase (GxRA) activity. The activity corresponding to the reverse reaction, catalyzed by glycine dehydrogenase (GDH), was not detected. The expression of glyoxylate reductive amination by a putative glycine dehydrogenase in M. tuberculosis has been characterized in nonreplicating persistent (NRP) cultures (58). In the Wayne model of dormancy, sealed cultures of M. tuberculosis create a microaerobic environment (NRP-1), which subsequently develops into the anaerobic stage (NRP-2) (58). GxRA activity w...

Both Mycobacterium tuberculosis and Mycobacterium bovis can produce tuberculosis in humans. Mycobacterium tuberculosis has low nitrate reductase activity during aerobic growth (AG), but shows strong hypoxic induction. Virulent M. bovis has weak activity during AG with no hypoxic induction. Bacille Calmette-Guerin (BCG) lacks activity in both stages. Transcription of narG of the nitrate reductase enzyme operon was higher in M. tuberculosis than in M. bovis or BCG. Transcription of narK2 encoding the nitrate transporter was induced by hypoxia in M. tuberculosis but not M. bovis or BCG. Insertion of the M. tuberculosis narGHJI operon into M. bovis resulted in increased activity only during AG. Regulation of both the nitrate reductase enzyme and transporter are regulated differently in the two species.

Background: Psychiatric patients experience longer treatment times (length of stay [LOS]) in the emergency department (ED) compared to nonpsychiatric patients. Although patients on involuntary mental health holds are relatively understudied, common wisdom would hold that times for these patients can only be affected by addressing systems issues because they are not free to leave. The objective of this study was to determine whether both selected ED and patient-specific factors were associated with longer LOS. We hypothesized that nonmodifiable factors (age, sex, agitation, presentation during evenings/nights, presentation during weekends, suicidal ideation) would prolong LOS but that potentially modifiable factors (such as use of medication) would reduce LOS. Methods: A historical cohort of patients (January 1, 2009-August 16, 2010) placed on involuntary mental health holds was studied in 2 general EDs. A regression model was used to calculate the effects of modifiable and nonmodifiable factors on LOS. Results: Six hundred forty patient visits met all inclusion/exclusion criteria. Longer LOSs were significantly associated with suicidal ideation, use of antipsychotics, and use of benzodiazepines, although agitation did not predict longer LOSs. Longer LOSs were also longer with presentation on the weekends. Conclusions: Lengths of stay for patients on involuntary mental health holds are associated with several factors outside the control of the typical ED clinician such as the ability to clear holds quickly due to day of week or placement of the hold for suicidal ideation. Lengths of stay are also increased by factors within the control of the typical ED clinician, such as administration of calming medication.