AND R. S. WOLFE. Role of butyryl phosphate in the energy metabolism of Clostridium tetanomorphum. J. Bacteriol. 86:112-117. 1963.-A partially purified butyrokinase from Clostridium tetanomorphum has been found to phosphorylate valerate, butyrate, isobutyrate, and propionate. The divalent cation requirement is satisfied with magnesium. The pH optimum lies between 7.4 and 8.3. Growth of the organism was followed using glutamate or histidine as substrate, butyrokinase being formed in each instance. The average dry weight of cells formed per mmole of substrate utilized was 6.8 mg for glutamate and 11.1 mg for histidine. Since both phosphotransbutyrylase

All enzymes of the tryptophan synthetic pathway were detectable in extracts from wild-type Acinetobacter calco-aceticus. The levels of these enzymes were determined in extracts from a number of auxotrophs grown under limiting tryptophan. In each case only anthranilate synthetase was found to be present in increased amounts, whereas the specific activities of the remaining enzymes remained unchanged and unaffected by the tryptophan concentration. Derepression of anthranilate synthetase was found to occur as the concentration of tryptophan became limiting. Anthranilate synthetase and phosphoribosyl transferase activities are both feedback-inhibited by tryptophan. Molecular weight determination carried out by gel filtration and zonal centrifugation in sucrose revealed that all the enzymes are less than 100,000, and no molecular aggregates of these enzymes were detected. The data indicate that tryptophan synthesis in Acinetobacter is regulated both by feedback inhibition of the first two enzymes of the pathway and by repression control of anthranilate synthetase. An increasing number of reports have appeared in recent years concerning studies on the tryptophan biosynthetic enzymes from bacterial species outside the enteric group. In the latter, these enzymes are all derepressed under conditions of limiting tryptphan (3, 17, 19). However, the enzymes are not all synthesized coordinately (3). Variations in this pattern of regulation have been observed in Chromobacter violaceum (29) and Pseudomonas putida (6). The levels of the tryptophan enzymes in C. violaceum are unaffected by the tryptophan concentration (29). In P. putida, three enzymes, the first, second, and fourth, respond to changes in the concentration of tryptophan, whereas the level of the third enzyme remains unchanged and the last enzyme, tryptophan synthetase (EC 4.2.1.20), is induced by its substrate indoleglycerol phosphate (6). In all the cases, trptophan feedback inhibits the first enzyme of the pathway, anthranilate synthetase.

Experiments concerned with the regulation of the tryptophan synthetic enzymes in anaerobes were carried out with a strain of Clostridium butyricum. Enzyme activities for four of the five synthetic reactions were readily detected in wild-type cells grown in minimal medium. The enzymes mediating reactions 3, 4, and 5 were derepressed 4to 20-fold, and the data suggest that these enzymes are coordinately controlled in this anaerobe. The first enzyme of the pathway, anthranilate synthetase, could be derepressed approximately 90-fold under these conditions, suggesting that this enzyme is semicoordinately controlled. Mutants resistant to 5-methyl tryptophan were isolated, and two of these were selected for further analysis. Both mutants retained high constitutive levels of the tryptophan synthetic enzymes even in the presence of repressing concentrations of tryptophan. The anthranilate synthetase from one mutant was more sensitive to feedback inhibition by tryptophan than the enzyme from wild-type cells. The enzyme from the second mutant was comparatively resistant to feedback inhibition by tryptophan. Neither strain excreted tryptophan into the culture fluid. Tryptophan inhibits anthranilate synthetase from wild-type cells noncompetitively with respect to chorismate and uncompetitively with respect to glutamine. The Michaelis constants calculated for chorismate and glutamine are 7.6 x 10-5 M and 6.7 x 10-4 M, respectively. The molecular weights of the enzymes estimated by zonal centrifugation in sucrose and by gel filtration ranged from 24,000 to 89,000. With the possible exception of a tryptophan synthetase complex, there was no evidence for the existence of other enzyme aggregates. The data indicate that tryptophan synthesis is regulated by repression control of the relevant enzymes and by feedback inhibition of anthranilate synthetase. That this enzyme system more closely resembles that found in Bacillus than that found in enteric bacteria is discussed.

Objective:To assess the degree to which information retrieved from a biomedical database can augment personal knowledge in addressing novel problems, and how the ability to retrieve information evolves over time.Design: This longitudinal study comprised three assessments of two cohorts of medical students. The first assessment occurred just before student course experience in bacteriology, the second occurred just after the course, and the third occurred five months later. At each assessment, the students were initially given a set of bacteriology problems to solve using their personal knowledge only. Each student was then reassigned a sample of problems he or she had answered incorrectly, to work again with assistance from a database containing information about bacteria and bacteriologic concepts. The initial pass through the problems generated a "personal knowledge"score; the second pass generated a "database-assisted" score for each student at each assessment.Results: Over two cohorts, students' personal knowledge scores were very low (-12%) at the first assessment. They rose substantially at the second assessment (-48%) but decreased six months later (-25%). By contrast, database-assisted scores rose linearly: from -44% at the first assessment to -57% at the second assessment, to -75% at the third assessment.Conclusion: The persistent increase in database-assisted scores, even when personal knowledge had attenuated, was the most remarkable finding of this study. While some of the increase may be attributed to artifacts of the design, the pattern seems to result from the retained ability to recognize problem-relevant information in a database even when it cannot be recalled.n J Am Med Informatics Assoc. 1994;1:328-338.Affiliations of the authors: Laboratory for Computing and Cognition, Office