The biosynthetic route of the pyrimidine moiety of thiamin is different in prokaryotes and eukaryotes. In prokaryotes, the pyrimidine moiety is synthesized from aminoimidazole ribonucleotide, an intermediate of purine biosynthesis, while in eukaryotes, we have reported that the N-1, C-2, and N-3 atoms of the imidazole ring of histidine are incorporated into N-3, C-4, and the amino group attached to the C-4 atoms of the pyrimidine moiety, respectively, as a unit; the rest of the atoms of the pyrimidine moiety originate from pyridoxine as a unit. It has been reported that urocanic acid, the deaminated compound of histidine, is the direct precursor of the pyrimidine moiety. In the present report, we have investigated whether histidine or urocanic acid is the direct precursor of the pyrimidine moiety in Saccharomyces cerevisiae , using tracer experiments with 1) 13 C-formate and urocanic acid, 2) 15 N-NH 4 Cl and urocanic acid, 3) 15 N-NH 4 Cl and histidine, and 4) 13 C-histidine and urocanic acid. The GC-MS analysis revealed that the incorporation of the 15 N atom of 15 NH 4 Cl was not affected by the presence of urocanic acid, although it was affected by histidine, and the incorporation of 13 C-histidine was not affected by the presence of urocanic acid. These results confirm that histidine is the direct precursor of the pyrimidine moiety of thiamin in S. cerevisiae .

Summary It is well known that some amino acids inhibit bacterial growth. L -Serine is known to inhibit the growth of Escherichia coli by inhibition of homoserine dehydrogenase (EC 1.1.1.3). It has been reported that this L -serine inhibition may be prevented by the addition of L -isoleucine or L -threonine to the medium. In our study, however, recovery of the growth inhibition of Escherichia coli by L -serine occurred in the presence of several amino acids, especially L -phenylalanine. In an attempt to further elucidate this inhibition mechanism, different intermediates of aromatic amino acid biosynthesis were added to the growth medium. Recovery from the inhibition did not occur in the presence of prephenate but did occur when phenylpyruvate was added to the medium. The specific activity of prephenate dehydratase decreased in cells grown in the presence of L -serine. However, L -serine did not inhibit in vitro prephenate dehydratase activity, and the expression of pheA, which encodes the prephenate dehydratase, was not depressed by L -serine. We suggest that L -serine acts via another inhibition mechanism. Although this inhibition mechanism has not been fully elucidated, our results suggest that the addition of L -serine to the growth medium inhibits prephenate dehydratase synthesis and thus affects L -phenylalanine biosynthesis.

SummaryThe amide nitrogen atom of glutamine is incorporated into pyridoxine in four eukaryotes (i.e., Emericella nidulans, Mucor racemosus, Neurospora crassa and Saccharomyces cerevisiae) and two prokaryotes (i.e., Staphylococcus aureus and Bacillus subtilis). However, in the prokaryotes Pseudomonas putida, Enterobacter aerogenes and Escherichia coli, it is the ni trogen atom of glutamate that is incorporated into pyridoxine (J Nutr Sci Vitaminol (2000) 46, 55-57). As these results were from experiments conducted under aerobic conditions, we investigated the biosynthesis of pyridoxine on S. cerevisiae under anaerobic conditions. The results showed that [amide-15N]L-glutamine was not incorporated into pyridoxine, un like the results for aerobic conditions. The incorporation of [15N]ammonium salts into pyri doxine was not inhibited in the presence of casamino acids and tryptophan. The results showed that the nitrogen atoms of amino acids are not used for the biosynthesis of pyridox ine. The incorporation of 15N into pyridoxine was inhibited in the presence of adenine, but not in that of hypoxanthine. Thus, the nitrogen atom of pyridoxine may be from the amino group attached to the C-6 of adenine.

Background: Faulty cleaning of surgical instruments may lead to corrosion damage and a higher risk of surgical site infection. We have developed a method in which each instrument has an attached radiofrequency identification (RFID) tag for individual management. However, because of the structure of the instruments, a risk of corrosion from poor cleaning exists; therefore, observation during long-term usage is necessary.Methods: The cleaning effect at the jig of the RFID tag was verified by the amount of residual protein left by various cleaning methods. In our investigation of long-term usage, we examined 94 surgical instruments with RFID tags used in the operating room for 50 months employing a microscope to identify any corrosion at the jig.Results: The method using a washer disinfector (WD) was found to be highly effective. From observation after long-term usage, friction by the RFID tag occurred in about 70% of the jigs. However, no pitting or general corrosion was seen.Conclusions: When WD is used properly, there is only a minor risk of residual protein, and corrosion does not occur even with long-term use. By using surgical instruments with RFID tags, it is possible to determine the number of uses and the history at the individual level. This facilitates operation of safe surgical instruments by limiting the number of times a particular instrument is used.