The methylotroph Methylobacterium extorquens AM1 oxidizes methanol and methylamine to formaldehyde and subsequently to formate, an intermediate that serves as the branch point between assimilation (formation of biomass) and dissimilation (oxidation to CO₂). The oxidation of formaldehyde to formate is dephosphotetrahydromethanopterin (dH₄MPT) dependent, while the assimilation of carbon into biom...

Kiese (1) reported the presence of an enzyme in erythrocytes that would catalyze the reduction of methemoglobin by reduced triphosphopyridine nucleotide in the presence of methylene blue. This enzyme was purified further by Huennekens et al. (2) and reported to be active both with TPNH and, to a lesser extent, with DPNH. It was postulated that this enzyme was responsible for the physiological m...

The glycine cleavage system catalyzes the following reversible reaction: Glycine + H(4)folate + NAD(+) <==> 5,10-methylene-H(4)folate + CO(2) + NH(3) + NADH + H(+)The glycine cleavage system is widely distributed in animals, plants and bacteria and consists of three intrinsic and one common components: those are i) P-protein, a pyridoxal phosphate-containing protein, ii) T-protein, a protein re...

each step being catalyzed by a separate enzyme, El (folic acid reductase) and Et (dihydrofolic acid reductase) (2). The purification of dihydrofolic acid reductase from chicken liver (3) and from sheep liver (4) has been reported. In each case the final preparation reduced only dihydrofolate; no mention was made of the distribution in different fractions of folic acid reductase which was presum...

Yersinia type III machines secrete protein substrates across the bacterial envelope. Secretion signals of some substrates have been identified; however, the mechanisms whereby these signals interact with type III machines are not known. Here we show that fusion of YopR, an early secretion substrate, to the N terminus of dihydrofolate reductase (DHFR) or other tightly folded proteins generates i...

Saccharomyces cerevisiae possess a monofunctional, cytoplasmic NAD-dependent 5,10-methylenetetrahydrofolate (THF) dehydrogenase that converts 5,10-methylene-THF to 5,10-methenyl-THF (Barlowe, C. K., and Appling, D.R. (1990) Biochemistry 29, 7089-7094). We have now isolated the gene encoding this enzyme from a yeast genomic library using oligonucleotide probes based on internal peptide sequences...