Ribonucleotide reductase is an iron-containing enzyme that is essential for DNA synthesis. Whereas previous studies have used various iron chelators to examine the relationship between cellular iron metabolism and ribonucleotide reductase activity in cells, they have not elucidated the relationship between iron transport into cells and the expression of the gene for ribonucleotide reductase. To...

It is shown by analysis of a cyclic enzymatic network that the presence zero net flux/current cycles impose strong thermodynamic constraints on values kinetic parameters. Thermodynamic carried out for four-node pyramidal reaction involving conversion 7,8-­dihydrofolate (H2F) and NADPH in H+ to 5,6,7,8-­tetrahydrofolate (H4F) NADP+ catalyzed universal enzyme dihydrofolate reductase (DHFR). The c...

The problem of the low activity of so-called methemoglobin reductase in red cells from newborns was reinvestigated in view of our current knowledge of this enzyme, i.e., (1) its being cytochrome-b5 reductase and (2) its presence in two forms: soluble and membrane-bound. We found that red cells from cord blood and newborns exhibited a 50% decrease of soluble cytochrome-b5 reductase activity, whe...

(6R)-2,2,6-Trimethyl-1,4-cyclohexanedione (levodione) reductase was isolated from a cell extract of the soil isolate Corynebacterium aquaticum M-13. This enzyme catalyzed regio- and stereoselective reduction of levodione to (4R,6R)-4-hydroxy-2,2, 6-trimethylcyclohexanone (actinol). The relative molecular mass of the enzyme was estimated to be 142,000 Da by high-performance gel permeation chroma...

Nitrate reductase was found in leaves of apricot Prunus armeniaca, sour cherry P. cerasus, sweet cherry P. avium, and plum P. domestica, but not in peach P. persica, from trees grown in sand culture receiving a nitrate containing nutrient solution. Nitrate was found in the leaves of all species. Nitrate and nitrate reductase were found in leaves of field-grown apricot, sour cherry, and plum tre...

THE INDUCTION AND REINDUCTION OF NITRATE REDUCTASE IN ROOT TIP OR MATURE ROOT SECTIONS SHOW ESSENTIALLY A SIMILAR PATTERN: a lag, a period of rapid increase in enzyme activity and finally a period of relatively minor change. Both inductions are sensitive to 6-methylpurine and cycloheximide. Kinetic studies with 6-methylpurine suggest that the half-life of the messenger RNA for nitrate reductase...

The results of previous work have indicated (2, 3) that one sulfhydryl group of microsomal cytochrome reductase is essential for the interaction of nucleotides with this enzyme. These results, however, do not rule out the possibility that there are other reactive sulfhydryl groups on the native enzyme and that they are involved directly or indirectly in nucleotide-enzyme interactions. In the ex...

Prostaglandin 9-ketoreductase has been purified to apparent homogeneity from pig and human kidney with an overall yield of 6%. The enzyme has a molecular mass of 34 kDa, it is present as an active monomer in diluted solution and contains approx. 2 equivalents Zn++/mole enzyme. It is stereoselective for the pro(S) hydrogen of NADPH and reduces the prostaglandin 9-keto group to yield 90% prostagl...

The intracellular localization of the post-translationally inserted integral membrane protein, NADH-cytochrome b5 reductase, was investigated, using a quantitative radioimmunoblotting method to determine its concentration in rat liver subcellular fractions. Subcellular fractions enriched in rough or smooth microsomes, Golgi, lysosomes, plasma membrane and mitochondrial inner or outer membranes ...

The assimilation of nitrate in plants involves the reduction of nitrate to ammonia in two steps. The first step requires nitrate reductase, a nitrate-inducible enzyme. When seedlings of squash (Cucurbita maxima L.) were treated with nitrate, both nitrate reductase activity and protein were induced in the cotyledons. Poly(A)(+) RNA was prepared from cotyledons of nitrate-treated seedlings and wa...