Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.4.21.4 (trypsin)
 42,187 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Dehydroascorbate reductase has been isolated from spinach chloroplasts and purified to apparent homogeneity. The N-terminal amino acid sequence of the enzyme is homologous to the Kunitz-type trypsin inhibitors from plant sources. It is shown that spinach DHA reductase and soybean trypsin inhibitor are both capable of reducing dehydroascorbate when in the reduced (thiol) form but acquire trypsin-inhibiting activity in the oxidized (disulfide) state. Reduced chloroplast thioredoxins also reduce dehydroascorbate.
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PMID:A novel-dehydroascorbate reductase from spinach chloroplasts homologous to plant trypsin inhibitor. 792 67

Ocular tissues appear to require high levels of ascorbic acid and the elucidation of the mechanisms by which those tissues maintain the vitamin in its reduced state remains an important objective. The regeneration of ascorbate from its oxidative by-product, dehydroascorbic acid (DHAA), was studied in bovine iris-ciliary body. Iris-ciliary body was removed by scalpel, weighed, minced, and homogenized in 20 mM MOPS, 62 mM sucrose, and 0.1 mM EDTA at pH 7.0. The homogenate was centrifuged and precipitated with ammonium sulfate such that maximal DHAA reducing activity was enhanced in a 50-75% ammonium sulfate fraction. This fraction was employed for subsequent characterization of DHAA reduction by iris-ciliary body. Results indicate that the iris-ciliary body enzymatically reduces DHAA to ascorbate at a rate significantly greater than can be accounted for by a nonenzymatic glutathione-dependent mechanism. In addition, saturation kinetics are observed, and the enzymatic activity is dependent on protein concentration, DHAA concentration, and reduced glutathione (GSH) concentration. The activity is sensitive to pH, to high temperature, and to digestion by trypsin and is greatest in the presence of both GSH and NADPH. The reducing activity is therefore attributed to one or more proteins that are distinct from the known ascorbate regenerating enzyme, GSH-dependent DHAA reductase (EC 1.8.5.1).
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PMID:Ascorbic acid regeneration by bovine iris-ciliary body. 822 19

In many physiological studies dehydroascorbate (DHA) reductase is regarded as one of the chloroplast enzymes involved in the protection against oxidative stress. Here, evidence is presented that plant cells do not possess a specific DHA reductase. The DHA reductase activities measured in plant extracts are due to side reactions of proteins containing redox-active dicysteine sites. Native gel electrophoresis combined with specific activity staining revealed three different proteins with DHA reductase activity in leaf and chloroplast extracts. These proteins have been identified as thioredoxins and trypsin inhibitors (Kunitz type) by Western blot analysis. The essential regulatory functions of thioredoxins in chloroplast metabolism are strongly inhibited in the presence of as little as 50 microM DHA. Thus, the intracellular DHA concentration should be kept below 50 microM but not all proteins with DHA reductase activity are effective enough for this purpose. A specific DHA reductase is frequently demanded as part of the enzymatic equipment to avoid oxidative stress. We argue that this is not necessary because in chloroplasts DHA does not accumulate to any significant extent due to the high activities of monodehydroascorbate reductase and of reduced ferredoxin.
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PMID:Dehydroascorbate and dehydroascorbate reductase are phantom indicators of oxidative stress in plants. 932 37

A complex containing trypsin inhibitor (TI) activity was extracted with 0.1 M TRIS buffer (pH 7.9) from trypsin-treated mitochondria of etiolated mung bean seedlings, and further purified with a Superdex 200 FPLC column. This partially purified complex with an M(r) about 820 kDa exhibited additional dehydroascorbate (DHA) reductase activity with specific activities of 0.21, 1.53 and 1.54 mumol ascorbate formed min-1 mg-1 protein at pH 6.0, 6.5 and 7.0, respectively, when glutathione was added. Much lower DHA reductase activity (0.013 and 0.026 mumol ascorbate formed min-1 mg-1 protein at pH 6.5 and 7.0, respectively) was found when glutathione was omitted. The isolated complex gave positive results when it was tested by TI activity staining after SDS-PAGE, and could be recognized by a polyclonal antibody which was raised against 38 kDa sweet potato Kunitz-type TI, one of the root storage proteins of sweet potato. The possible physiological functions of this complex with both TI and DHA reductase activities were discussed.
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PMID:A complex containing both trypsin inhibitor and dehydroascorbate reductase activities isolated from mitochondria of etiolated mung bean (Vigna radiata L. (Wilczek) cv. Tainan no. 5) seedlings. 1093 63

A cDNA encoding a small cysteine-rich protein designated defensin (SPD1) was isolated from sweet potato storage roots. On the basis of the amino acid sequence similarity and conserved residues, it is suggested that SPD1 is a member of the plant defensin family. Recombinant SPD1 protein overproduced in Escherichia coli was purified by Ni (2+)-chelated affinity chromatography. A recombinant protein from the storage root cDNA clone effectively inhibited the trypsin activity in a dose-dependent manner. Both the corresponding mRNA and protein level were found to be highest in the storage roots, followed by sprout. SPD1 reduced dehydroascorbate (DHA) in the presence of glutathione to regenerate l-ascorbic acid (AsA). However, without glutathione, SPD1 has very low DHA reductase activity, and AsA was oxidized by AsA oxidase to generate monodehydroascorbate (MDA) free radical. MDA was also reduced by SPD1 to AsA in the presence of NADH, mimicking the MDA reductase catalyzed reaction. These data suggest that SPD1 has both DHA reductase and MDA reductase activities. SPD1 was also shown to inhibit the growth of both fungi and bacteria. SPD1 is apparently the first reported plant defensin exhibiting DHA and MDA activities in vitro.
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PMID:Antimicrobial, dehydroascorbate reductase, and monodehydroascorbate reductase activities of defensin from sweet potato [Ipomoea batatas (L.) Lam. 'Tainong 57'] storage roots. 1839 37