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Volume 68, Issue 1
Displaying 1-7 of 7 articles from this issue
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Retsu MlUIRAArticle type: Article
1994 Volume 68 Issue 1 Pages 1-13
Published: January 25, 1994
Released on J-STAGE: March 30, 2018
JOURNAL OPEN ACCESSFlavocoenzymes are extremely versatile but the reaction catalyzed by each individual flavoenzyme is highly specific. This requires the prerequisite mechanism that controls the flavin reactivity. In order to understand this control mechanism, the author has investigated various flavoenzymes focusing on how the flavin reactivity is controlled by monitoring the electronic state of the flavin moiety and its fluctuation along the reaction pathway. In the present report, two flavoenzymes, _D-amino acid oxidase and medium-chain acyl-CoA dehydrogenase, are concerned, the major method being ^<13>C- and ^<15>N-NMR spectroscopy of these enzymes reconstituted with ^<13>C- and ^<15>N-enriched FAD. The results obtained indicate the following : 1. The reactivity of flavin in the oxidized form of the enzymes is controlled by hydrogen-bonding network in the protein matrix and by its fluctuation during the reaction sequence. 2. In the control of the flavin reactivity, the overlap between LUMO (lowest unoccupied molecular orbital) of flavin and HOMO (highest occupied molecular orbital) of the substrate plays an important role. 3. The reoxidation process of the reduced enzymes is controlled by modulation of the electron density at C (4a) of reduced flavin, this position being the site of nucleophilic attack to molecular oxygen.Flavocoenzymes are extremely versatile but the reaction catalyzed by each individual flavoenzyme is highly specific. This requires the prerequisite mechanism that controls the flavin reactivity. In order to understand this control mechanism, the author has investigated various flavoenzymes focusing on how the flavin reactivity is controlled by monitoring the electronic state of the flavin moiety and its fluctuation along the reaction pathway. In the present report, two flavoenzymes, _D-amino acid oxidase and medium-chain acyl-CoA dehydrogenase, are concerned, the major method being ^<13>C- and ^<15>N-NMR spectroscopy of these enzymes reconstituted with ^<13>C- and ^<15>N-enriched FAD. The results obtained indicate the following : 1. The reactivity of flavin in the oxidized form of the enzymes is controlled by hydrogen-bonding network in the protein matrix and by its fluctuation during the reaction sequence. 2. In the control of the flavin reactivity, the overlap between LUMO (lowest unoccupied molecular orbital) of flavin and HOMO (highest occupied molecular orbital) of the substrate plays an important role. 3. The reoxidation process of the reduced enzymes is controlled by modulation of the electron density at C (4a) of reduced flavin, this position being the site of nucleophilic attack to molecular oxygen.View full abstractDownload PDF (1077K) -
Masato SHIMIZU, Sachiko YAMADAArticle type: Article
1994 Volume 68 Issue 1 Pages 15-30
Published: January 25, 1994
Released on J-STAGE: March 30, 2018
JOURNAL OPEN ACCESSA new sensitive and highly reactive fluorescence-labeling reagent (DMEQ-TAD) targeting conjugated dienes was developed. The fluorescent dienophile (DMEQ-TAD), in which fluorescent dimethoxyquinoxalinone (DMEQ) group is substituted via ethylene spacer on a dienophile, 1,2,4-triazoline-3,5-dione (TAD), was synthesized in 8 steps in 24% overall yield from dinitroveratrole. The reactions of DMEQ-TAD with six major vitamin D metabolites and some synthetic analogs were examined under various conditions. The reaction produced the corresponding 6,19-cycloadduct as a pair of the C (6) epimers (8 and 9) in quantitative yield. The structures of the adducts (8 and 9) including the stereochemistry at C (6) were unambiguously determined. The fluorescence-labeled vitamins were analyzed by HPLC with fluorescence detector. The new fluorometric method was used in the assay of plasma 25-OH-D_3, 24,25 (OH)_2D_3, and 25,26 (OH)_2D_3. The method was proved to be precise and reliable by comparing with the HPLC-UV method. The reaction of DMEQ-TAD with vitamin A metabolites and fluorometric assay of plasma retinoic acid was also examined.View full abstractDownload PDF (1325K) -
Tetsunori KAWATA, Yoshiko IKAWA, Yuka HIROSE, Akiko HAISHA, Akiko FUJI ...Article type: Article
1994 Volume 68 Issue 1 Pages 31-38
Published: January 25, 1994
Released on J-STAGE: March 30, 2018
JOURNAL OPEN ACCESSUtilization of dietary protein in vitamin B_<12> (B_<12>)-deficient rats was evaluated by determination of plasma proteins levels, hepatic xanthine oxidase activity, and urinary excretion of nitrogen compounds after the rats had been fed on the B_<12>-deficient soy bean protein diet for 90 days. It was confirmed that the rats was extremely B_<12>-deficient for distinct increase in urinary methylmalonic acid and marked decrease in hepatic B_<12> contents. Growth of the B_<12>-deficient rats was significantly retarded as compared with the ad libitum-feeding control rats and the pair-feeding control rats. Plasma total protein and albumin levels in rats fed on the B_<12>-deficient diet decreased, compared with the pair-feeding control, although the increase in urea-nitrogen was observed. And the decrease of hepatic xanthine oxidase activity was observed in the B_<12>-deficient rats. The excretion of urinary nitrogen compounds, such as urea-nitrogen, allantoin, and creatinine, were all significantly decreased by B_<12>-deficiency compared with the pair-feeding control. The above results suggested that extreme B_<12>-deficiency depressed the utilization of dietary protein in rats. Moreover, adaptation to decrease of dietary protein utilization due to the B_<12>-deficiency was possibly supposed.View full abstractDownload PDF (809K) -
Article type: Appendix
1994 Volume 68 Issue 1 Pages 39-43
Published: January 25, 1994
Released on J-STAGE: March 30, 2018
JOURNAL OPEN ACCESSDownload PDF (436K) -
[in Japanese]Article type: Article
1994 Volume 68 Issue 1 Pages 45-46
Published: January 25, 1994
Released on J-STAGE: March 30, 2018
JOURNAL OPEN ACCESSDownload PDF (320K) -
[in Japanese]Article type: Article
1994 Volume 68 Issue 1 Pages 46-47
Published: January 25, 1994
Released on J-STAGE: March 30, 2018
JOURNAL OPEN ACCESSDownload PDF (308K) -
[in Japanese]Article type: Article
1994 Volume 68 Issue 1 Pages 47-49
Published: January 25, 1994
Released on J-STAGE: March 30, 2018
JOURNAL OPEN ACCESSDownload PDF (323K)
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