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The study of interactions between FAD - flavin adenine dinucleotide and histidine

Sabara D.

Zeszyty Naukowe. Chemia Spożywcza i Biotechnologia / Politechnika Łódzka

2008

Z. 72

63-71

In view of the fact that one of the amino acids, histidine, performs an important role in the interactions with flavin adenine dinucleotide (FAD) in the catalytic center of glucose oxidase (GOD), we performed an investigation if interactions between FAD and histidine. The theoretical approach indicates the stacked conformation of FAD, in which the isoalloxazine and adenine ring couple with each other, and an extended - unstacked conformation. Formation of the complex was studied using fluorescence method and computer modeling in order to define the geometrical parameters of the hydrogen bond formation by means of the semi-empirical method (AM1, PM3). The possible distances, angles and stretch vibrations were supported by fluorescence lifetime decay and the Gibbs free energy of the complex.

W pracy opisano badania oddziaływań pomiędzy dinukleotydem flawinoadeninowym a histydyną. Jeden z aminokwasów - histydyna odgrywa ważną rolę w oddziaływaniu z dinukleotydem flawinoadeninowym znajdującym się w centrum aktywnym oksydazy glukozowej (GOD). Teoria potwierdza istnienie dwóch konformacji dinukleotydu flawinoadeninowego; zamkniętej, w której pierścienie adeninowy i izoaloksazynowy reagują ze sobą oraz otwartej - liniowej. Tworzenie kompleksu pomiędzy FAD a histydyną zbadano metodami fluorescencyjnymi oraz przy użyciu optymalizacji komputerowej w celu zdefiniowania parametrów wiązania wodorowego (AM1, PM3). Określenie możliwych interakcji i konfiguracji molekuł zostało wsparte fluorescencyjnymi pomiarami czasów życia oraz wyliczeniem energii Gibbsa powstałego kompleksu.

Behaviour of glucose oxidase during formation and ageing of silica gel studied by fluorescence spectroscopy

Przybyt M.

Materials Science

2003

Vol. 21, No. 4

397-416

Glucose oxidase was entrapped in silica gels obtained by the sol-gel process with the retention of a part of its activity. The stability of the enzyme molecule during the sol-gel transition and ageing of the wet gel was followed by the measurement of fluorescence of tryptophan and flavin adeninedinucleotide (FAD). The results indicate unfolding and denaturation of the enzyme protein caused by the changes of microenvironment inside gel, presence of ethanol, decomposition of FAD and photosensitised oxidation of tryptophan by FAD. Among the products of FAD decomposition, alloxazine derivatives were identified through their specific fluorescence characteristics. The results of the observation of the fluorescencje variation and activity assay of the gel are in good agreement. The experiments with the dried gel indicato that illumination is not necessary to sensitise the reaction of oxidation of tryptophane by FAD although In the presence of light the effectiveness of this process is higher. Presumably the decomposition of FAD and tryptophan is not only induced by light but also by the paramagnetic (with free radical character) defects in the gel matrix. This reaction is enhanced by the presence of glucose and depends also on pH of the buffer used in the gel preparation. The products of the enzyme degradation are easily washed out from the gel. Leaching of active enzyme from the gel was also observed.