Isoalloxazine nucleus

The isoalloxazine nucleus of the flavins [3-(R or H)-7,8-dimethyl-lO-R -isoalloxazines] may exist in the fully reduced (1,5-di-hydro-), the radical (semiquinone), and the fully oxidized (quinone) states. Because of acid-base equilibria, each of these oxidation states... 

The intrinsic chemical properties of the isoalloxazine nucleus, as modulated by the protein environment, are at the heart of the success of flavoenzymes in nature. The chemical versatility... 

Insofar as the flavin complexes are concerned, the work in this field may be summarized as follows. About ten years ago, Theorell and Nygaard proposed a scheme for the binding of FMN to the old yellow enzyme which envisioned hydrogen bonding at the isoalloxazine nucleus, as in Fig. 18. Tyrosine was implicated at the binding site by iodination studies. 

In the following we consider some of the more recent reports of complexes involving riboflavin. Fleishman and Tollin have attempted to determine whether the acceptor strength of riboflavin can be increased by protonation of the isoalloxazine nucleus. They report complex formation between a number of phenols and riboflavin, and a few with lumiflavin and lumichrome, in 6-12 N acid (entries 27-42, Table II). In some cases highly colored com-... 

Riboflavin (vitamin B2) consists of a dimethyl-isoalloxazine nucleus combined with ribitol. Its structure is shown here ... 

The basis of the yellow green riboflavin structure (vitamin Bj, formerly also known as vitamin G, lactoflavin, ovoflavin or uroflavin) is an isoalloxazine nucleus, to which is bound the alditol ribitol at position N-10 (5-58). Riboflavin exists in an oxidised (flavo-quinone) and a reduced form (flavohydroquinone). 

The first SERRS spectra reported for GO at Ag surfaces were similar to spectra reported for free FAD adsorbed at Ag colloids and at Ag electrodes (Figure 1). The spectral resemblance was initially ascribed to an interaction between the protein-bound FAD and the Ag surface which is similar,to that of free flavin The plausibility of this interpretation was supported by previously published results indicating that the ring III portion of the flavin isoalloxazine (shown below) nucleus is accessible to... 

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