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8-Fluoro-8-demethylriboflavin was shown to be a potential active-site-directed reagent for flavoproteins. It reacted with the nucleophiles of N-acetylcysteine (-SH), N-acetyltyrosine (-OH), alpha-N-acetyllysine, and glycine (epsilon- and alpha-NH2, respectively) under fairly mild conditions, and the reaction products were identified. The reactivity of the fluoroflavin was higher than that of 8-chloro-8-demethylriboflavin, which reacted only with the cysteine derivative among the amino acid derivatives used, and whose pseudo first order rate constant at 23 degrees C was 1/23 of that of the fluoroflavin. The reactivity of the fluoroflavin was also estimated by 13C and 19F NMR spectroscopy. The results showed that this compound is more reactive than the chloroflavin.

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A flavoprotein, FP390, obtained from a luminescent bacterium, Photobacterium phosphoreum, in the purification of luciferase has been crystallized by the vapor-diffusion procedure. Crystals obtained from polyethylene glycol 4000 solutions, whose X-ray photographs show powder diffraction patterns, were unsuitable for further crystallographic work. However, tetragonal crystals grown from potassium phosphate solution well diffracted X-rays beyond 3 A resolution. The space group of this crystal is P4(1)22 or P4(3)22 with unit-cell dimensions of a = b = 76.8 and c = 241 A. Assuming two or three molecules in an asymmetric unit, the value for the crystal volume per unit molecular mass, Vm, is calculated as 3.3 or 2.2 A3/Da, respectively. A total of 13,555 independent reflections for the native crystal was collected up to 3 A resolution using a Weissenberg camera attached to the synchrotron radiation source, the merging R factor being 0.077 for 79,335 measurements.

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