The quinone cofactor TPQ in copper amine oxidase is generated by posttranslational modification of an active site tyrosine residue. Using X-ray crystallography, we have probed the copper-dependent autooxidation process of TPQ in the enzyme from Arthrobacter globiformis. Apo enzyme crystals were anaerobically soaked with copper; the structure determined from this crystal provides a view of the initial state: the unmodified tyrosine coordinated to the bound copper. Exposure of the copper-bound crystals to oxygen led to the formation of freeze-trapped intermediates; structural analyses indicate that these intermediates contain dihydroxyphenylalanine quinone and trihydroxyphenylalanine. These are the first visualized intermediates during TPQ biogenesis in copper amine oxidase.

Magnetic properties of the S1-state manganese cluster in the oxygen-evolving photosystem II were studied by parallel polarization electron paramagnetic resonance spectroscopy. Dark minus light spectra gave rise to a broad S1-state signal with a g value of about 4.9 [Dexheimer, S. L., Klein, M. P. (1992) J. Am. Chem. Soc. 114, 2821-2826]. Temperature variation of the signal intensity between 1.9 and 10 K observed in PS II with a sucrose buffer indicates that the signal originates from an excited state with a spin S of 1 with separation from the ground state (S = 0) of about 2.5 K. The S1-state signal was also observed in the sucrose buffer supplemented by 50% glycerol. However, no S1-state signal was detected by addition of 3% methanol or 30% ethylene glycol in the sucrose buffer, although illumination at 200 K in the presence of these alcohols induced the normal multiline S2 signal. Furthermore, modification of the Mn cluster by Cl- or Ca2+ depletion from PS II membranes failed to produce a detectable S1-state signal. A possible magnetic structure of the Mn cluster responsible for the generation of the S1-state signal is discussed on the basis of these observations.

The light-induced new EPR signals at g = 12 and 8 were observed in photosystem II (PS II) membranes by parallel polarization EPR. The signals were generated after two flashes of illumination at room temperature, and the signal intensity had four flashes period oscillation, indicating that the signal origin could be ascribed to the S3-state. Successful simulations were obtained assuming S = 1 spin for the values of the zero-field parameters, D = +/-0.435 +/- 0. 005 cm-1 and E/D = -0.317 +/- 0.002. Orientation dependence of the g =12 and 8 signal intensities shows that the axial direction of the zero-field interaction of the manganese cluster is nearly parallel to the membrane normal.