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The crystal structure of adenosine deaminase (ADA) from bovine intestine complexed with a transition-state analogue, 6-hydroxy-1,6-dihydropurine riboside (HDPR), was solved at 2.5 A resolution by the molecular-replacement method using a homology model based on the crystal structure of mouse ADA. The final refinement converged to a crystallographic R factor of 20.7%. The C(alpha) backbone of bovine ADA is mostly superimposable on that of mouse ADA, although mouse ADA itself did not lead to a solution by molecular replacement. HDPR tightly interacts with ADA by means of six hydrogen bonds and is entirely enclosed within the active site. The lid of the envelope consists of two components: one contains two leucine residues, Leu55 and Leu59, and the other contains the backbone atoms Asp182 and Glu183. The C(delta) atoms of the two leucine residues are 3.5 A from the respective N atoms of the backbone. A weak interaction, similar to CH-pi binding, might make it possible to open the lid. Taking account of the movement and observation of this structural feature, the aim is to design novel ADA inhibitors.

The crystal structure of plastocyanin from a green alga, Ulva pertusa, has been determined at 1.6-Å resolution. At its copper site, U. pertusa plastocyanin has a distorted tetrahedral coordination geometry similar to other plastocyanins. ) bond of poplar and C. reinhardtii plastocyanins by 0.14 and 0.20 Å, respectively. As a result of structural differences, U. pertusa plastocyanin has a less distorted geometry than the other plastocyanins. Thus, the cupric geometry is finely tuned by the interactions between residues 85 and 88 and between residues 83 and 88. This result implies that the copper site is more flexible than reported formerly and that the rack mechanism would be preferable to the entatic theory. The HisMet loop may regulate the electron transfer rate within the complex between plastocyanin and cytochrome f.

The single type 1 copper protein pseudoazurin from Achromobacter cycloclastes gives reversible electrochemical behavior at a (4-pyridyl)disulfide-modified gold electrode. Measurements carried out at 25.0°C indicate a midpoint reduction potential of E1 ⁄2 ‫؍‬ 260 mV versus normal hydrogen electrode at pH 7.0 and a peakto-peak separation of ⌬E p ‫؍‬ 59 mV. The diffusion coefficient and heterogeneous electron transfer rate constant are estimated to be 2.23 ؋ 10 ؊6 cm 2 s ؊1 and 3.7 ؋ 10 ؊2 cm s ؊1 , respectively. Also, controlled potential electrolysis indicates a 1-electron transfer process and a formal reduction potential of 259 mV versus normal hydrogen electrode for the Cu(II)/Cu(I) couple. The heterogeneous electron transfer rate constant determined at the (4-pyridyl)disulfide-modified gold electrode at pH 4.6 is 6.7 ؋ 10 ؊3 cm s ؊1, consistent with a slower process at the positively charged electrode surface. At pH 11.3, UVvisible, EPR, and resonance Raman spectra indicate a conversion of the distorted tetrahedral copper geometry to a trigonal structure. The trigonal form has elongated axial bonding and an axial EPR spectrum. At pH 11.3, the reduction potential is further decreased, and Cu-S bands in resonance Raman spectra at 330 -460 cm ؊1 are shifted to higher energy (ϳ10 cm ؊1

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