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.

Three new C21 linear polyacetylenes, callypentayne (1), callyberyne B (2), and callytetrayne (3), along with the known compound siphonodiol (4), have been isolated from the Japanese marine sponge Callyspongia sp. The structures of 1−3 were proposed on the basis of extensive NMR experiments.