Evidence for Cu(I) clusters and Zn(II) clusters in neuronal growth-inhibitory factor isolated from bovine brain

etallothionein. By analogy with Cu 8 -metallothionein, we propose the presence of a Cu 4 cluster with similar electronic structure in native GIF. However, the determined Cys/Cu 1 ratio of approximately 2 : 1 in Cu, Zn-GIF is higher than the ratio found in mammalian Cu(I)-metallothionein forms (approximately 1.6 : 1), which implies that the coordination geometry of Cu 1 -binding sites is different in the Cu 4 cluster. The spectroscopic characterization of Zn 21 -substituted and Cd 21 -substituted GIF (627 metal ions/protein) showed CD and MCD features at positions identical to those reported for the well-characterized mammalian Zn 7 -metallothionein and Cd 7 -metallothionein. Therefore, it is inferred that the cluster organization in GIF with divalen