S. Capasso

tert-Butyloxycarbonyl-l-aminosuccinyl-glycyl-l-alanine methyl ester (Boc-l-Asu-Gly-l-Ala-OMe)

C 15 H 23 N 3 O 7 cristallise dans le systeme orthorhombique avec le groupe despace P2 1 2 1 2 1 . Affinement de la structure jusqua 0,045

N-(N-benzyloxycarbonyl-L-1,2,3,4-tetrahydroisoquinol-3-ylcarbonyl)-L-phenylalanine methyl ester, Z-L-Tic-L-Phe-OMe

The title compound, C 28 H 28 N 2 O 5 , is a terminally blocked dipeptide, conformationally constrained by the presence of a 1,2,3,4-tetrahydroisoquinoline residue (Tic). The conformation of the peptide linkage is trans [ω 1 =-177.0 (3) o ] and the main chain conformation is determined by the parameters φ 1 =-86.7 (4), ψ 1 =171.5 (3), φ 2 =-77.2 (4), ψ τ =160.1 (3) o . The side chain of Tic is in a g + conformation [χ 1 1 =56.0 (4) o ], whereas the phenylalanine side chain is in a g - conformation [χ 2 1 =- 68.8 (5) o ]

Subunit Assembly in Bovine Seminal Ribonuclease

The association of subunits in an oligomeric protein is a widespread phenomenon in the cellular organization, which promotes several advantages. A most important one is the regulation of catalytic activity through cooperative effects, mediated by specific interactions at subunit interface. Crystallographic studies of homologous proteins, which occur in different aggregation states, indicate that in most cases the globular monomer is stable on its own and is only marginally altered when it forms an oligomeric molecule. A notable exception is provided by some members of the ribonuclease family [1], which on aggregation show a substantial rearrangement of the tertiary structure of the monomer. The modification affects significantly the functionality of the active site, although the overall architecture of the site remains basically unchanged.