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Site of carbamoylation of bovine gamma-II-crystallin by potassium [14C]cyanate.

ABSTRACT: One possible route to cataract formation may be via the carbamoylation of lens proteins due to increased concentrations of cyanate in the body resulting from uraemia associated with renal failure and with severe diarrhoea. Carbamoylation of gamma-II-crystallin, which is found in the lens core, could alter the surface charge network of the molecules, resulting in aggregation, increased light-scattering and hence cataract. We have attempted to locate the site(s) of carbamoylation in gamma-II-crystallin. gamma-II-Crystallin was isolated by gel chromatography and ion-exchange chromatography. gamma-II-Crystallin was then carbamoylated by incubation with potassium [14C]cyanate, followed by citraconylation and digestion with trypsin to give peptides that were separated by high-resolution ion-exchange chromatography. The amino acid compositions of the radioactive peptides were compared with the expected peptide composition for gamma-II-crystallin. The radioactive peptide compositions, which agreed with the theoretical peptides, all matched with the N-terminal region of gamma-II-crystallin and had in common the presence of the N-terminal glycine residue. It appears that the alpha-amino group of the N-terminal glycine was the main site of carbamoylation. This site forms part of the charge network on the surface of gamma-II-crystallin.

SUBMITTER: Martin S

PROVIDER: S-EPMC1133359 | biostudies-other | 1989 Sep

REPOSITORIES: biostudies-other

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Project description:The reactions of N-heterocyclic carbene CuI and AgI halides with potassium thio- or seleno-cyanate gave unexpected products. The attempted substitution reaction of bromido-(1,3-dibenzyl-4,5-di-phenyl-imidazol-2-yl-idene)silver (NHC*-Ag-Br) with KSCN yielded bis-[bis-(1,3-dibenzyl-4,5-di-phenyl-imidazol-2-yl-idene)silver(I)] tris-(thio-cyanato)-argentate(I) diethyl ether disolvate, [Ag(C29H24N2)2][Ag(NCS)3]·2C4H10O or [NHC*2Ag]2[Ag(SCN)3]·2Et2O, (1), while reaction with KSeCN led to bis-(μ-1,3-dibenzyl-4,5-diphenyl-2-seleno-imidazole-κ2 Se:Se)bis-[bromido-(1,3-dibenzyl-4,5-diphenyl-2-seleno-imid-azole-κSe)silver(I)] di-chloro-methane hexa-solvate, [Ag2Br2(C29H24N2Se)4]·6CH2Cl2 or (NHC*Se)4Ag2Br2·6CH2Cl2, (2), via oxidation of the NHC* fragment to 2-seleno-imidazole. This oxidation was observed again in the reaction of NHC*-Cu-Br with KSeCN, yielding catena-poly[[[(1,3-dibenzyl-4,5-diphenyl-2-seleno-imidazole-κSe)copper(I)]-μ-cyanido-κ2 C:N] aceto-nitrile monosolvate], {[Cu(CN)(C29H24N2Se)]·C2H3N} n or NHC*Se-CuCN·CH3CN, (3). Compound (1) represents an organic/inorganic salt with AgI in a linear coordination in each of the two cations and in a trigonal coordination in the anion, accompanied by diethyl ether solvent mol-ecules. The tri-blade boomerang-shaped complex anion [Ag(SCN)3]2- present in (1) is characterized by X-ray diffraction for the first time. Compound (2) comprises an isolated centrosymmetric mol-ecule with AgI in a distorted tetra-hedral BrSe3 coordination, together with di-chloro-methane solvent mol-ecules. Compound (3) exhibits a linear polymeric 1 ∞[Cu-C≡N-Cu-] chain structure with a seleno-imidazole moiety additionally coordinating to each CuI atom, and completed by aceto-nitrile solvent mol-ecules. Electron densities associated with an additional ether solvent mol-ecule in (1) and two additional di-chloro-methane solvent mol-ecules in (2) were removed with the SQUEEZE procedure [Spek (2015 ▸). Acta Cryst. C71, 9-18] in PLATON.

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Site of carbamoylation of bovine gamma-II-crystallin by potassium [14C]cyanate.

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