An electrophoretically purified allophycocyanin-linker complex, AP⅐L C 7.8 , from phycobilisomes of Mastigocladus laminosus has been crystallized in the orthorhombic space group P2 1 2 1 2 1 . Cryocrystallographic x-ray measurements enabled the structural analysis of the complex at a resolution of 2.2 Å. The asymmetric unit contains two sideto-side associated ''trimeric'' (␣␤) 3 allophycocyanin complexes comprising the linker polypeptide in a defined orientation inside the trimer. The linker representing a protein fold related to the prosegment of procarboxypeptidase A is in contact with only two of the three ␤-subunits and directly interacts with the corresponding chromophores of these proteins. In addition to a modulation of the chromophores' spectral properties, the linker polypeptide attracts the ␣␤-subcomplexes, thereby bringing the ␤-chromophores closer together. These results will enable interpretations of energytransfer mechanisms within phycobiliproteins.

In the structure of the GST-glutathione complex, two conserved water molecules are observed, one of which hydrogen bonds directly to the sulphur atom of glutathione and the other forms hydrogen bonds with residues around the glutathione-binding site. These water molecules are absent from the structure of the Meisenheimer complex bound to GST, implicating that deprotonation of the cysteine occurs during formation of the ternary complex which involves expulsion of the inner bound water molecule. The comparison of our structures with known mu class GST structures show differences in the location of the electrophile-binding site (H-site), explaining the different substrate specificities of the two classes. Fluorescence measurements are in agreement with the position of the N-morpholino-ethansulfonic acid, close to Trp28, identifying a possible ligandin-substrate binding site.

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Indolmycin specifically prevents the formation of tryptophanyl-tRNA in a prokaryotic system in vifvo using Eschevichia coli enzymes. However, the drug has little effect in an eukaryotic system in v i m (rat liver enzymes). Analysis of the type of inhibition revealed that indolmycin competes with tryptophan as a pure competitive inhibitor of prokaryotic tryptophanyl-tRNA ligase.Most of the antibiotics inhibiting protein synthesis interfere directly with prokaryotic ribosomal functions. A small number of antibiotics act as inhibitors of steps taking place prior to translation (for review see [l]). For example, the drug borrelidin prevents the formation of threonyl-tRNA in some bacterial speciesIn this paper we show that indolmycin specifically inhibits the tryptophanyl-tRNA ligase from Escherichia coli whereas the corresponding ligase from rat liver is affected much less.PI. MATERIALS AND METHODS Muter ialsATP and tRNA from E. coli and calf liver were obtained from Boehringer, Mannheim ; the radioactive amino acids were obtained from New England Nuclear; Instagel scintillation liquid from Packard ; the filters from Sartorius ; the total synthesis of indolmycin followed described procedures [3 -61; all other chemicals were from Merck, Darmstadt. The 300000xg supernatant from rat liver was a generous gift from Dr F. Grummt

The polyunsaturated fatty acid composition of colostrum in a high risk newborn population shows associations with atopic sensitization at the age of 1 year and may be predictive for later atopic disease.