Single crystals of amylose complexed with isopropanol or acetone were prepared by adding these precipitants to a metastable aqueous solution of amylose. With both precipitants, similar micrometre sized platelet crystals were obtained. They gave indistinguishable electron diffraction diagrams which could be indexed in an orthorhombic unit cell, with a = 28.26 A, b = 29.30 A, c = 8.01 A and in a space group P2(1)2(1)2(1) or P2(1)2(1)2. Within the unit cell, the amylose chains are organized in antiparallel pairs of parallel 6(5) amylose helices occupying 70% of the cell content, the remaining 30% consisting of isopropanol/acetone and water, with an estimate of 10 isopropanol/acetone molecules for 52 water molecules per unit cell. If the crystals are suspended in pure isopropanol at various temperatures or in pure methanol at room temperature, they undergo a de-solvation process that ultimately converts them into VH amylose. De-solvation with isopropanol left the crystals intact whereas with methanol, they became cracked during the shrinkage. An explanation is proposed for such difference.

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Conformational energy maps and descriptions of structures at the local minima are presented for the following fragments found in N-acetyllactosaminic type glycans of N-glycoproteins: GlcNAc beta(1-2)Man, GlcNAc beta(1-4)Man, GlcNAc beta(1-6)Man, Gal beta(1-4)GlcNAc, GlcNAc beta(1-3)Gal, Fuc alpha(1-6)GlcNAc, Fuc alpha(1-3)GlcNAc, Xyl beta(1-2)Man, Gal beta(1-3)GlcNAc and GlcNAc beta(1-6)Gal. These results are the second part of a data bank on glycoprotein moieties; five disaccharides found in oligomannose type N-glycans were analysed earlier (Imberty et al., 1990, Glycoconjugate J 7:27-54). In the present study, three to seven minima are found for each dimer. Conformations of disaccharide fragments found in the crystal structure of the complex of a biantennary octasaccharide with Lathyrus ochrus lectin are plotted on these energy maps. While the observed conformations are at predicted minima, they are not always at the minimum predicted to have the lowest energy. Further, not all observed conformations are stabilized by the exo-anomeric effect. We conclude that these oligosaccharides are highly flexible.

Lactobacillus helveticus can possess one or two cell envelope proteinases (CEPs), called PrtH2 and PrtH. The aim of this work was to explore the diversity of 15 strains of L. helveticus, isolated from various origins, in terms of their proteolytic activities and specificities on pure caseins or on milk casein micelles. CEP activity differed 14-fold when the strains were assayed on a synthetic substrate, but no significant differences were detected between strains possessing one or two CEPs. No correlation was observed between the proteolytic activities of the strains and their rates of acidification in milk. The kinetics of hydrolysis of purified ␣ s1 -and ␤-casein by L. helveticus whole cells was monitored using Tris-Tricine sodium dodecyl sulfate (SDS) electrophoresis, and for four strains, the peptides released were identified using mass spectrometry. While rapid hydrolysis of pure ␤-casein was observed for all strains, the hydrolysis kinetics of ␣ s1 -casein was the only criterion capable of distinguishing between the strains based on the number of CEPs. Fifty-four to 74 peptides were identified for each strain. When only PrtH2 was present, 22 to 30% of the peptides originated from ␣ s1 -casein. The percentage increased to 41 to 49% for strains in which both CEPs were expressed. The peptide size ranged from 6 to 33 amino acids, revealing a broad range of cleavage specificities, involving all classes of amino acids (Leu, Val, Ala, Ile, Glu, Gln, Lys, Arg, Met, and Pro). Regions resistant to proteolysis were identified in both caseins. When strains were grown in milk, a drastic reduction in the number of peptides was observed, reflecting changes in accessibility and/or peptide assimilation during growth.