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The crystal structure of the antigen-binding fragment of a monoclonal antibody (8F5) that neutralizes human rhinovirus serotype 2 has been determined by X-ray diffraction studies. Antibody 8F5, obtained by immunization with native HRV2 virions, cross-reacts with peptides of the viral capsid protein VP2, which contribute to the neutralizing immunogenic site B in this serotype. The structure was solved by the molecular replacement method and has been refined to an R-factor of 18.9% at 2.8 A resolution. The elbow angle, relating the variable and constant modules of the molecule is 127 degrees, representing the smallest elbow angle observed so far in an Fab fragment. Furthermore, the charged residues of the epitope can be well accommodated in the antigen-binding site. This is the first crystal structure reported for an antibody directed against an icosahedral virus.

Porphobilinogen synthase was purified from ox liver by ammonium sulfate fractionation, heat denaturation and column chromatography (purification: 400-fold; specific activity 4.72 nkat). The molecular weight of the native enzyme obtained by thin-layer gel filtration is about 280 000. Using 8M urea in the presence of dithiothreitol as reducing agent, the molecule breaks down into 8 subunits of molecular weight 36 000 (dodecylsulfate gel electrophoresis); the preparation of aminoethylated subunit is described. According to the above-mentioned molecular weight and to the above-mentioned molecular weight and to the quantitative amino acid analysis after total hydrolysis, the following compositon of the enzymes subunit was calculated ASX23-25 Thr7 Ser23-24 Glx29-31 Pro22-23 Gly22-24 Ala36-37 Val23-26 Met7 Ile9 Leu34-35 Tyr10 Phe11-12 Lys11-12 Cys6-7 His6-8 Arg22 Trp1-2. The subunits, having two free sulfhydryl groups, therefore consists of a chain of about 306 amino acids. The Dansyl-Edman procedure did not enable identification of any free N-terminal amino acid. The acyl group blocking the N-terminus is an acetyl group. It was identified, after hydrazinolysis of the enzyme, by means of chromatographic comparison with 1-formyl-2-dansyl-hydrazine and 1-acetyl-2-dansylhydrazine, whose syntheses and UV spectra are described.

Ultrastructural stereological techniques were used to quantitate the phenotype of vascular smooth muscle cells grown in primary culture on a plastic substrate (control), on and within matrices of collagen type I, and on collagen type III, collagen type IV, or basement membrane Matrigel. The volume fraction of myofilaments (Vv myo) of freshly isolated cells at day 0 was 54.2 +/- 2.0%. By day 5 in culture, the Vv myo of cells grown on plastic, on collagen type I, and collagen type III had decreased significantly to 14.2 +/- 2.1%, 16.5 +/- 2.4%, and 16.3 +/- 2.9%, respectively. In contrast, smooth muscle cells grown within matrices of collagen type I, on collagen type IV, or on basement membrane Matrigel had a Vv myo of 30.7 +/- 1.5%, 30.8 +/- 4.2%, and 32.1 +/- 3.1%, respectively. These findings demonstrate that the presence of extracellular matrix components prevents modulation of smooth muscle phenotype early in culture and suggests that the extracellular matrix synthesized and secreted by smooth muscle in the normal vessel wall contributes to the maintenance of their contractile functional state.