PubMed Health⌕ Search

Biomedical subjects

A Gulik

Publications and source records attributed to A Gulik.

41 records · Page 3Linked to original sources
PubMed1976

Small-angle x-ray and light-scattering study of native and trypsin-modified methionyl-tRNA synthetase from Escherichia coli.

Small-angle X-ray scattering experiments were performed on an absolute scale on solutions of methionyl-tRNA synthetase from Escherichia coli in its native and trypsin-modified forms. A light-scattering study was performed on the same solutions to verify monodispersity. The structural parameters for the trypsin-modified enzyme, radius of gyration (2.48 nm), volume (90 nm3), surface/volume (1.5 nm-1) and the distribution of chords can account for an equivalent prolate ellipsoid of revolution having an axial ratio 2.3 and a maximum length of 9 nm, with a creviced surface. The rsults obtained for the native enzyme [i.e. radius of gyration (4.3 nm), volume (244 nm3), distribution of the scattering intensity and distribution of chords] exclude the possibility of a very compact quaternary structure and suggest that the enzyme consists of at least two globular parts, probably the two protomers, linked together by interactions involving a limited region of the structure.

Amino Acyl-tRNA Synthetases↗
PubMedDate not supplied

Crystallographic analysis of freeze-fractured three-dimensionally ordered specimens.

We describe here an original approach for solving the structure of three-dimensionally ordered specimens at low and medium resolutions. It combines freeze-fracture electron microscopy and quantitative image processing and has been first successfully applied to the crystallographic study of different lipid-containing cubic phases. The structure preservation during cryofixation is controlled by recording X-ray diffraction before and after freezing. Well frozen cubic phases show fracture planes which look like well defined cleavage planes of 3-D crystals. These fracture planes (domains) reveal a mosaic of 2D ordered sub-domains which are geometrically related to each other by simple crystallographic operations. The symmetry properties of the images mirror faithfully the symmetry of the space groups. The shifts and rotations observed between adjacent sub-domains are related to this symmetry. Different cubic phases display different fracture behavior, highly characteristic for a given space group. Interpretation of the averaged images of different domains in terms of molecular structure is done by the comparison of the averaged periodic motifs either with the corresponding sections of the electron density map (from X-ray diffraction data) or with the corresponding sections of a 3-D-space filling model. We show here that the same procedure may be applied to other three-dimensionally ordered specimens such as 3-D crystals of membrane proteins or of other proteins, including naturally occurring protein crystals of some secretory organelles. Finally, the same approach could also provide a powerful tool for the study of membrane protein crystallogenesis, particularly for the formation of 3-D crystals.

Animals↗
PubMedDate not supplied

Intralipid 10%: physicochemical characterization.

OBJECTIVES: Parenteral fat emulsions contain two populations of particles: artificial chylomicrons rich in triacylglycerols (TAG), and liposomes (bilayer of phospholipids [PL] enveloping an aqueous phase). Centrifugation permits isolating the liposomes in the infranatant called mesophase. The aim of the present work was to better characterize this mesophase chemically and to view the particles it contains by electron microscopy. METHODS: Electron microscopy (Philips 410) was performed after cryofracture on native 10% Intralipid, mesophase (centrifugation for 1 h at 27 000 g), and a liposome-enriched fraction (ring of density 1.010-1.030 g/l obtained after centrifuging mesophase in a KBr density gradient at 100 000 g for 24 h). The TAG and protein content of the mesophase was analyzed and the proteins partially characterized by immunodetection (Western-blot). RESULTS: This electron microscope study of 10% Intralipid gives evidence for the coexistence of artificial chylomicrons (mean diameter, 260 nm) and liposomes (43 nm), the latter being smaller than expected and containing 8% w/w TAG after purification. The solubilization of TAG in PL bilayers (reported to be < or = 3.1% w/w) might have been increased in parenteral emulsions by the manufacturing process or/and the high TAG/PL ratio. Minute amounts of proteins have also been detected and partially characterized using a specific antibody raised against the human 7 kDa Anionic Polypeptide Factor (APF), known to strongly interact with PL in bile. CONCLUSIONS: This work has shown that the size (mean diameter, 43 nm) of the liposomes present in 10% Intralipid is smaller than that usually assumed. Traces of hydrophobic proteins in the emulsion may account for certain allergic reactions sometimes observed in infused patients.

Blotting, Western↗