Biomedical subjects

J A Hanover

Publications and source records attributed to J A Hanover.

75 records · Page 5Linked to original sources

PubMed1980

N-Linked glycoprotein assembly. Evidence that oligosaccharide attachment occurs within the lumen of the endoplasmic reticulum.

The transbilayer orientation of the oligosaccharide chain transferred from oligosaccharide-lipid to endogenous protein acceptors in sealed hen oviduct microsomes has been examined using endo-beta-N-acetylglucosaminidase H as a topological probe. The oligosaccharide moiety of these acceptors was released by the enzyme only under conditions where the microsomes were made permeable to macromolecules. The release of the oligosaccharide chain by endo-beta-N-acetylglucosaminidase H was not increased by removal of ribosomes or by mild trypsinization of the sealed microsomes. The endogenous acceptors were shown to be membrane-associated proteins that are not a part of the mRNA . ribosome . tRNA . nascent chain complex. From these results we conclude that the transfer of oligosaccharide from oligosaccharide-lipid occurs at the luminal face of the rough endoplasmic reticulum.

Acetylglucosaminidase↗

PubMed1979

The topological orientation of N,N'-diacetylchitobiosylpyrophosphoryldolichol in artificial and natural membranes.

Purified N,N'-diacetylchitobiosylpyrophosphoryldolichol (chitobiosyl-lipid) in the presence of detergent was shown to act as a substrate for the soluble enzyme galactosyltransferase. The nature of this transfer reaction and the galactose-containing trisaccharide-lipid product have been partially characterized. Using galactosyltransferase as a probe, the topolical arrangement of chitobiosyl-lipid in both artificial and natural membranes has been examined. When incorporated into unilamellar liposomes made from phosphatidylcholine, the disaccharide residue of chitogiosyl-lipid adopts a random transbilayer orientation. Furthermore, no significant mobility in the transverse plane of the membrane (i.e. flip-flop) is detectable. Using both sealed total microsomes or isolated rough microsomes from hen oviduct, the topology of chitobiosyl-lipid after its biosynthesis in the membrane has been determined. The results suggest that, once formed, chitobiosyl-lipid is a relatively static component of the membrane and is oriented with its disaccharide residue facing the lumen of the endoplasmic reticulum.

Acetylglucosamine↗

PubMedDate not supplied

Nuclear pore complex ion channels (review).

It is currently thought that nuclear pore complexes (NPCs) primarily govern nucleocytoplasmic interactions via selective recognition and active transport of macromolecules. However, in various nuclear preparations, patch-clamp and fluorescence, luminiscence and ion microscopy support classical microelectrode measurements indicating that monoatomic ion flow across the nuclear envelope (NE) is strictly regulated. Gating of large conductance nuclear envelope ion channels (NICs) somewhat resembles that of gap junctional channels. In other respects, NICs are distinct in that they require cytosolic factors, are blocked by wheat germ agglutinin and are blocked and/or modified by antibodies to epitopes of NPC glycoproteins. Therefore, NIC activity, recorded as electrical current/conductance is likely to be intrinsic to NPCs. This observation suggests a potential use for the patch-clamp technique in establishing the mechanisms underlying nuclear pore gating in response to cytosolic and nucleosolic factors such as transcription and growth factors, oncogene and proto-oncogene products and receptors for retinoids, steroids and thyroid hormone. NIC activity may also be useful in evaluating the mechanisms of nuclear import of foreign nucleic acid material such as that contained in virons and viroids. Finally, in consideration to the electrophysiological data accumulated so far, the study of nuclear pore ion channel activity may help our understanding of other important issues such as cell suicide, programmed cell death or apoptosis.

Animals↗