Protein-mediated fusion of liposomes with microsomal membranes of Aspergillus niger: evidence for a complex mechanism dealing with membranous and cytosolic fusogenic proteins.

Membrane fusion is a fundamental and wide-spread phenomenon in the functioning of cells. Many studies were carried out concerning fusion of plasma membranes as for example cell-cell fusions or uptake by cells of lipid-enveloped viruses. The present study deals with the interaction of intracellular membranes of Aspergillus niger with artificial membranes (liposomes).

Vitamin K1 binding protein in milk.

Cow's milk has been shown to contain a protein complex which is able to bind vitamin K1 in a reversible manner. This binding property has been investigated by the celite method which consists in creating a dynamic equilibrium between the adsorbent, the celite and the protein complex for the ligand (vitamin K1). Based on competition experiment, the binding is specific and the vitamin K1 binding protein complex has a molecular weight equal to or higher than 7.

The phosphatidyl choline exchange properties in the cytosol of Aspergillus niger.

The presence of a PC-binding activity in the cytosol of Aspergillus niger van Tieghem has been established by measuring the reversible exchange of labeled DPC between an adsorbent (celite) and the cytosol. We have shown that this exchange is dependent upon the temperature and the ionic strength and it varies linearly with the protein concentration. This PC-binding activity is able to discriminate between DPC and some other phospholipids.

Spatial aspects of mannosyl phosphoryl retinol formation.

Rat liver microsomes catalyze the transfer of mannose from GDPmannose to both retinyl phosphate and dolichyl phosphate to form mannosylphosphorylretinol, mannosylphosphoryldolichol and GDP. The two reactions differ in term of reversibility. In fact, a 200-fold isotopic dilution of GDP[14C]mannose by unlabeled GDPmannose causes mannosylphosphoryldolichol labeling to disappear almost completely, while mannosylphosphorylretinol labeling remains at the same level.