The binding of monoribosomes, oligoribosomes and polyribosomes to reticular membranes from rat liver

Ribosomes mask cytochrome b5 on rough microsomal vesicles

Cytochrome b5 is unmasked on the removal of ribosomes by chemical degranulation of rat liver microsomes. Reattachment of ribosomes to stripped membranes remasks this enzyme on the membrane surface. This haemoprotein may be involved either in the attachment of ribosomes to reticular membranes or in protein biosynthesis by membrane-bound ribosomes.

4-Dimethylaminoazobenzene interferes with the binding of ribosomes to reticular membranes

Treatment of chemically degranulated rough endoplasmic reticulum (RER) with 4-dimethylamino-azobenzene (4-DAB) partly damages binding of fresh polyribosomes to both the lighter and heavier fractions of reconstituted RER. Also, treatment of ribosomes with 4-DAB seemed to inhibit their binding to the chemically stripped RER (DRER) appearing both as lighter and heavier rough membrane layers after reconstitution. The interaction of 4-DAB with stripped microsomal fraction and ribosomes might be introducing certain conformational constraints into their proteins, thus crippling the binding of the ribosomes to reticular membranes.

A comparison of accessibility of ribosomal proteins on free and membrane-bound ribosomes: the ribosomal proteins potentially involved in ribosome-membrane binding

The relative accessibility of rat liver ribosomal proteins to reductive methylation was examined using membrane-bound and free ribosomes. Comparisons indicated that 12-13 large ribosomal proteins are masked by ribosomal association with membranes. These consisted of L8, L10, L17, L26-28, L31 and L36, and probably also include L4, L5, L7 and L29. These proteins seem to surround a region centered about L3 and may partly define a ribosomal channel through which the nascent peptide emerges. Approx. 10-20% of the large ribosomal subunit surface area is shielded by the membrane.