Effect of ribosome stripping procedures on antigenicity and conformation of endoplasmic reticulum membrane

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.

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

1. The activity of the enzyme protein disulphide-isomerase (EC 5.3.4.1) was used to measure the binding of ribosomal fractions to reticular membranes from the liver of unstarved male rats. 2. Membranes degranulated by treatment with KCl plus puromycin and washed by centrifugation through 0.5 M-KCl bound oligoribosomes but not monoribosomes. 3. Substitution of 0.25 M-KCl for 0.5 M-KCl in the wash solution produced membranes that bound monoribosomes and 60 S subunits in addition to oligoribosomes. 4. The binding of all classes of ribosomes to smooth and 'lightly granulated' rough membranes was activated by oestradiol. The hormone activation was much greater with polyribosomes from fed rats than for monoribosomes or oligoribosomes from starved rats. 5. Exposure of rough membranes to centrifugal forces caused them to undergo partial degranulation, as demonstrated by unmasking of protein disulphide-isomerase activity.