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Peptidyl-puromycin synthesis by free and membrane-bound ribosomes
Abstract:
The peptidyl transferase reaction, as measured by the formation of peptidyl-puromycin, was compared for free ribosomes and ribosomes bound to two types of membrane, the endoplasmic reticulum and the outer nuclear membrane. In most respects the reaction catalyzed by the three types of ribosome was similar, demonstrating that interaction of the 60 S ribosomal subunit with the membrane has little effect on the functioning of peptidyl transferase, a 60 S protein. However, both the rate and extent of synthesis of peptidyl puromycin were lower for ribosomes bound to the nuclear membrane than for free or microsome-bound ribosomes. This difference appears to be a direct consequence of the ribosome-membrane interaction, since ribosomes stripped from the nuclear membrane could not be distinguished from the other classes of ribosome.
Insights
Ribosome-membrane interactions, particularly with the nuclear membrane, minimally affect peptidyl transferase activity. However, nuclear membrane binding slightly reduces the rate and extent of peptidyl-puromycin synthesis by ribosomes.
Area of Science:
- Molecular Biology
- Cell Biology
- Biochemistry
Background:
- Ribosomes are crucial for protein synthesis, catalyzing the peptidyl transferase reaction.
- Ribosomes can exist freely in the cytoplasm or be bound to cellular membranes like the endoplasmic reticulum and outer nuclear membrane.
- The functional impact of ribosome-membrane interactions on peptidyl transferase activity remains an area of investigation.
Purpose of the Study:
- To compare the peptidyl transferase activity of free ribosomes versus ribosomes bound to the endoplasmic reticulum and outer nuclear membrane.
- To determine if membrane binding affects the peptidyl transferase enzyme, a component of the 60S ribosomal subunit.
Main Methods:
- Assessed peptidyl transferase activity by measuring the formation of peptidyl-puromycin.
- Compared this reaction for free ribosomes, endoplasmic reticulum-bound ribosomes, and outer nuclear membrane-bound ribosomes.
- Investigated the effect of membrane stripping on ribosome function.
Main Results:
- Peptidyl transferase activity was largely similar across free, endoplasmic reticulum-bound, and outer nuclear membrane-bound ribosomes.
- Ribosomes bound to the outer nuclear membrane exhibited a lower rate and extent of peptidyl-puromycin synthesis compared to free or microsome-bound ribosomes.
- Ribosomes detached from the nuclear membrane showed no functional difference from other ribosome populations, indicating the effect is due to membrane interaction.
Conclusions:
- Membrane interaction, specifically with the outer nuclear membrane, has a modest inhibitory effect on the rate and extent of peptidyl transferase activity.
- The peptidyl transferase enzyme itself (a 60S ribosomal protein) is not fundamentally altered by membrane binding.
- The observed differences in activity are a direct consequence of the ribosome-membrane association rather than intrinsic changes in the ribosome.