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Electron microscope study of mitochondrial 60S and cytoplasmic 80S ribosomes from Locusta migratoria
Abstract:
Purified mitochondrial ribosomes (60S) have been isolated from locust flight muscle. Purification could be achieved after lysis of mitochondria in 0.055 M MgCl(2). Mitochondrial 60S and cytoplasmic 80S ribosomes were investigated by electron microscopy in tissue sections, in sections of pellets of isolated ribosomes, and by negative staining of ribosomal suspensions. In negatively stained preparations, mitochondrial ribosomes show dimensions of approximately 270 x 210 x 215 A; cytoplasmic ribosomes measure approximately 295 x 245 x 255 A. From these values a volume ratio of mitochondrial to cytoplasmic ribosomes of 1: 1.5 was estimated. Despite their different sedimentation constants, mitochondrial ribosomes after negative staining show a morphology similar to that of cytoplasmic ribosomes. Both types of particles show bipartite profiles which are interpreted as "frontal views" and "lateral views." In contrast to measurements on negatively stained particles, the diameter of mitochondrial ribosomes in tissue sections is approximately 130 A, while the diameter of cytoplasmic ribosomes is approximately 180-200 A. These data suggest a volume ratio of mitochondrial to cytoplasmic ribosomes of 1:3. Subunits of mitochondrial ribosomes (40S and 25S) were obtained by incubation under dissociating conditions before fixation in glutaraldehyde. After negative staining, mitochondrial large (40S) subunits show rounded profiles with a shallow groove on a flattened side of the profile. Mitochondrial small subunits (25S) display elongated, triangular profiles.
Insights
Locust flight muscle mitochondrial ribosomes (60S) were purified and visualized using electron microscopy. Despite different sedimentation rates, their morphology is similar to cytoplasmic ribosomes (80S), with distinct subunit structures.
Area of Science:
- Cell Biology
- Molecular Biology
- Biochemistry
Background:
- Mitochondria possess their own ribosomes, distinct from cytoplasmic ribosomes, responsible for synthesizing essential mitochondrial proteins.
- Understanding the structural and morphological characteristics of mitochondrial ribosomes is crucial for comprehending mitochondrial function and biogenesis.
Purpose of the Study:
- To isolate and characterize purified mitochondrial ribosomes from locust flight muscle.
- To compare the morphology and dimensions of mitochondrial ribosomes with cytoplasmic ribosomes using electron microscopy.
Main Methods:
- Mitochondria were lysed in 0.055 M MgCl(2) to isolate 60S mitochondrial ribosomes.
- Electron microscopy (tissue sections, pellet sections, negative staining) was employed to visualize ribosomes and their subunits.
- Negative staining and glutaraldehyde fixation were used to examine ribosomal subunit morphology.
Main Results:
- Purified mitochondrial ribosomes (60S) were obtained from locust flight muscle.
- Electron microscopy revealed morphological similarities between mitochondrial (60S) and cytoplasmic (80S) ribosomes, despite differences in sedimentation constants.
- Volume estimations varied depending on the microscopy technique, suggesting different packing densities in situ versus in vitro.
- Mitochondrial ribosomal subunits (40S and 25S) exhibited distinct profiles, with the large subunit being rounded and the small subunit being elongated and triangular.
Conclusions:
- Locust flight muscle mitochondrial ribosomes share morphological similarities with cytoplasmic ribosomes.
- Distinct subunit structures (40S and 25S) were identified for mitochondrial ribosomes.
- The study provides insights into the structural organization of mitochondrial ribosomes, contributing to our understanding of mitochondrial protein synthesis.