Organellar clusters formed by mitochondrial-rough endoplasmic reticulum associations: an ordered arrangement of mitochondria in hepatocytes. 1995

J Cascarano, and P A Chambers, and E Schwartz, and P Poorkaj, and R E Gondo
Department of Biology, University of California at Los Angeles 90024-1606, USA.

Our objective was to determine if mitochondrial-rough endoplasmic reticulum (mt-RER) associations provide for an ordered arrangement of mitochondria in the cell. If such an ordered arrangement exists, it might be manifested by grouping of mitochondria according to size and biochemical properties. Liver homogenate was subjected to rate zonal centrifugation for fractionating mitochondrial clusters. These clusters were then examined for morphological and biochemical characteristics. Scanning electron microscopy (SEM) showed that (1) mitochondria were held together in clusters by rough endoplasmic reticulum, (2) clusters consisted of mitochondria of comparable size, and (3) a 45-fold difference in average mitochondrial volume existed between the organelles of the fastest and slowest sedimenting clusters. Transmission electron microscopy (TEM) affirmed that all of the organellar clusters examined were mitochondria associated with rough endoplasmic reticulum. Cytochrome oxidase and mitochondrial DNA were found to be proportional to mitochondrial volume, indicating that these components were synthesized in proportion to increases in volume. Conversely, succinic dehydrogenase and ornithine carbamoyl transferase were increased disproportionately (2.9-fold and six-fold, respectively) with increase in mitochondrial volume. It is evident from this biochemical heterogeneity that clusters composed of larger mitochondria differ functionally from clusters of smaller mitochondria. The size-ordered arrangement suggests that this organization is in some way related to the biogenesis of hepatocyte mitochondria. It is also conjectured that the biochemical heterogeneity is a consequence of addition of selected proteins (e.g., succinic dehydrogenase and carbamoyl transferase) to mitochondria in a developmental process as they mature into larger organelles.

UI MeSH Term Description Entries
D008099 Liver A large lobed glandular organ in the abdomen of vertebrates that is responsible for detoxification, metabolism, synthesis and storage of various substances. Livers
D008297 Male Males
D008854 Microscopy, Electron Microscopy using an electron beam, instead of light, to visualize the sample, thereby allowing much greater magnification. The interactions of ELECTRONS with specimens are used to provide information about the fine structure of that specimen. In TRANSMISSION ELECTRON MICROSCOPY the reactions of the electrons that are transmitted through the specimen are imaged. In SCANNING ELECTRON MICROSCOPY an electron beam falls at a non-normal angle on the specimen and the image is derived from the reactions occurring above the plane of the specimen. Electron Microscopy
D008855 Microscopy, Electron, Scanning Microscopy in which the object is examined directly by an electron beam scanning the specimen point-by-point. The image is constructed by detecting the products of specimen interactions that are projected above the plane of the sample, such as backscattered electrons. Although SCANNING TRANSMISSION ELECTRON MICROSCOPY also scans the specimen point by point with the electron beam, the image is constructed by detecting the electrons, or their interaction products that are transmitted through the sample plane, so that is a form of TRANSMISSION ELECTRON MICROSCOPY. Scanning Electron Microscopy,Electron Scanning Microscopy,Electron Microscopies, Scanning,Electron Microscopy, Scanning,Electron Scanning Microscopies,Microscopies, Electron Scanning,Microscopies, Scanning Electron,Microscopy, Electron Scanning,Microscopy, Scanning Electron,Scanning Electron Microscopies,Scanning Microscopies, Electron,Scanning Microscopy, Electron
D008930 Mitochondria, Liver Mitochondria in hepatocytes. As in all mitochondria, there are an outer membrane and an inner membrane, together creating two separate mitochondrial compartments: the internal matrix space and a much narrower intermembrane space. In the liver mitochondrion, an estimated 67% of the total mitochondrial proteins is located in the matrix. (From Alberts et al., Molecular Biology of the Cell, 2d ed, p343-4) Liver Mitochondria,Liver Mitochondrion,Mitochondrion, Liver
D009954 Ornithine Carbamoyltransferase A urea cycle enzyme that catalyzes the formation of orthophosphate and L-citrulline (CITRULLINE) from CARBAMOYL PHOSPHATE and L-ornithine (ORNITHINE). Deficiency of this enzyme may be transmitted as an X-linked trait. EC 2.1.3.3. Ornithine Transcarbamylase,Ornithine Carbamylphosphate Transferase,Carbamoyltransferase, Ornithine,Carbamylphosphate Transferase, Ornithine,Transcarbamylase, Ornithine,Transferase, Ornithine Carbamylphosphate
D003576 Electron Transport Complex IV A multisubunit enzyme complex containing CYTOCHROME A GROUP; CYTOCHROME A3; two copper atoms; and 13 different protein subunits. It is the terminal oxidase complex of the RESPIRATORY CHAIN and collects electrons that are transferred from the reduced CYTOCHROME C GROUP and donates them to molecular OXYGEN, which is then reduced to water. The redox reaction is simultaneously coupled to the transport of PROTONS across the inner mitochondrial membrane. Cytochrome Oxidase,Cytochrome aa3,Cytochrome-c Oxidase,Cytochrome Oxidase Subunit III,Cytochrome a,a3,Cytochrome c Oxidase Subunit VIa,Cytochrome-c Oxidase (Complex IV),Cytochrome-c Oxidase Subunit III,Cytochrome-c Oxidase Subunit IV,Ferrocytochrome c Oxygen Oxidoreductase,Heme aa3 Cytochrome Oxidase,Pre-CTOX p25,Signal Peptide p25-Subunit IV Cytochrome Oxidase,Subunit III, Cytochrome Oxidase,p25 Presequence Peptide-Cytochrome Oxidase,Cytochrome c Oxidase,Cytochrome c Oxidase Subunit III,Cytochrome c Oxidase Subunit IV,Oxidase, Cytochrome,Oxidase, Cytochrome-c,Signal Peptide p25 Subunit IV Cytochrome Oxidase,p25 Presequence Peptide Cytochrome Oxidase
D004272 DNA, Mitochondrial Double-stranded DNA of MITOCHONDRIA. In eukaryotes, the mitochondrial GENOME is circular and codes for ribosomal RNAs, transfer RNAs, and about 10 proteins. Mitochondrial DNA,mtDNA
D004721 Endoplasmic Reticulum A system of cisternae in the CYTOPLASM of many cells. In places the endoplasmic reticulum is continuous with the plasma membrane (CELL MEMBRANE) or outer membrane of the nuclear envelope. If the outer surfaces of the endoplasmic reticulum membranes are coated with ribosomes, the endoplasmic reticulum is said to be rough-surfaced (ENDOPLASMIC RETICULUM, ROUGH); otherwise it is said to be smooth-surfaced (ENDOPLASMIC RETICULUM, SMOOTH). (King & Stansfield, A Dictionary of Genetics, 4th ed) Ergastoplasm,Reticulum, Endoplasmic
D000818 Animals Unicellular or multicellular, heterotrophic organisms, that have sensation and the power of voluntary movement. Under the older five kingdom paradigm, Animalia was one of the kingdoms. Under the modern three domain model, Animalia represents one of the many groups in the domain EUKARYOTA. Animal,Metazoa,Animalia

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