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At least 1,297 records · Page 72Linked to original sources
PubMed1978

Chloroplast membrane biogenesis in Chlamydomonas: correlation between the formation of membrane components and membrane structure.

The y-1 mutant of Chlamydomonas reinhardi, when allowed to green in the presence of chloramphenicol (CAP), an inhibitor of protein synthesis on 70s ribosomes, form photosynthetic membranes which contain somewhat less chlorophyll than those of cells greened in the absence of the drug. Photosystem I and II activities are drastically reduced in the CAP-greened cells, and specific alterations in the polypeptide composition of the thylakoid membranes are also observed. We have examined the internal structure of the thylakoid membranes from cells greened in the presence and absence of CAP, and have found that the large particles observed on the exoplasmic fracture face (EF) are substantially reduced in size and number in the CAP-greened cells. This structural defect seems related to the absence of significant photo-system activities in the CAP-greened cells, despite the presence of most major membrane polypeptides. We suggest that CAP treatment results in a failure of the cell to organize functional reaction complexes, and is structurally reflected in the absence of large (EF) particles in such membranes. This defect can be repaired by allowing the affected cells to re-green in the absence of the drug, and the large particles reappear, paralleling an increase in photosynthetic activity.

Chlamydomonas↗
PubMed2005

The RIO kinases: an atypical protein kinase family required for ribosome biogenesis and cell cycle progression.

Atypical protein kinases (aPKs) include proteins known to be involved in the phosphorylation-mediated regulation of a wide variety of cellular processes, as well as some for which the function is, as yet, unknown. At present, 13 families of aPKs have been identified in the human genome. This review briefly summarizes their known properties, but concentrates in particular on the RIO family of aPKs. Representatives of this family are present in organisms varying from archaea to humans. All these organisms contain at least two RIO proteins, Rio1 and Rio2, but a third Rio3 group is present in multicellular eukaryotes. Crystal structures of A. fulgidus Rio1 and Rio2 have shown that whereas the overall fold of these enzymes resembles typical protein kinases, some of the kinase structural domains, particularly those involved in peptide substrate binding, are not present. The mode of binding of nucleotides also differs from other kinases. While the enzymatic activity of Rio1 and Rio2 has been demonstrated and both have been shown to be essential in S. cerevisiae and required for proper cell cycle progression and chromosome maintenance, the biological substrates of RIO proteins still remain to be identified.

Amino Acid Sequence↗
PubMed2004

Mitochondrial biogenesis as a cellular signaling framework.

The identification, more than 50 years ago, of mitochondria as the site of oxidative energy metabolism has prompted studies that have unraveled the complexity of the numerous biosynthetic and degradative reactions, fundamental to cell function, carried out by these organelles. These activities depend on a distinctive mitochondrial structure, with different enzymes and reactions localized in discrete membranes and aqueous compartments. The characteristic mitochondrial structural organization is the product of both synthesis of macromolecules within the mitochondria and the import of proteins and lipids synthesized outside the organelle. Synthesis and import of mitochondrial components are required for mitochondrial proliferation, but rather than producing new organelles, these processes may facilitate the growth of pre-existing mitochondria. Recent evidence indicates that these events are regulated in a complex way by several agonists and environmental conditions, through activation of specific transcription factors and signaling pathways. Some of these are now being elucidated. Generation of nitric oxide (NO) appears to be a novel player in this scenario, possibly acting as a unifying molecular switch to trigger the whole mitochondriogenic process.

Adipose Tissue, Brown↗
PubMed2006

Roles of LAMP-1 and LAMP-2 in lysosome biogenesis and autophagy.

The lysosomal membrane proteins LAMP-1 and LAMP-2 are estimated to contribute to about 50% of all proteins of the lysosome membrane. Surprisingly, mice deficient in either LAMP-1 or LAMP-2 are viable and fertile. However, mice deficient in both LAMP-1 and LAMP-2 have an embryonic lethal phenotype. These results show that these two major lysosomal membrane proteins share common functions in vivo. However, LAMP-2 seems to have more specific functions since LAMP-2 single deficiency has more severe consequences than LAMP-1 single deficiency. Mutations in LAMP-2 gene cause a lysosomal glycogen storage disease, Danon disease, in humans. LAMP-2 deficient mice replicate the symptoms found in Danon patients including accumulation of autophagic vacuoles in heart and skeletal muscle. In embryonic fibroblasts, mutual disruption of both LAMPs is associated with an increased accumulation of autophagic vacuoles and unesterified cholesterol, while protein degradation rates are not affected. These results clearly show that the LAMP proteins fulfil functions far beyond the initially suggested roles in maintaining the structural integrity of the lysosomal compartment.

Animals↗
PubMed1973

Biogenesis of mitochondria. The effects of physiological and genetic manipulation of Saccharomyces cerevisiae on the mitochondrial transport systems for tricarboxylate-cycle anions.

1. Kinetic and equilibrium parameters for the uptake of l-malate, succinate, citrate and alpha-oxoglutarate by fully functional mitochondria of Saccharomyces cerevisiae were determined. 2. The uptake of l-malate and succinate is mediated by a common carrier, and two other distinct carriers mediate the uptake of citrate and alpha-oxoglutarate. 3. The properties of the carrier systems for l-malate, succinate and citrate closely resemble those of mammalian mitochondria, but the alpha-oxoglutarate carrier differs from the mammalian system in minor respects. 4. The composition of the yeast mitochondria was extensively manipulated by (a) anaerobiosis, (b) catabolite repression, (c) inhibition of mitochondrial protein synthesis and (d) elimination of mitochondrial DNA by mutation. 5. The carrier systems for l-malate, succinate, citrate and alpha-oxoglutarate are essentially similar in the five different types of mitochondria. 6. It is concluded that all the protein components of the carrier systems for l-malate, succinate, citrate and alpha-oxoglutarate are coded by nuclear genes and synthesized extramitochondrially by cell-sap ribosomes.

Anaerobiosis↗
PubMed1973

Biogenesis of mitochondria. A requirement for mitochondrial protein synthesis for the formation of a normal adenine nucleotide transporter in yeast mitochondria.

1. Parameters of ATP uptake by fully functional Saccharomyces cerevisiae mitochondria, including kinetic constants, binding constants and sensitivity to atractylate, closely resemble those of mammalian mitochondria. Scatchard plots of atractylate-sensitive adenine nucleotide binding indicate two distinct sites of high affinity (binding constant, K(D)'=1mum), and low affinity (binding constant, K(D)''=20mum) in the ratio 1:3. Uptake has high Arrhenius activation energies (+35 and +57kJ/mol), above and below a transition temperature of 11 degrees C. Atractylate-insensitive ATP uptake is apparently not saturable and has a low Arrhenius activation energy (6kJ/mol), suggesting a non-specific binding process. 2. Kinetic and binding constants for ATP uptake are not significantly changed in catabolite-repressed or anaerobic mitochondrial structures. 3. Inhibition of the mitochondrial protein-synthesizing system by growth of cells in the presence of erythromycin, or loss of mitochondrial DNA by mutation profoundly alters the adenine nucleotide transporter. ATP uptake becomes completely insensitive to atractylate, and the high-affinity binding site is lost. However, the adenine nucleotide transporter does not appear to be totally eliminated, as a moderate amount of saturable low-affinity ATP binding remains. 4. It is concluded that products of the mitochondrial protein-synthesizing system, probably coded by mitochondrial DNA, are required for the normal function of the adenine nucleotide transporter.

Adenine Nucleotides↗
PubMed1973

Biogenesis of mitochondria. The effects of altered membrane lipid composition on cation transport by mitochondria of Saccharomyces cerevisiae.

1. The fatty acid composition of the membrane lipids of a fatty acid desaturase mutant of Saccharomyces cerevisiae was manipulated by growing the organism in a medium containing defined fatty acid supplements. 2. Mitochondria were obtained whose fatty acids contain between 20% and 80% unsaturated fatty acids. 3. Mitochondria with high proportions of unsaturated fatty acids in their lipids have coupled oxidative phosphorylation with normal P/O ratios, accumulate K(+) ions in the presence of valinomycin and an energy source, and eject protons in an energy-dependent fashion. 4. If the unsaturated fatty acid content of the mitochondrial fatty acids is lowered to 20%, the mitochondria simultaneously lose active cation transport and the ability to couple phosphorylation to respiration. 5. The loss of energy-linked reactions is accompanied by an increased passive permeability of the mitochondria to protons. 6. Free fatty acids uncouple oxidative phosphorylation in yeast mitochondria and the effect is reversed by bovine serum albumin. 7. The free fatty acid contents of yeast mitochondria are unaffected by depletion of unsaturated fatty acids, and free fatty acids are not responsible for the uncoupling of oxidative phosphorylation in organelles depleted in unsaturated fatty acids. 8. It is suggested that the loss of energy-linked reactions in yeast mitochondria that are depleted in unsaturated fatty acids is a consequence of the increased passive permeability to protons, and is caused by a change in the physical properties of the lipid phase of the inner mitochondrial membrane.

Biological Transport↗