The biogenesis and function of eukaryotic porins

Summary Like most other mitochondrial proteins porin is synthesized in the cytosol and imported posttranslationally into the outer mitochondrial membrane. This transport follows the general rules for mitochondrial, protein import with a few aberrations: a) porin contains an,uncleaved NH₂-terminal signal sequence, b) also its carboxyterminus might be involved in the import process, and c) this transport does not seem to require a membrane potential , although it is ATP-dependent. Most likely the actual import step occurs at contact sites between the outer and the inner mitochondrial membrane and involved at least one receptor protein.Although porin is known to be the major gate through the outer mitochondrial membrane, its absence only causes transient respiratory problems in yeast cells. This could mean a) that there is a bypass for some mitochondrial functions in the cytosol and/or b) that there are alternative channel proteins in the outer membrane. The first idea is supported by the overexpression of cytosolic virus-like particles in yeast cells lacking porin and the second by the occurrence of residual pore activity in mitochondrial outer membrane purified from porinless mutant cells.     

Biogenesis of mitochondrial porin: the import pathway.

We review here the present knowledge about the pathway of import and assembly of porin into mitochondria and compare it to those of other mitochondrial proteins. Porin, like all outer mitochondrial membrane proteins studied so far is made as a precursor without a cleavable 'signal' sequence; thus targeting information must reside in the mature sequence. At least part of this information appears to be located at the amino-terminal end of the molecule. Transport into mitochondria can occur post-translationally. In a first step, the porin precursor is specifically recognized on the mitochondrial surface by a protease sensitive receptor. In a second step, porin precursor inserts partially into the outer membrane. This step is mediated by a component of the import machinery common to the import pathways of precursor proteins destined for other mitochondrial subcompartments. Finally, porin is assembled to produce the functional oligomeric form of an integral membrane protein which is characterized by its extreme protease resistance.     

The use mitochondrial mutants of yeast in the screening for new antimetabolites

Candida utilis Torulopsis globosa, , . T. globosa II-, 5% , .     

Proteolytic generation and aggregation of peptides from transmembrane regions: lung surfactant protein C and amyloid β-peptide

The formation of amyloid fibrils is associated with several devastating diseases in humans and animals, including e.g. Alzheimers disease (AD) and the spongiform encephalopathies. Here, we review and discuss the current knowledge on two amyloid peptides: lung surfactant protein C (SP-C) and the amyloid -peptide (A), implicated in human lung disease and in AD, respectively. Both these hydrophobic peptides are derived from the transmembrane region of their precursor protein, and can transit from a monomeric -helical state to a -sheet fibril. The helices of SP-C and A are composed of amino acid residues with inherently higher propensities for strand than helix conformation. Their helical states are stabilized by a membrane environment, and loss of membrane association thus promotes structural conversion and fibril formation. We speculate that the loss of structural context for sequences with a high propensity for formation of sheets may be a common feature of amyloid formation in general.Received 9 July 2003; received after revision 15 August 2003; accepted 3 September 2003     

Tumor necrosis factor-α inhibits collagen synthesis in human and rat granulation tissue fibroblasts

The purpose of the study was to examine the effects of tumor necrosis factor- (TNF-) on collagen gene expression in rat and human granulation tissue fibroblast cultures. The cells were exposed to 0.1, 1, 10, or 100 ng/ml of TNF-, and the rate of collagen synthesis was measured as synthesis of protein-bound³H-hydroxyproline. Total cellular RNA was isolated from fibroblasts, and measurements of specific cellular RNAs from fibroblasts were performed by Northern blot hybridizations using³²P-labeled cDNA probes. In cultures of rat granulation tissue fibroblasts TNF- decreased³H-hydroxyproline production to about 75% of that in controls and it also decreased pro1(I) and pro1(III) collagen mRNA levels, maximally to 33% and 23% of the control levels, respectively. In cultures of human granulation tissue fibroblasts a similar inhibiting effect in the production of collagen was seen. TNF- decreased the production of³H-hydroxyproline to 56% of the control value with a dose of 100 ng/ml also having an inhibiting effect on pro1(I) collagen mRNA levels of up to 43% of the control level. However, no effect was seen on pro1(III) collagen mRNA levels.     

Etude de l'hydrolyse et des propriétés toxiques vis-à-vis des mitochondries de maïs Texas,d'un insecticide,le méthomyl ou S-méthyl-N [(méthylcarbamoy)oxyl] thioacétimidate

Summary Methomyl, or S-methyl-N [(methylcarbamoyl)oxy] thioacetimidate, a common insecticide, has been found to be a specific poison of mitochondria of corn with Texas cytoplasm. Its hydrolysis under very mild acidic conditions affords thiomethyl methylthiosulphonate, which strongly inhibits the activity of CmST and N mitochondria of corn.     

Deamination by ‘Transformed’ mitochondrial amine oxidase of the ε-amino group of lysine and selective inhibition of this reaction by β-aminopropionitrile

« » - . -.     

Chromosomes and some issues of the evolution of the ground squirrel genusCitellus (Rodentia: Sciuridae)

Citellus (s. str.) relictus, C. dauricus C. pygmaeus (2=36, NF=72). . (Colobotis) erythrogenys . fulvus -. . (Urocitellus) undulatus (2n=32, NF=64) . columbianus. Citellus, , Citellus, . , .     

Responses of resistance and capacitance vessels at various frequency electrical stimulation of sympathetic nerves

Conclusion (1) The maximal reactions of cerebral resistance vessels arise at the stimulation frequency of 30 cps, the maximal reactions of capacitance vessels at the frequency of 10 cps. (2) Reactions of resistance vessels in the pulmonary lobe increase in the range of stimulation frequencies from 11–50 cps, maximal reactions of pulmonary capacitance vessels are observed at the frequency of 30–40 cps. (3) Reactions of resistance vessels situated below the abdominal aorta bifurcation increase progressively in the range of frequencies from 6–50 cps, the magnitude of capacitance vessel reaction reaching its maximum value at 20 cps.

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30 /, — 10 /. 50 /. 30–40 /, 20 /.

     

On the origin of the protein yolk in the oocytes ofAplysia depilans (Gastropoda,Opistobranchia)

Summary In the oocytes ofAplysia depilans it has been observed electronmicroscopically that gemmae or daughter-nucleoli separate from the nucleolus. These gemmae after having overcome the nuclear membrane, would aggregate together, even after transformation, into yolk globules. These observations seem to give plausibility to the hypothesis that there is a close relationship between production of ribonucleoproteic material by the nucleolus and yolk production.     

Unique occurrence of fenchol in the animal kingdom

Summary (–)--Fenchol, a compound occurring in plants but not heretofore reported to occur in an animal product, was isolated from volatiles released by adult male Mediterranean fruit flies,Ceratitis capitata Wiedemann, with the male's previously identified sex pheromones. It neither attracts females nor synergizes the pheromones, and its function remains unknown.The editors do not hold themselves responsible for the opinions expressed in the authors' brief reports. — Les auteurs sont seuls responsables des opinions exprimées dans ces brèves communications. — Für die Kurzmitteilungen ist ausschliesslich der Autor verantwortlich.—Per le brevi comunicazioni è responsabile solo l'autore. — . — Solo los autores son responsables de las opiniones expresadas en estas communicationes breves.Mention of a proprietary product in this paper does not constitute a recommendation or an endorsement of the product by the US Department of Agriculture.Acknowledgments. We thank C. Harding for assistance with extractions and fractionations, R.M. Waters for spectral analyses, M.S. Fujimoto and H. Higa for collecting the volatiles and conducting laboratory and cage bioassays, and T. Urago and S. Nakagawa for conducting the field tests.     

Uptake of D-glucose anomers by rat retina

Summary Uptake ofd-glucose anomers by isolated rat retina was studied. After 3 min incubation at 37°C in the presence of or anomer (750 g/ml), a significantly greater uptake (1.32 mg/g wet tissue) of -anomer was observed compared with that of -d-glucose (1.11 mg/g wet tissue). This result and other data suggest that the carrier ford-glucose transport in the retina prefers the -anomer stereospecifically.Acknowledgment. The authors are grateful to Mr S. Suzuki for his technical assistance.     

Recovery of isometric twitches after glycerol removal

1. , 110–220 , . 2. , . 3. .

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We thank Dr.G. A. Nasledov, Sechenov Institute of Evolutionary Physiology and Biochemistry, Leningrad, for kind permission to use his device for experiments with isolated muscle fibres.     

The biogenesis and function of eukaryotic porins.

Like most other mitochondrial proteins porin is synthesized in the cytosol and imported posttranslationally into the outer mitochondrial membrane. This transport follows the general rules for mitochondrial protein import with a few aberrations: a) porin contains an uncleaved NH2-terminal signal sequence, b) also its carboxyterminus might be involved in the import process, and c) this transport does not seem to require a membrane potential delta psi, although it is ATP-dependent. Most likely the actual import step occurs at contact sites between the outer and the inner mitochondrial membrane and involves at least one receptor protein. Although porin is known to be the major gate through the outer mitochondrial membrane, its absence only causes transient respiratory problems in yeast cells. This could mean a) that there is a bypass for some mitochondrial functions in the cytosol and/or b) that there are alternative channel proteins in the outer membrane. The first idea is supported by the overexpression of cytosolic virus-like particles in yeast cells lacking porin and the second by the occurrence of residual pore activity in mitochondrial outer membrane purified from porinless mutant cells.     

The molecular structure of the benzilic acid rearrangement product of 3α, 17β-diacetoxy-11-hydroxy-12-oxo-5β-androst-9(11)-ene

Zusammenfassung Die Struktur desp-Brombenzoates des Benzilsäureumlagerungsproduktes von 3, 17-Diacetoxy-11-hydroxy-12-oxo-5-9(11)-androsten wurde durch dreidimensionale Röntgenstrukturanalyse eines Einkristalls als 3-p-Brombenzoat des 11-Carboxy-3, 11, 17-trihydroxy-13-C-nor-5-androstan 11a, 17-Laktons erkannt.     

Zygotic mortality inEllobius lutescens (Rodentia: Microtinae)

і Ellobius, lutescens 50% , -- .     

Changes in the lumen of coronary vessels under oligemic hypotension

Conclusions The decrease of circulating blood volume, resulting in oligemic hypotension, may evoke in anaesthetized cat the active constrictory coronary vessel responses of 2 types, one occuring immediately after start of the hypotension and the other having a significantly prolonged latency.

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, , , , ( 4 ), ( 45 ).

     

X-ray research for polycrystals. The formation geometry of instrumental width of the diffractional line at the investigation of the polycrystals in the translucent X-rays

: , , , - , ().     

Structural changes accompanying the reversible cold inactivation of glyceraldehyde-3-phosphate dehydrogenase from rat skeletal muscle

qm -3- , 4° 0,15M NaCl, 5M , 4M - pH=7,6, ( 275–295 , –b _o , A ₁₉₃ , –A₂₂₅). , +20° 0.15M H₂PO₄.