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[RNA biosynthesis in mitochondria under conditions of prolonged inhibition of protein biosynthesis in rat liver cytoplasm].

When cytoplasmic protein synthesis is inhibited by cycloheximide (CHI) in vivo synthesis of water-soluble mitochondrial proteins and of mitochondrial RNA is decreased. These changes measured in isolated rat liver mitochondria are similar to those observed in vivo and correlate with the changes the synthesis of water-soluble proteins in mitochondria. When the cytoplasmic fraction (30,000 g-supernatant) had been added to the mitochondria showing decreased RNA synthesis, the RNA synthesis increased to the control level (the incubation conditions were favourable for the protein transport from microsomes to mitochondria). RNA synthesis in mitochondria was not stimulated by cytoplasmic fractions from the CHI-pretreated rats. After prolonged dialysis these fraction stimulated RNA synthesis even to a greater extent than cytoplasmic fractions from the untreated animals. Mitochondrial RNA polymerase activity (measured in mitochondrial extracts supplemented with exogenous DNA) was higher in extracts of mitochondria from livers of normal rats than in extracts of mitochondria from livers of animals injected with CHI.

Animals↗
PubMed1991

Extracellular matrix biosynthesis by cultured fetal rat lung epithelial cells. IV. Effects of chronic exposure to retinoic acid on growth, differentiation, and collagen biosynthesis.

Effects of chronic exposure to retinoic acid on a cell line (FRLE cells) established from the fetal rat lung type II alveolar epithelial cell have been studied. Chronic exposure to retinoic acid inhibited proliferation and altered the pattern of culture morphology at the light microscopic level. At the ultrastructural level, the development of lamellar body-like structures was inhibited. Although the rates of both total collagen and protein produced per cell were enhanced by chronic retinoic acid exposure, the increase in collagen production exceeded that of total protein synthesis. Chromatographic evaluation of collagen types I, III, IV, and V revealed increases in the amounts of radioactivity incorporated into each collagen type. However, the magnitudes of the increases differed for each collagen type, with the production of type IV collagen being the most enhanced. These analyses also indicated several additional effects on collagen production: 1) collagen type specific alterations in the ratio of secreted to cell associated molecules, 2) an increased ratio of type I homotrimers to type I heterotrimers, and 3) a decreased ratio of type V homotrimers to type V heterotrimers. These results indicate that chronic exposure to retinoic acid selectively affects collagen production in and differentiation of FRLE cells and establish that these changes are opposite to those observed under conditions of chronic exposure to EGF.

Animals↗
PubMed1993

Biosynthesis of monoterpenes: regio- and stereochemistry of (+)-3-carene biosynthesis.

Incubation of [1-3H1]geraniol with stem disks of Douglas fir (Pseudotsuga menziesii) and incubation of [1-3H1]geranyl pyrophosphate with both a soluble enzyme extract from Douglas fir and a partially purified preparation of (+)-3-carene synthase from lodgepole pine (Pinus contorta) resulted in the production of (+)-3-[3H] carene. Subsequent conversion of the product to car-3-en-5-one and to 4-isocaranone followed by base-catalyzed exchange of the alpha-hydrogens established that the 3H located at C1 in the geranyl substrate resided at C5 of (+)-3-carene. Incubation of the (+)-3-carene synthase preparation with (S)-[5-3H1, 4-14C]geranyl pyrophosphate resulted in the production of (+)-3-carene without loss of tritium, indicating that the 5-proR hydrogen is eliminated during cyclopropyl ring closure. Analysis of the conformational requirements for this 1,3 elimination involving the 5-proR hydrogen suggested that cyclopropyl ring formation occurs via a (4S)-alpha-terpinyl cation derived from the anti-endo cyclization of a (3S)-linalyl pyrophosphate intermediate. Kinetic analyses of the conversion of (1Z,3R)-[1-3H1]linalyl pyrophosphate, (1Z, 3S)-[1-3H1]linalyl pyrophosphate and [1-3H1]geranyl pyrophosphate by (+)-3-carene synthase revealed that the velocity of the reaction with the (3S)-linalyl enantiomer was 25-fold greater than the velocity with the (3R)-enantiomer and twice that of the natural substrate, geranyl pyrophosphate, thereby confirming this stereochemical prediction and also indicating that the cyclization of the linalyl intermediate is faster than the coupled isomerization and cyclization of the geranyl substrate. From these results, a model that details the regio- and stereochemistry of the enzymatic conversion of geranyl pyrophosphate to (+)-3-carene is proposed.

Bicyclic Monoterpenes↗