Effects of glucose, tetrapyrroles and protein kinase C activators on cell proliferation in cultures of Saccharomyces cerevisiae

Abstract Saccharomyces cerevisiae was inoculated into a yeast nitrogen base with either glycerol or glucose as carbon source. Cell proliferation was followed by colony counts on agar medium. Cells in the glycerol-supplemented medium divided less than once in 10 days. When glucose, 6-deoxy-glucose or protoporphyrin IX was added, the cells had doubling times of about 24 h and increased in number to about 0.5 × 10⁶ cells ml⁻¹ Addition of either of the protein kinase C activators oleoyl-acetylglycerol or phorbol-12-myristate-13-acetate did not activate cell proliferation in the glycerol medium. However, when (i) glucose was combined with either protoporphyrin IX or chlorophyllin, or (ii) either protoporphyrin IX or chlorophyllin was combined with either of the protein kinase C activators, the cells had doubling times of about 12 h. Hence, (i) glucose can act as both a carbon source and a signalling molecule for proliferation, and (ii) two systems are involved in activating cell proliferation in S. cerevisiae : one operating through a protein kinase C system and another through a guanylate cyclase system.     

Cardiolipin biosynthesis and remodeling enzymes are altered during development of heart failure

Cardiolipin (CL) is responsible for modulation of activities of various enzymes involved in oxidative phosphorylation. Although energy production decreases in heart failure (HF), regulation of cardiolipin during HF development is unknown. Enzymes involved in cardiac cardiolipin synthesis and remodeling were studied in spontaneously hypertensive HF (SHHF) rats, explanted hearts from human HF patients, and nonfailing Sprague Dawley (SD) rats. The biosynthetic enzymes cytidinediphosphatediacylglycerol synthetase (CDS), phosphatidylglycerolphosphate synthase (PGPS) and cardiolipin synthase (CLS) were investigated. Mitochondrial CDS activity and CDS-1 mRNA increased in HF whereas CDS-2 mRNA in SHHF and humans, not in SD rats, decreased. PGPS activity, but not mRNA, increased in SHHF. CLS activity and mRNA decreased in SHHF, but mRNA was not significantly altered in humans. Cardiolipin remodeling enzymes, monolysocardiolipin acyltransferase (MLCL AT) and tafazzin, showed variable changes during HF. MLCL AT activity increased in SHHF. Tafazzin mRNA decreased in SHHF and human HF, but not in SD rats. The gene expression of acyl-CoA: lysocardiolipin acyltransferase-1, an endoplasmic reticulum MLCL AT, remained unaltered in SHHF rats. The results provide mechanisms whereby both cardiolipin biosynthesis and remodeling are altered during HF. Increases in CDS-1, PGPS, and MLCL AT suggest compensatory mechanisms during the development of HF. Human and SD data imply that similar trends may occur in human HF, but not during nonpathological aging, consistent with previous cardiolipin studies.     

Recombinant plasmid conferring proline overproduction and osmotic tolerance.

A recombinant plasmid carrying the proBA (pro-74) mutant allele which governs osmotic tolerance and proline overproduction was constructed by using the broad-host-range plasmid vector pQSR49. The physiological, biochemical, and genetic properties of strains carrying the pQSR49 derivatives pMJ101 and pMJ1, mutant and wild type, respectively, were investigated. pMJ101 conferred enhanced osmotolerance compared with strains carrying the wild type, pMJ1. These results are in contrast to those obtained previously with strains carrying recombinant plasmids based on pBR322 that failed to confer the osmotic tolerance phenotype. gamma-Glutamyl kinase (first step in proline biosynthesis) from strains carrying pMJ101 was 200-fold less sensitive to feedback inhibition than was the wild-type enzyme. As expected, the intracellular proline levels of strains carrying pMJ101 were more than an order of magnitude higher than those of the wild type. An analysis of copy number revealed that the pQSR49 constructs were present in the cell at a level six- to eightfold lower than those of the pBR322 recombinants, which may account for the difference in phenotype. We found that the genetic stability of the pQSR49 derivative in a variety of gram-negative bacteria was dependent on the insert orientation and the presence of foreign DNA on the plasmid. These factors may be significant in future studies aimed at expanding the osmotolerance phenotype to a broad range of gram-negative bacteria.     

Heliothrix oregonensis,gen. nov., sp. nov., a phototrophic filamentous gliding bacterium containing bacteriochlorophyll a

An unusual filamentous, gliding bacterium was found in a few hot springs in Oregon where it formed a nearly unispecific top layer of microbial mats. It contained a bacteriochlorophyll a-like pigment and an abundance of carotenoids. There were no chlorosomes or additional chlorophylls. The organism was aerotolerant and appeared to be photoheterotrophic. It was successfully co-cultured with an aerobic chemoheterotroph in a medium containing glucose and casamino acids. Although it has many characteristics in common with the genus Chloroflexus, the lack of chlorosomes and bacteriochlorophyll c and the aerobic nature of this organism indicate that it should be placed in a new genus. This conclusion is supported by 5S rRNA nucleotide sequence data.     

Inositol 1,4,5-trisphosphate (IP3) induced rapid formation of thromboxane B2 in saponin-permeabilised human platelets: mechanism of IP3 action

The mechanism of IP3-induced activation of saponin-permeabilised platelets has been examined. Saponin permeabilization resulted in the leakage of low-Mr substances into and from the cells without loss of cytoplasmic proteins. Addition of IP3 rapidly induced a dose-related formation of thromboxane B2 and release into the medium, leading to the responses of shape change, aggregation and [14C]5HT release. These responses were inhibited by the thromboxane A2 receptor antagonist AH23848. The IP3-induced release of 45Ca from intracellular stores was not affected by indomethacin. Synthesis of thromboxane was inhibited if Ca2+ elevation was prevented by using Ca-EGTA buffers during permeabilization. These studies indicate that IP3-induced activation was due to Ca2+ mobilisation leading to phospholipase activation and thromboxane synthesis.