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R Bass

Publications and source records attributed to R Bass.

At least 73 records · Page 4Linked to original sources
PubMed1977

Embryonic development and mitochondrial function. 2. Thiamphenicol induced embryotoxicity.

Inhibition of mitochondrial protein synthesis in rat embryos during late organogenesis leads to impaired embryonic development. 1. Thiamphenicol (TAP), similar to chloramphenicol, inhibits in vivo the synthesis of cytochrome oxidase (cytox), which is partially synthesized by the mitochondrion. Subsequently, DNA synthesis and embryonic growth are affected. 2. Embryos on day 10 and 11, in contrast to embryos on day 9 of gestation, show a high sensitivity of mitochondrial protein synthesis, measured as cytox activity. From day 10 onwards, such an inhibition leads to pronounced impairment of DNA synthesis. The rat hemochorial placenta starts functioning on day 12 of gestation. Larger doses of TAP are required to inhibit cytox and DNA synthesis for treatment after placentation rather than before placentation. 3. Dose-response relationships differ depending on the date and duration of treatment. Application of TAP for 1 day requires 10-30 mg/kg TAP to inhibit cytox synthesis and 60-100 mg/kg to impair embryonic growth. Prolongation of treatment to 4 days (day 10-13) lowers the dose required for inhibition of DNA synthesis to 10 mg TAP/kg/day. This is lower than the human therapeutic dose. Larger doses lead to embryolethality. 4. The extent of inhibition of DNA synthesis provoked by inhibition of mitochondrial protein synthesis depends on a number of factors which include: different growth rates during organogenesis, the number of mitochondria present prior to treatment, availability of extramitochondrial ATP sources and placental permeability barrier.

Animals↗
PubMed1976

The site for catabolite deactivation in the L-arabinose BAD operon in Escherichia coli B/r.

A series of deletions beginning in the leu operon and continuing into the araC gene and also into the ara controlling site region were analyzed in reciprocal merodiploids, e.g., F' A2Cc67/B24delta719, F' B24delta719/A2Cc67, for their effects on catabolite deactivation (CD). The results of these experiments are consistent with placing the catabolite gene activator-cyclic AMP sensitive site in the controlling site region between araB and araO. With a deletion mutant, delta1109, that places araBAD under leu control when transcription begins at leuP, the araBAD operon is immune to CD even though araCGA, araP and araI are intact and functional. To focus attention on the fine structure and related functions of this region we propose that the three proteins that function therein have separate sites of action: araI (initiator-site for activator), araP (promoter-site for RNA polymerase) and ara(CGA) (catabolite gene activator-site for CGA-cAMP). None of the eighteen initiator constitutive mutants (Ic) tested have any significant effect on catabolite derepression or on the maximal level of expression of the operon supporting the view that the araI site may be distinct from araP and ARA(CGA). A series of constitutive mutants in the araC gene (Cc) also have no pronounced effect on catabolite deactivation.

Arabinose↗
PubMed1976

Inhibition of the growth of mammalian cells in cuture by amino acids and the isolation and characterization of L-phenylalanine transport.

Raising the concentration of phenylalanine and other amino acids in MEM leads to the inhibition of growth and in some cases to death of A9. Balb 3T3 , SV40 Balb 3T3 (SVT2), CHO, and WI38. All cells tested exhibited some similar senstivities to certain of the amino acids. but there were some unique differences. Phenylalanine-resistant mutants (Pher) of A9 were isolated that had modified phenylalanine-transport properties. These mutants can be isolated by a single-step selection procedure. A Lineweaver-Burk plot of initial rates of phenylalanine uptake by A9 and mutants showed a biphasic curve suggesting two transport systems. The Pher mutants had altered properties of both systems. It is suggested that the selection of clones resistant to high concentration of several of the natural amino acid may be used as a general method for the isolation of mutants affecting the various amino acid transport systems in mammalian cells.

Amino Acids, Essential↗
PubMed1976

Mutations affecting catabolite repression of the L-arabinose regulon in Escherichia coli B/r.

Expression of the L-arabinose regulon in Escherichia coli B/r requires, among other things, cyclic adenosine-3', 5'-monophosphate (cAMP) and the cAMP receptor protein (CRP). Mutants deficient in adenyl cyclase (cya-), the enzyme which synthesizes cAMP, or CRP (crp-) are unable to utilize a variety of carbohydrates, including L-arabinose. Ara+ revertants of a cya-crp- strain were isolated on 0.2% minimal L-arabinose plates, conditions which require the entire ara regulon to be activated in the absence of cAMP and CRP. Evidence from genetic and physiological studies is consistent with placing these mutations in the araC regulatory gene. Deletion mapping with one mutant localized the site within either araO or araC, and complementation tests indicated the mutants acted trans to confer the ability to utilize L-arabinose in a cya-crp- genetic background. Since genetic analysis supports the conclusion, that the mutant sites are in the araC regulatory gene, the mutants were designated araCi, indicating a mutation in the regulatory gene affecting the cAMP-CRP requirement. Physiological analysis of one mutant, araCi1, illustrates the trans-acting nature of the mutation. In a cya-crp- genetic background, araCi1 promoted synthesis of both isomerase, a product of the araBAD operon, and permease, a product of the araE operon. Isomerase and permease levels in araCi1 cya+ crp+ were hyperinducible, and the sensitivity of each to cAMP was altered. Two models are presented that show the possible mutational lesion in the araCi strains.

Adenylyl Cyclases↗
PubMed1975

Chloramphenicol/thiamphenicol and cycloheximide as tools for the measurement of mitochondrial protein synthesis in vitro during organogenesis of rat embryos.

1. A test system was developed to allow the measurement of protein synthesis in vitro in mitochondria from tissues which were accessible only in small quantities. The subcellular fractions which could be isolated are not purely mitochondrial but contain other particles as well, mainly microsomal, which are also active in protein synthesis. The following differences between mitochondrial and microsomal protein synthesis in vitro were used to measure selectively the mitochondrial portion in cell fractions sedimenting between 600 and 10000 X g: selective inhibition of mitochondrial protein synthesis by chloramphenicol/thiamphenicol selective inhibition of microsomal protein synthesis by cycloheximide kinetics of amino acid incorporation a medium favoring mitochondrial protein synthesis Activity of mitochondrial protein synthesis was based on measurements of cytochrome oxidase, a mitochondrial marker enzyme. 2. The technique developed was used for the evaluation of mitochondrial protein synthesis in mammalian embryonic tissues. It may equally well be applied to other tissues available in small amounts and in cases where the isolation of highly purified mitochondrial fractions is met with difficulty. 3. Comparing the rate of 14C-phenylalanine incorporation into mitochondrial protein from rat embryos at different stages of gestation, it was found that mitochondria from 11=day-old rat embryos exhibit an approximately 30-fold higher capacity for protein synthesis than those of day 13-16. On day 12 the capacity is 6 times higher than on the following days.

Animals↗
PubMed1975

Embryonic development and mitochondrial function. 1. Effects of chloramphenicol infusion on the synthesis of cytochrome oxidase and DNA in rat embryos during late organogenesis.

Cytochrome oxidase, which is partially synthesized by the mitochondrion, was used as a measure for the development of mitochondrial function in rat embryos during the late stage of organogenesis. For this purpose the specific inhibitor of mitochondrial protein synthesis, chloramphenicol (CAP), served as a tool. Due to the rapid elimination rate of CAP from rats, a method for continuous infusion which would not cause immobilization to the animals was devised. 1. Pharmacokinetic studies proved that CAP reaches the embryo before placentation. Concentrations of CAP in the embryo are as high as they are in the maternal serum (about 20 mug/ml serum or g embryo) and thuse are sufficiently in supply for the inhibition of mitochondrial proteins synthesis, if 1000 mg/kg CAP are infused intravenously per 24 hrs. CAP is partially excluded from the embryonic compartment after the placental barrier has fully developed: whereas CAP concentration in the maternal serum remains at about 20 mug/ml, the concentration in the embryonic compartment drops to about 10 mug/g embryonic tissue during day 13 of gestation. 2. The average cytochrome oxidase activity per cell is very low (about 1 nmole O2/min X mug DNA-1) in embryonic tissue as it is in many other rapidly proliferating tissues. It is 15-60 times higher in slowly proliferating tissues, as, for example, the adult rat liver or brain (greater than 14 nmoles O2/min X mug DNA-1). 3. When the infusion technique is applied on day 12 of gestation, a sufficiently high concentration of CAP in embryonic tissue can be obtained to inhibit the synthesis of cytochrome oxidase. In constrast to tissues of an adult organism-as in the case of liver after partial hepatectomy- in embryonic tissues this limitation in the availablity of cytochrome oxidase appearently results in a critical reduction of energy production, which subsequently affects the DNA synthesis and embryonic growth. 4. The possible relevance and applicability of these experimental findings to man is discussed.

Animals↗