Protein synthesis inhibitors sensitivity

The response of intestinal calcium transport to vitamin D is sensitive to the pretreatment by actinomycin However, it is unclear whether actinomycin D blocks the intestinal response to 1,25-(OH)2D3 There is some evidence which suggests that the lifetime of the 25-OH-D3-l-hydroxylase and its messenger is sufficiently short that the apparent block in vitamin D action on intestinal calcium transport may be due to the decay of the messenger and of the enzyme for the 1-hydroxylation reaction in the kidney Once the 1-hydroxylase is bypassed by the administration of 1,25- OH)2D3, actinomycin D does not block the transport process in the rat at least This finding has been confirmed and extended " Tsai et al. have provided conflicting evidence in the chick that actinomycin D does block the intestinal response to 1,25-(OH)2D3 However, they found it necessary to administer the actinomycin D every 2 hr before a block could be effected. Whether this is a bona fide block or a toxic reaction to the antibiotic remains undetermined. In any case the use of RNA and protein synthesis inhibitors in vivo to deduce the mechanism of action of 1,25-(OH)2D3 results in unclear and difficult to interpret results, especially if RNA and protein synthesis is incompletely blocked ... 

The mitochondrial ribosomes of mammals are small (about 555) and insensitive to erythromycin and lincomycin, although these antibiotics penetrate freely into the mitochondria. These ribosomes are sensitive to chloramphenicol which, fortunately, does not normally penetrate into mammalian mitochondria. Chloroplasts have ribosomes that are sensitive to most of the protein synthesis inhibitors that injure bacteria (Kiintzel and Noll, 1967). 

The existence of mitochondrial protein synthesis in S. pombe is indicated by the specific inhibition of growth on glycerol—but not on glucose— by mitochondrial protein-synthesis inhibitors. Antimycin-sensitive respiration and the absorption peaks of cytochromes aa and disappear in cells grown at pH 6.5 in glucose media supplemented with either 10 Mg ethidium bromide, 20 Mg of acriflavin, or 2 mg/ml chloramphenicol. ... 

Chlamydomonas reinhardi is sensitive to the protein synthesis inhibitor, erythromycin. At the time, some erythromycin-resistant strains had been isolated and described, and we were considering experimental approaches to locate the sites of structural genes for proteins of plastid ribosomes. It seemed reasonable to use erythromycin resistance as a genetic marker if we could be certain that the antibiotic interacts with some part of the chloroplast ribosome and was not lethal for some other reason. Erythromycin was known to bind to the large subunit of Escherichia coli ribosomes, and the alteration leading to resistance in the bacteria was found to reside in a single protein in the 50 S subunit. ... 

In A. vinelandii, C-terminal cleavage occurs in crude extracts after restoration of nickel and requires hours rather than minutes, as is the case in vivo. It does not require de novo protein synthesis and surprisingly is not redox or O2 sensitive. Also, it is not inhibited by well-established inhibitors of metallo- or serine protease families (Menon and Robson 1994). 

Mechanism of Action of Florfenicol. The inhibitory activities of chloramphenicol (1, R = NCh). thiamphenicol (1, R = SO2CH3), and florfenicol (2) against a sensitive E cofi strain have been studied. In two different liquid media, both chloramphenicol and florfenicol allowed only 20-30% residual growth at a drug concentration of 2 mg/L, whereas a thiaiuplieiiicul concentration of 25 mg/L was required to produce a similar effect. Florfenicol was also found to be a selective inhibitor of prokaryotic cells. At concentrations of 1 mg/L chloramphenicol and florfenicol, and at a concentration of 25 mg/L, thiamphenicol, inhibited protein synthesis. 

HF pyridine complex in methanol or THF is commonly used for the removal of TBS ethers. With acid- and base-sensitive substrates, the reaction can be buffered with additional pyridine.65 At a late stage in the synthesis of Calyculin A, a potent protein phosphatase inhibitor, a primary TBS ether was cleaved selectively in the presence of three secondary TBS ethers by using HF pyridine complex in THF-pyridine [Scheme 4.43].66... 

Fig. 10. Cell-free synthesis of t-PA glycoforms. The niRNA coding for t-PA was translated in a rabbit reticulocyte lysate in the presence of dog pancreas microsomes. Microsonies were isolated posttranslationally and the translocated, glycosylated products were separated by SDS-PAGE. Translation was carried out under conditions that either prevented (lane 2) or allowed (lane 3) proper folding of the t-PA molecule, yielding enzymatically active protein that was sensitive to natural inhibitors and stimulators.

Resistance to tetracyclines. The tetracyclines Figure 7.3) are a family of closely related antibiotics now numbering at least seven, which are inhibitors of protein synthesis [150]. The tetracyclines are broad spectrum antibiotics, oxytetracycline being the most active against strains of Ps. aeruginosa. In sensitive strains, the range of minimum inhibitory concentrations (MIC values) is 10-30 /xg/ml. However, strains with MIC values of greater than lOp-g/ml are considered clinically resistant. 

The answer is c. (Murray, pp 452—467. Scriver, pp 3—45. Sack, pp 1—40. Wilson, pp 101-120.) Prokaryotic ribosomes have a sedimentation coefficient of 70S and are composed of SOS and 30S subunits. Eukaryotic cytoplasmic ribosomes, either free or bound to the endoplasmic reticulum, are larger—60S and 40S subunits that associate to an SOS ribosome. Nuclear ribosomes are attached to the endoplasmic reticulum of the nuclear membrane. Ribosomes in chloroplasts and mitochondria of eukaryotic cells are more similar to prokaryotic ribosomes than to eukaryotic cytosolic ribosomes. Like bacterial ribosomes, chloroplast and mitochondrial ribosomes use a formylated tRNA. In addition, they are sensitive to many of the inhibitors of protein synthesis in bacteria. 

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