Puromycin

Puromycin. Puromycin (19), elaborated by S. alboniger (1—4), inhibits protein synthesis by replacing aminoacyl-tRNA at the A-site of peptidyltransferase (48,49). Photosensitive analogues of (19) have been used to label the A-site proteins of peptidyltransferase and tRNA (30). Compound (19), and its carbocycHc analogue have been used to study the accumulation of glycoprotein-derived free sialooligosaccharides, accumulation of mRNA, methylase activity, enzyme transport, rat embryo development, the acceptor site of human placental 80S ribosomes, and gene expression in mammalian cells (51—60). 

Antibiotic A201A. Antibiotic A201A (23), produced by S. capreolus is an /V -dimethyladenine nucleoside stmcturaHy similar to puromycin (19). Compound (23) which contains an aromatic acid and monosaccharide residues (1,4), inhibits the incorporation of amino acids into proteins but has no effect on RNA or DNA synthesis. Compound (23) does not accept polypeptides as does (19), and does appear to block formation of the initiation complex of the SOS subunit. It may block formation of a puromycin-reactive ribosome. 

One type of fatty liver that has been smdied extensively in rats is due to a deficiency of choline, which has therefore been called a lipotropic factor. The antibiotic puromycin, ethionine (a-amino-y-mercaptobu-tyric acid), carbon tetrachloride, chloroform, phosphorus, lead, and arsenic all cause fatty liver and a marked reduction in concentration of VLDL in rats. Choline will not protect the organism against these agents but appears to aid in recovery. The action of carbon tetrachloride probably involves formation of free radicals... 

Figure 38-11. The comparative structures of the antibiotic puromycin (fop) and the 3 terminal portion of tyrosinyl-tRNA (bottom).

Other antibiotics inhibit protein synthesis on all ribosomes (puromycin) or only on those of eukaryotic cells (cycloheximide). Puromycin (Figure 38—11) is a structural analog of tyrosinyl-tRNA. Puromycin is incorporated via the A site on the ribosome into the carboxyl terminal position of a peptide but causes the premature release of the polypeptide. Puromycin, as a tyrosinyl-tRNA analog, effectively inhibits protein synthesis in both prokaryotes and eukaryotes. Cycloheximide inhibits peptidyltransferase in the 60S ribosomal subunit in eukaryotes, presumably by binding to an rRNA component. 

Many of these compounds—puromycin and cycloheximide in particular—are not cfinically useful but have been important in elucidating the role of protein synthesis in the regulation of metabolic processes, particularly enzyme induction by hormones. 

C22H34N12O10Pt2+-1.5 Cl- 0.5 I--2 H20 ranosyl]-6-(dimethylamino)purine, dihydrochloride, pentahydrate (puromycin, dihydrochloride, pentahydrate) Ethylenediamine-bis(guanosine) platinum(II), chloride, EGUOSP 34 375... 

Puromycin. Synthetic Studies. XIII. Synthesis of 6-Dimethylamino-... 

Nemoto, N., Miyamoto-Sato, E., Husimi, Y. and Yanagawa, H. (1997) In vitro virus bonding of mRNA bearing puromycin at the 3 -terminal end to the C-terminal end of its encoded protein on the ribosome in vitro. FEBS Letters, 414, 405 408. 

Comment A simple test that is often done is to treat the lysate with 30 fiM EDTA prior to loading on the gradient, which leads to the disassembly of polysomes due to chelation of Mg2+ (Fig. 6.4B). EDTA is, however, not a very specific reagent and instead more specific drugs such as puromycin, which causes polypeptide chain termination and disaggregates polysomes, may be used. 

The antagonistic properties of FR 900452 have also been examined in a model of endotoxin shock, the haemodynamic and haematological manifestations of this condition closely resembling the changes induced by PAF. FR 900452 (10 mg/kg, i.v.) almost completely prevents PAF (1 /ig/kg, i.v.)-induced thrombocytopenia and leukocytopenia in rabbits [295]. It also significantly inhibits endotoxin (E. coli LPS, 30 /ig/kg, i.v.)-induced thrombocytopenia but not leukocytopenia. The same dose of FR 900452 also causes the decreased arterial blood pressure to return to normal in the endotoxin-induced rat hypotension model, an effect also reported for other PAF inhibitors [121, 274], Finally, FR 900452 has been tested for its therapeutic effect on rat nephrosis induced by aminonucleoside (puromycin, 100 mg/kg, i.p.). At 100 mg/kg twice a day orally for 6 days, the agent significantly reduces urinary protein loss in nephrotic rats [298]. 

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