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Biomedical subjects

D Richter

Publications and source records attributed to D Richter.

At least 397 records · Page 22Linked to original sources
PubMed1977

Gene expression in mitochondria and bacteria.

Mitochondria and bacteria possess protein synthesizing machineries which are similar in many respects; The regulation of gene expression in mitochondria is unknown. We, therefore, tried to use a well-established prokaryotic regulatory system for the exploration of mitochondrial gene regulation. DNA of the bacterial virus can be used as a template for gene expression in a mitochondrial in vitro system. The gene directed enzyme synthesis in the mitochondrial system is the basis for a study of regulation in mitochondrial protein synthesis.

Chloramphenicol↗
PubMed1977

[Localization of monoamine oxidase (MAO) in the brain of Periplaneta americana (L.) (author's transl)].

A DA-oxidizing MAO has been demonstrated histochemically in DOPAminergic synaptic areas in the brain of the cockroach (Periplaneta americana). However, a 5-HT-oxidizing MAO seems to be absent. The optimal temperature is 37 degrees C, the optimal pH is 7,6. After an abdominal injection the used MAO-inhibitors have no influence on the activity of the MAO. In adding pargyline to the incubating medium there is an inhibition.

Animals↗
PubMed1976

Stringent factor from Escherichia coli directs ribosomal binding and release of uncharged tRNA.

Uncharged tRNA is preferentially bound to the peptidyl site of the ribosome in the absence of stringent factor ,but in its presence is directed to the acceptor site. The synthesis of pppGpp and ppGpp is initiated by tRNA bound in the acceptor but not in the peptidyl site. In this reaction, tRNA is not permanently attached to the acceptor site. Uncharged [32P] tRNA but not 3H-labeled stringent factor is released from the ribosome after each round of stringent factor-dependent hydrolysis of ATP. ATP-32PPi-exchange experiments reveal that exchange is independent of the presence of GTP but strongly enhanced by the addition of stringent factor and tRNA. The tRNA release is suppressed when ATP is replaced by beta, gamma-imido adenosine 5'-triphosphate, 5'-AMP, or GTP.

Adenosine Triphosphate↗
PubMed1976

Free 3'-OH group of the terminal adenosine of the tRNA molecule is essential for the synthesis in vitro of guanosine tetraphosphate and pentaphosphate in a ribosomal system from Escherichia coli.

tRNAPhe from yeast modified at the 3'-terminal adenosine residue or missing part of its CpCpA end was investigated for its ability to participate in the synthesis of guanosine tetraphosphate and pentaphosphate using Escherichia coli ribosomes. Only tRNA containing complete CpCpA end and an intact ribose residue in the terminal adenosine was active in this process. The absence of the 2'-hydroxyl group of the terminal adenosine does not influence the reaction, but the 3'-hydroxyl group is essential and cannot be replaced by an amino group or a hydrogen atom. tRNA in which the 3'-terminal adenosine is replaced by formycin is active in the induction of guanosine tetraphosphate and pentaphosphate synthesis, but the reaction proceeds relatively slowly.

Adenosine↗
PubMed1976

The stringent control mechanism. Binding of uncharged tRNA and stringent factor to Escherichia coli ribosomes.

The mechanism of the interaction of uncharged tRNA and stringent factor with the ribosomes during the in vitro synthesis of guanosine polypnophates (pppGpp and ppGpp) was studied. 70S ribosomes lacking proteins L7 and L12 were able to bind radioactive stringent factor but not EF-Tu or EF-G. In addition, ribosomes carrying EF-Tu, GMPPCP and Phe-tRNA bound as much stringent factor as 70S ribosomes alone. This evidence suggests that the stringent and elongation factors recognize nonidentical site (s) on the ribosomes. When a 70S - poly U - tRNA complex was formed in the absence of stringent factor and was subsequently incubated with Nac-Phe-tRNA or Phe-tRNA only the binding of Nac-Phe-tRNA to the complex was inhibited. However, when the 70S-poly U-tRNA complex was formed in the presence of stringent factor and then was incubated with Nac-Phe-tRNA or Phe-tRNA only the binding of Phe-tRNA was inhibited. These results indicate that the stringent factor directs uncharged codon-specific tRNA into the acceptor site of the ribosome.

Binding Sites↗
PubMed1975

Escherichia coli stringent factor binds to ribosomes at a site different from that of elongation factor Tu or G.

The binding of Escherichia coli stringent factor to ribosomes has been studied; the reaction depends on 50S and 30S ribosomal subunits and poly(U) as messenger RNA. The ribosome-stringent factor complex is formed at 5-10 mM magnesium acetate; NH4 ions are inhibitory. Binding of the stringent factor to the 70S-mRNA complex is not stimulated by uncharged tRNA. The ribosomal binding site(s) for the stringent factor does not overlap with the one known for the elongation factor Tu (EF-Tu) or G (EF-G). Ribosomes carrying either EF-Tu or EF-G are active in binding the stringent factor; however, they are inactive in synthesizing guanosine 5'-triphosphate 3'-diphosphate (pppGpp) and guanosine 5'-diphosphate 3'-diphosphate (ppGpp). The latter result is due to the blockage of the ribosomal acceptor site by the aminoacyl-tRNA and/or elongation factors. That stringent and elongation factors do not compete for identical ribosomal region(s) is supported by: (1) the reverse experiments where ribosomes charged with the stringent factor are fully active in EF-Tu or EF-G dependent functions; (2) ribosomes that lack the two ribosomal proteins L7 and L12 known to be essential for EF-Tu and EF-G functions bind the stringent factor and are active in synthesizing pppGpp and ppGpp.

Binding Sites↗
PubMed1975

Isolation and characterization of two acidic proteins of 60s ribosomes from Artemia salina cysts.

60S ribosomes from encysted gastrulae of the brine shrimp Artemia salina contain two acidic proteins, which are homologous to the Escherichia coli proteins L7 and L12. The proteins were purified and characterized with respect to molecular weight, amino-acid composition, peptide maps, and their functional requirement in the elongation factor dependent binding of aminoacyl transfer RNA to the ribosome.

Amino Acids↗
PubMed1975

[Effect of organophosphorus compounds on esterases in rat intestine- a comparing histochemical and biochemical investigation (author's transl)].

The effect of 5 organophosphorus pesticids on the rat intestine and serum was investigated with histochemical and biochemical methods. The results of both methods were corresponding in nonspecific esterases of rat intestine. They differ in cholinesterases. Furthermore the effect on serum esterases of rat and man was investigated. With few exceptions the results corresponded too. We concluded, that the intestine is a suitable object for testing antiesterase action histochemically. General statements about total toxicity of a pesticid, however, are not possible.

Animals↗