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Biomedical subjects

G Koch

Publications and source records attributed to G Koch.

At least 487 records · Page 27Linked to original sources
PubMed1975

Inhibition of initiation of protein synthesis in mammalian tissue culture cells by L-1-tosylamido-2-phenylethyl chloromethyl ketone.

Incorporation of amino acids into proteins in HeLa cells, virus-transformed 3T3 mouse fibroblasts, and mouse plasmacytoma cells is inhibited after the addition of L-1-tosylamido-2-phenylethyl chloromethyl ketone, an alkylating agent and chymotrypsin-specific protease inhibitor. Addition of this drug to tissue culture cells at concentrations of 20 to 30 mug per ml results in an irreversible inhibition of the incorporation of amino acids into cellular proteins, and a rapid and complete breakdown of polyribosomes. A comparative study examining the effects of L-1-tosylamido-2-phenylethyl chloromethyl ketone and several known inhibitors of in vivo protein synthesis, with known mechanisms of action, revealed that an optimal concentration of L-1-tosylamido-2-phenylethyl chloromethyl ketone: (a) immediately and selectively inhibits initiation of protein synthesis, (b) does not significantly affect normal elongation rates, and (c) does not promote a premature release of nascent peptides. L-1-Tosylamido-2-phenylethyl chloromenthyl ketone may prove to be a useful tool in investigating the initiatior of protein synthesis in eukaryotic cells.

Animals↗
PubMed1975

Poliovirus-induced infectious double-stranded RNA: Effect of RNA-degrading enzymes.

The infectivity of replicative form RNA (RF-RNA) isolated from poliovirus-infected HeLa cells is completely resistant to the action of T-1 RNase but decreases after exposure to RNase A in the presence of 0.3 M NaCl. Under these conditions neither enzyme produces single-stranded nicks in RF-RNA. Three endonuclease-free exonuleases (RNase II, polynucleotide phosphorylase and spleen phosphodiesterase) rapidly destroy the infectivity of single-stranded RNA, but do not alter the infectivity of RF-RNA. It is concluded that RF-RNA does not contain single-stranded ends essential for infectivity. Indirect evidence suggests that all or most of the poly A region at the 3' end of the plus strand of infectious RF-RNA is base-paired to a poly U region at the 5 end of the minus strand.

Base Sequence↗
PubMed1975

Effect of DEAE-dextran on protein synthesis in HeLa cells.

Concentrations of DEAE-dextran which are currently used to stimulate the interaction between animal cells and natural or synthetic polynucleotides, inhibit protein synthesis in HeLa cells. This inhibition results from the blocking of more than one of the steps in protein synthesis, including transport of amino acids. The results support the hypothesis that enhancement of cellular competence for infection by viral RNA involves interference with initiation of cellular protein synthesis.

Amino Acids↗
PubMed1975

Detection in HeLa cell extracts of a 7-methyl guanosine specific enzyme activity that cleaves m7GpppNm.

Extracts prepared from HeLa cells contain an enzymatic activity which cleaves m7G(5')ppp(5')Gm to m7pG and ppGm. The activity exhibits a high degree of substrate specificity and does not cleave G(5')ppp(5')G or the ring opened derivative of m7GpppGm which has lost the positive charge from the N7 position of m7G. m7GpppGm as the 5' terminal structure of intact reovirus mRNA is resistant to attack by the pyrophosphatase activity, but becomes partially sensitive in the 5' terminal fragment consisting of 7-10 nucleotides derived from the same mRNA by T1 RNAase digestion. m7G(5')ppp(5')GmpCp is completely sensitive to cleavage resulting in the release of m7pG without generation of m7GpppGm as an intermediate. These results establish the existence of a 7-methyl guanosine specific pyrophosphatase activity in HeLa cells.

Coliphages↗
PubMed1975

Selective blockage of initiation of host protein synthesis in RNA-virus-infected cells.

Poliovirus mRNA and mRNA transcribed from vesicular stomatitis virus and reovirus genomes efficiently direct protein synthesis in vivo under experimental conditions where the initiation of host protein synthesis is selectively blocked. The selective blockage of host peptide chain initiation after exposure to hypertonic medium indicates that the translation of viral mRNA is more efficiently initiated than is the translation of host mRNA. It further suggests that virus directed suppression of host protein synthesis could proceed by a mechanism involving a nonspecific decrease in the rate of peptide chain initiation. Exposure of infected cells to hypertonic medium provides a unique tool with which to study early events in the infectious cycle by permitting the efficient unmasking of virus-specific poly-peptide synthesis.

Animals↗
PubMed1975

Caries preventive effect of a fluoride-containing varnish (Duraphat) after 1 year's study.

The caries prophylactic effect of semi-annual applications of a fluoride-containing varnish (Duraphat) was tested in 121 15-year-old children. The children were divided into a test (60 subjects). The teeth of the children in the test group were coated with fluoride varnish at the beginning of the experimental period and again 6 months later. A clinical and radiographic examination of all children was performed immediately prior to the first application of varnish and 1 year later. The mean caries increment was 0.9 new DMFS in the test group and 4.0 in the control group. The difference was statistically significant at the 0.1% level. The caries prophylactic effect on different tooth surfaces was statistically significant both on proximal and on occlusal surfaces at the 0.1% level. Analyzing the material with respect to the caries prophylactic effect against the background of caries prevalence at the start of the investigation showed a better effect in the group of children with low and medium initial DMFS values.

Adolescent↗
PubMed1975

Caries frequency in children with controlled diabetes.

The frequency of caries was assessed in 33 diabetic children in whom the diabetes required insulin and dietary restriction and had been diagnosed before eruption of the permanent teeth. The frequency of caries and the number of erupted teeth were obtained from the dental records of the school dental service. Age- and sex-matched non-diabetic classmates served as controls. The mean number of DFS at the last dental examination of the diabetic children was 13.4, compared with 20.5 in the controls. The difference was largest in 12- to 14-year-old children, particularly in the premolar region, where the mean number of carious and filled surfaces in the diabetics was 2.6 compared with 5.9 in the controls. In all age groups, proximal carious lesions were less common in the diabetics than in the controls. No notable difference was found between the mean number of erupted teeth in the diabetics and that of the controls, except among the 12- to 14-year-old children. In that age group the diabetics had, on the average, 6.0 erupted premolars compared with 7.3 in the controls and 2.7 erupted permanent second molars compared with 3.5 in the controls. The results indicate that the dietary restriction observed by the diabetics had a favorable effect in promoting a lower caries frequency on all groups of teeth and on most tooth surfaces.

Adolescent↗
PubMed1975

Differential inhibition of vesicular stomatitis virus polypeptide synthesis by hypertonic initiation block.

Synthesis of the vesicular stomatitis virus membrane matrix protein and the glycoprotein is inhibited to a greater extent than the synthesis of the nucleocapsid protein, the nonstructural protein, and the large protein when the rate of peptide chain initiation is reduced by exposure of vesicular stomatitis virus-infected cells to hypertonic medium. It is concluded that the relative sensitivity of individual viral polypeptide synthesis to hypertonic initiation block is independent of the site of synthesis, i.e., whether on membrane-associated or free polyribosomes.

Animals↗