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Biomedical subjects

L I Hecker

Publications and source records attributed to L I Hecker.

9 recordsLinked to original sources
PubMed1979

The mutagenicity of nitrosopyrrolidine is related to its metabolism.

Various cell fractions from rat liver were tested for their ability to convert nitrosopyrrolidine (NO-PYR) to products which were mutagenic to E. coli in liquid-incubation assays. Microsomes alone produced only a small number of tyr+ revertants, approximately 40/10(8) survivors), while the S100 supernatant produced none at all. However, the S8 Fraction or combinations of microsomes and the S100 supernatant, yielded 300-400 tyr+ revertants/10(8) survivors. Neither products of the microsomal, nor microsome + supernatant reactions were mutagenic in the absence or presence of cellular fractions. These results suggest that bacterial mutagens are formed during the microsomal metabolism of NO-PYR to 2-hydroxytetrahydrofuran by alpha-hydroxylation, but not during the metabolism of 2-hydroxytetrahydrofuran by the S100 supernatant enzymes. Possible roles of the supernatant enzymes in the formation of mutagenic intermediates during the initial alpha-hydroxylation of NO-PYR are discussed.

Animals↗
PubMed1979

Metabolism of the liver carcinogen N-nitrosopyrrolidine by rat liver microsomes.

This report represents a study of the total metabolism of the hepatocellular carcinogen, N-nitrosopyrrolidine (NO-PYR), by rat liver microsomes and postmicrosomal supernatant. [2,5-14C]NO-PYR, which is totally extractable from aqueous solution with methylene chloride, is converted to radioactive nonmethylene chloride-extractable products by these fractions. The initial rate of conversion to nonmethylene chloride-extractable products follows simple Michaelis-Menten kinetics with an apparent Km of 3.6 x 10(-4) M NO-PYR. The major products of NO-PYR metabolism by rat liver microsomes and postmicrosomal supernatant have been isolated and identified. One product of metabolism of NO-PYR is 2-hydroxytetrahydrofuran formed by alpha-hydroxylation by the microsomes. In the presence of postmicrosomal supernatant enzymes, this compound exists only as a transient intermediate which is rapidly converted to 1,4-butanediol or gamma-hydroxybutyrate. These compounds may be cycled into general cellular metabolism resulting in the production of CO2. Two minor pathways of metabolism have also been found.

Animals↗
PubMed1977

Cloned ribosomal RNA genes from chloroplasts of Euglena gracilis.

Fragments of Euglena chloroplast DNA generated by endonuclease R-Eco RI were separated by agarose-gel electrophoresis into 24 distinct bands. At least five fragments contain sequences complementary to chloroplast ribosomal RNA, Most of the Eco RI fragments have been cloned in a plasmid of Escherichia coli. Three of the cloned fragments were shown to contain chloroplast ribosomal RNA sequences by DNA-RNA hybridization.

Chloroplasts↗
PubMed1977

Nucleotide sequence of Neurospora crassa cytoplasmic initiator tRNA.

Initiator methionine tRNA from the cytoplasm of Neurospora crassa has been purified and sequenced. The sequence is: pAGCUGCAUm1GGCGCAGCGGAAGCGCM22GCY*GGGCUCAUt6AACCCGGAGm7GU (or D) - CACUCGAUCGm1AAACGAG*UUGCAGCUACCAOH. Similar to initiator tRNAs from the cytoplasm of other eukaryotes, this tRNA also contains the sequence -AUCG- instead of the usual -TphiCG (or A)- found in loop IV of other tRNAs. The sequence of the N. crassa cytoplasmic initiator tRNA is quite different from that of the corresponding mitochondrial initiator tRNA. Comparison of the sequence of N. crassa cytoplasmic initiator tRNA to those of yeast, wheat germ and vertebrate cytoplasmic initiator tRNA indicates that the sequences of the two fungal tRNAs are no more similar to each other than they are to those of other initiator tRNAs.

Amino Acyl-tRNA Synthetases↗