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Biomedical subjects

F Lipmann

Publications and source records attributed to F Lipmann.

At least 73 records · Page 4Linked to original sources
PubMed1970

Mechanism of activation by adenosine 3':5'-cyclic monophosphate of a protein phosphokinase from rabbit reticulocytes.

Two protein phosphokinases (EC 2.7.1.37) were found to be present in rabbit reticulocytes. The two enzymes were separated by DEAE-cellulose chromatography and called kinases I and II. Adenosien 3':5'-cyclic monophosphate stimulated the activity of both enzymes. However, the degree of stimulation was different and depended on the protein acceptor used. In the presence of adenosine 3':5'-cyclic monophosphate, protein kinase I dissociated into two subunits: a subunit binding adenosine 3':5'-cyclic monophosphate, and a catalytic subunit. The component binding the cyclic nucleotide appeared to act as an inhibitory protein, regulating the activity of the catalytic subunit. The mechanism of action of the cyclic nucleotide on kinase II appeared to be different from that of kinase I.

Adenine Nucleotides↗
PubMed1969

Einar Lundsgaard.

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Biochemistry↗
PubMed1969

Fusidic acid: inhibition of factor T2 in reticulocyte protein synthesis.

The steroid antibiotic fusidic acid inhibits reticulocyte protein synthesis. This inhibition appears to be due to interference with the activity of the T(2) supernatant fraction, and strengthens the proposition that T(2) is functionally analogous to the G-factor of bacterial protein synthesis, which is also specifically inhibited by this antibiotic.

Adenosine Triphosphate↗
PubMed1969

Interrelation between activation and polymerization in gramicidin S biosynthesis.

The nucleic acid-independent biosynthesis of the peptide antibiotic gramicidin S results from the interaction of an enzyme bearing phenylalanine in activated form with a polyenzyme system charged with the other four component amino acids. After reaction with ATP, magnesium, and any or all of its amino acid substrates, the polyenzyme system (mol wt 280,000) yields complexes containing AMP and the respective amino acids in the proportion of 1 to 2. Similar complexes are formed by another enzyme (mol wt 100,000) on incubation with ATP, magnesium, and L- or D-phenylalanine. The amino acids are probably bound as aminoacyl adenylates and then transferred to another function on the enzyme. Initiation of polymerization is achieved by combination of the two complexes. No ATP is needed for completion of synthesis, and free intermediates are not released. Enzyme organization and specificity are responsible for the ordering of the amino acid sequence.

Adenosine Triphosphate↗
PubMed1969

Isolation of adenyl cyclase from Escherichia coli.

We have found a soluble cyclase, using for assay radioactively marked ATP as precursor. The reaction product was isolated by thin-layer chromatography and identified by specific degradation. After homogenization, part of the activity remained in the particulate fraction but could be easily extracted. The cyclase was concentrated 100-fold by conventional methods. The enzyme has a Mg(++) requirement and is inhibited by fluoride and inorganic pyrophosphate.

Adenine Nucleotides↗
PubMed1969

Peptidyl transfers in gramicidin S bisoynthesis from enzyme-bound thioester intermediates.

The biosynthesis of the peptide antibiotic gramicidin S involves successive peptidyl transfer reactions between intermediates bound in thioester linkages to two active enzyme fractions, I and II. Fraction II activates and recemizes phenylalanine, and then initiates peptidyl transfer by catalyzing a reaction between the carboxyl group of D-phenylalanine, bound to an enzymic sulfhydryl group, and the free imino group of L-proline, one of four L-amino acids all linked by their carboxyl functions to separate sulfhydryl groups on fraction I. Successive reactions of this type in the active centers of the multienzyme complex of fraction I lead to the formation of thioester-bonded nascent peptide chains and, ultimately, of the antibiotic product.

Amino Acid Sequence↗
PubMed1969

A stimulation by cyclic 3',5'-adenosine monophosphate of amino acid activation and polymerization in reticulocyte hemolysates.

With reticulocyte supernatant, cyclic 3',5'-adenosine monophosphate at concentrations of 10(-3) to 10(-2)M causes stimulation of aminoacyl-tRNA synthetases for some, e.g., valine and leucine, but not all, amino acids; it is highest at nonsaturating concentrations of ATP. Similar concentrations of cyclic 3',5'-adenosine monophosphate are found to stimulate phenylalanine polymerization from phenylalanyl transfer ribonucleic acid on polyuridylic acid-charged reticulocyte ribosomes. The degree of stimulation is highest at low GTP concentrations. It is abolished by addition of phosphoenolpyruvate + pyruvate kinase, which stimulate similarly or more effectively at low GTP levels. Under the conditions of these experiments, cyclic 3',5'-adenosine monophosphate did not appreciably inhibit GTP hydrolysis.

Adenine Nucleotides↗