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D Shemin

Publications and source records attributed to D Shemin.

35 records · Page 2Linked to original sources
PubMed1973

Synthesis of the pyrrole porphobilinogen by sepharose-linked -aminolevulinic acid dehydratase.

delta-Aminolevulinic acid dehydratase from Rhodopseudomonas spheroides was covalently linked to Sepharose 4B, which had been activated with cyanogen bromide. A column containing this enzyme gel readily catalyzed the synthesis of the pyrrole porphobilinogen on continuous passage of a solution of delta-aminolevulinic acid. Under the conditions of the procedures, product inhibition was minimized and a 50 to 94 percent yield was attained. A column containing about 1 milligram of enzyme was continuously operated for 27 days. Although its total activity appeared to be reduced about 30 percent at the end of this time, the bound enzyme produced approximately 200 milligrams of porphobilinogen each day, and about 5 grams of the pyrrole were isolated.

Binding Sites↗
PubMed1972

The biosynthesis of vitamin B 12 : a study by 13 C magnetic resonance spectroscopy.

The origin of the methyl group on C-1 of Ring A of the corrin ring of vitamin B(12) was investigated by (13)C magnetic resonance spectroscopy. The proton-decoupled (13)C spectra of vitamin B(12) synthesized from [5-(13)C]delta-aminolevulinic acid by Propionibacteria were obtained by Fourier-transform nuclear magnetic resonance of high resolution, and spectra of high-resolution proton magnetic resonance of the (13)C-labeled B(12) were also taken. The delta-carbon atom of delta-aminolevulinic acid is the source of seven or eight known positions of vitamin B(12), depending on whether the C-1 methyl group is also derived from the labeled substrate. We have found seven resonances whose chemical shifts enable us to identify the position of the (13)C atoms in the molecule from the assignment of Dodderell and Allerhand. We observed no (13)C resonance corresponding to the C-1 methyl group of Ring A. Furthermore, the proton magnetic resonance spectrum showed no spin-spin splitting of the proton peak at the tau values assigned for the H atoms in this methyl group. It would thus appear that the methyl group at C-1, which has been considered to have the same origin as the delta-methine bridge of porphyrins, does not originate from the delta-carbon atom of delta-aminolevulinic acid. This finding may aid in elucidation of the mechanism of synthesis of the functional isomer of vitamin B(12) and porphyrins. The (13)C-labeled vitamin B(12) enabled us to make further assignments to the (13)C magnetic resonance of the vitamin.

Carbon Isotopes↗
PubMed1969

Properties and characteristics of a bacteriocin from Serratia marcescens.

A strain of Serratia marcescens was found to produce a bacteriocin that inhibits the growth of certain Escherichia coli strains. This inhibition was bacteriocidal rather than bacteriostatic and was not caused by a bacteriophage. Whereas the bacteriocin was inactive on the 7 Serratia strains tested, it killed 11 of the 20 E. coli strains tested for sensitivity. A relationship of the bacteriocin to a possible colicin cannot as yet be excluded, although E. coli mutants resistant to 1 or 2 of 15 different colicins remained sensitive to the bacteriocin. The bacteriocidal effect by the bacteriocin could be interrupted in a substantial fraction of the treated cell population by the addition of trypsin. The synthesis of the bacteriocin was inducible by ultraviolet light or by starvation for thymidine. Both procedures led to a similar increase in maximum bacteriocin titer relative to noninduced cultures.

Bacteriocins↗
PubMed1969

Concomitant synthesis of bacteriocin and bacteriocin inactivator from Serratia marcescens.

We have found that Serratia marcescens strain P & S is bacteriocinogenic. However, the phenotypic expression of bacteriocin activity depends upon the temperature at which the cells are grown. When the organism is grown at 30 to 37 C, no bacteriocin activity can be demonstrated, whereas when it is grown at 39 C bacteriocin activity is readily observed. It appears that the P & S strain concomitantly synthesizes a bacteriocin and a substance which not only can inactivate the bacteriocin but also has a high activation energy for inactivation. This inactivator readily loses its activity when heated at 39 C for 1 hr. Two mutants were isolated from the P & S strain which can produce active bacteriocin when grown at temperatures from 30 to 39 C. It is significant that these mutants have considerably less bacteriocin inactivator. The data suggest that the inactivator is an extracellular protease. The ability of one of these mutants, JF58-12, to produce active bacteriocin at temperatures between 30 and 39 C is a stable property, whereas in the other mutant, JF48W, this property is unstable. JF48W was selected from the P & S strain in two steps: first a streptomycin-resistant variant (strain A-10) was isolated and from this mutant a strain (JF48W) was isolated which not only synthesized little of the inactivator but also did not synthesize the red pigmnet prodigiosin. This latter pleiotropic mutant appears to revert in one step to a phenotype similar to the P & S strain, since it is streptomycin-sensitive and produces prodigiosin and normal amounts of inactivator and the demonstration of bacteriocin activity is temperature-dependent.

Bacteriocins↗