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Biomedical subjects

A L Demain

Publications and source records attributed to A L Demain.

At least 199 records · Page 11Linked to original sources
PubMed1971

Porphyrin overproduction by Pseudomonas denitrificans: essentiality of betaine and stimulation by ethionine.

Ethionine supplementation of a defined medium for growth of Pseudomonas denitrificans inhibited vitamin B(12) overproduction and led to the elaboration of a red pigment. The pigment was shown to be coproporphyrin III. Inhibition by ethionine of cobalamin synthesis is probably due to interference of methylation of the corrin nucleus by methionine. Accumulation of coproporphyrin III is thought to result from interference by ethionine with the activity of methionine in the coproporphyrinogenase reaction; this would inhibit formation of heme, the feedback inhibitor and corepressor of delta-aminolevulinate synthetase, thus allowing unregulated synthesis of coproporphyrinogen III and its degradation product, coproporphyrin III. Betaine, known to be required for vitamin B12 overproduction, was found to be an essential requirement for porphyrin overproduction in the presence of ethionine. Low-level production of porphyrin, which occurs in the absence of ethionine, also required betaine supplementation. Betaine is thus required for overproduction of both corrins and porphyrins in P. denitrificans.

Absorption↗
PubMed1970

Product inhibition of the fermentative formation of glutamic acid.

The addition of penicillin to cells of Corynebacterium glutamicum growing in 5-liter fermentors initiated the excretion of glutamic acid. The rate of glutamate production in fermentors declined continuously with time and reached 75% of the initial rate in 24 hr after penicillin had been added. The addition of glutamate to resting cell suspensions had only a slight effect on sugar utilization but caused a marked decrease in glutamate excretion. It is suggested that the high level of glutamate accumulating in the fermentation broth is responsible for inhibiting its own production.

Corynebacterium↗
PubMed1969

Glucose-6-phosphate dehydrogenase and its deficiency in mutants of Corynebacterium glutamicum.

Corynebacterium glutamicum is a member of a group of taxonomically related glutamate-excreting bacteria which utilize glucose both by the Embden-Meyerhof and the pentose phosphate pathways, the latter sequence accounting for 10 to 38% of the glucose metabolized. Some of the properties of glucose-6-phosphate dehydrogenase in crude extracts of C. glutamicum were studied. The enzyme was rapidly inactivated by dilution in tris (hydroxymethyl)aminomethane-hydrochloride buffer. This inactivation was prevented by the presence of 0.45 m NaCl. Mg(++) was required for enzyme activity, but Mn(++), Ca(++), Sr(++), and Ba(++) were equally effective. Growth of the organism under differing conditions did not markedly affect the specific activity of the enzyme. A generally applicable method for detecting colonies deficient in glucose-6-phosphate dehydrogenase was developed. Mutants so obtained were found to be auxotrophic for tryptophan. Upon reversion of the tryptophan requirement, the revertants still retained the property of glucose-6-phosphate dehydrogenase deficiency. Neither the mutants nor the revertants could grow as rapidly as the parent culture in glucose, in gluconate, or in a complex medium.

Buffers↗
PubMed1968

Dependence of diaminopurine utilization on the mutational site of purine auxotrophy in Bacillus subtilis. 1. Nutritional experiments.

An attempt was made to explain the puzzling observation that in bacteria 2,6-diaminopurine can replace guanine for guanineless mutants and for xanthineless mutants (both of which can make adenosine monophosphate de novo) but not for nonexacting purine auxotrophs (which cannot make adenosine monophosphate de novo). The analogue failed to inhibit the growth of nonexacting purineless Bacillus subtilis MB-1356 growing on guanine. In fact, growth was somewhat stimulated. This eliminated a possible solution involving the inhibition of guanosine monophosphate reductase by a diaminopurine derivative. Sparing of guanine by diaminopurine was matched by an even greater sparing of adenine. Addition of a small amount of adenine to MB-1356 failed to allow unrestricted growth on diaminopurine, thus eliminating a possible solution requiring an adenine derivative for the initial deamination of diaminopurine to guanine. The same degree of sparing of adenine by diaminopurine was observed whether both purines were added together or whether the adenine was added 1 hr after diaminopurine. This eliminated the possibility that diaminopurine was wasted by a "dead-end" conversion in the absence of adenine. Consideration of these nutritional data led to the development of two additional explanations, which are examined by tracer methodology in the following paper.

Adenine↗
PubMed1968

Dependence of diaminopurine utilization on the mutational site of purine auxotrophy in Bacillus subtilis. II. Tracer experiments.

Tracer experiments were carried out in an attempt to explain why guanineless auxotrophs can use diaminopurine as a guanine replacement but nonexacting purine auxotrophs cannot do so. Cell suspensions of the nonexacting purineless Bacillus subtilis MB-1356 incorporated more radioactivity from diaminopurine-2-(14)C into nucleic acid than did guanineless B. subtilis MB-1517. The radioactivity in MB-1356 ribonucleic acid (RNA) was distributed in both adenine and guanine nucleotides, thus eliminating the possibility that the deamination of diaminopurine to guanine occurred predominantly on the level of nucleoside di- or triphosphates. Strain MB-1517 incorporated adenine-8-(14)C into nucleic acids extremely poorly. This correlated with results obtained with cell-free extracts; strain MB-1517 showed much less adenosine monophosphate (AMP) pyrophosphorylase activity than did MB-1356. Likewise, guanineless MB-1517 converted diaminopurine to its nucleotide much more slowly than did the nonexacting purine auxotroph. The results indicated that the lack of growth of nonexacting auxotrophs on diaminopurine alone is due not to an inability to convert the analogue to nucleic acid adenine but to the greater capacity of the nonexacting auxotrophs to convert diaminopurine to its 5'-ribonucleotide. Presumably, this compound, or a coenzyme analogue produced from it, inhibits growth of mutants which cannot make AMP de novo and only when the medium is devoid of adenine.

Adenine↗
PubMed1967

Phosphohydrolases of a Bacillus subtilis mutant accumulating inosine and hypoxanthine.

Although adenine-requiring auxotrophs of Bacillus subtilis accumulate large quantities of inosine or hypoxanthine, or of both, they do not accumulate inosine-5'-monophosphate (IMP). Experiments directed at understanding this phenomenon were conducted with an adenineless auxotroph and with a mutant derived from it which lacked alkaline phosphohydrolase. It was found that B. subtilis contains four different phosphohydrolases. Only one is an extracellular enzyme; it is a 5'-nucleotide phosphohydrolase which can be inhibited by addition of CuSO(4) to the medium. Of the three cellular enzymes, only one, an acid phosphohydrolase, cannot attack 5'-nucleotides; this enzyme is not repressed by inorganic phosphate. One of the two remaining surface-bound enzymes is a nonspecific alkaline phosphohydrolase which attacks both 5'-nucleotides and p-nitrophenyl phosphate; this is the only phosphohydrolase that is markedly repressed by inorganic phosphate. The other surface-bound enzyme is a nonrepressible 5'-nucleotide phosphohydrolase with double pH optima: one at neutrality and the other near pH 9.0. The experiments indicate that the absence of IMP in the extracellular broth is due to degradation of internally accumulated IMP to inosine by the cellular 5'-nucleotide phosphohydrolase.

Bacillus subtilis↗
PubMed1967

Thiamine-dependent accumulation of tetramethylpyrazine accompanying a mutation in the isoleucine-valine pathway.

A mutant of Corynebacterium glutamicum was found to accumulate high concentrations of a material which crystallized upon cooling of the broth. The compound was identified as tetramethylpyrazine. The mutant was found to require isoleucine, valine, leucine, and pantothenate for growth. All four requirements probably result from the loss of a single enzyme of the isoleucine-valine pathway. Since similar mutants of Neurospora crassa accumulate acetoin, the present mutant probably forms tetramethylpyrazine from acetoin. Accumulation of tetramethylpyrazine was dependent upon addition of thiamine. This observation is consistent with the known activity of diphosphothiamine as a cofactor for the formation of acetolactate (a precursor of acetoin) from pyruvate.

Corynebacterium↗