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671.
The anaerobic metabolism of phenylalanine was studied in the denitrifying bacterium Thauera aromatica, a member of the β-subclass of the Proteobacteria. Phenylalanine was completely oxidized and served as the sole source of
cell carbon. Evidence is presented that degradation proceeds via benzoyl-CoA as the central aromatic intermediate; the aromatic
ring-reducing enzyme benzoyl-CoA reductase was present in cells grown on phenylalanine. Intermediates in phenylalanine oxidation
to benzoyl-CoA were phenylpyruvate, phenylacetaldehyde, phenylacetate, phenylacetyl-CoA, and phenylglyoxylate. The required
enzymes were detected in extracts of cells grown with phenylalanine and nitrate. Oxidation of phenylalanine to benzoyl-CoA
was catalyzed by phenylalanine transaminase, phenylpyruvate decarboxylase, phenylacetaldehyde dehydrogenase (NAD+), phenylacetate-CoA ligase (AMP-forming), enzyme(s) oxidizing phenylacetyl-CoA to phenylglyoxylate with nitrate, and phenylglyoxylate:acceptor
oxidoreductase. The capacity for phenylalanine oxidation to phenylacetate was induced during growth with phenylalanine. Evidence
is provided that α-oxidation of phenylacetyl-CoA is catalyzed by a membrane-bound enzyme. This is the first report on the
complete anaerobic degradation of an aromatic amino acid and the regulation of this process.
Received: 6 March 1997 / Accepted: 16 May 1997 相似文献
672.
[3H]MK-801 binding was used as an index of the glutamate receptor N-methyl-D-aspartate-subtype channel to examine the influence of gender, age, mode of death (agonal status), interval between death and autopsy (postmortem delay), and time in storage at -70 degrees C in well washed homogenate preparations from postmortem human frontal cortex. Basal binding and the modulatory effects of glutamate, glycine, spermidine, and zinc were examined with respect to these variables. Basal binding was sensitive to agonal status, being higher in sudden death cases. The effect of added glutamate and glycine was sensitive to age, with a trend toward lower binding with increasing age. The effect of added spermidine alone was sensitive to storage time at -70 degrees C, the binding being higher with longer storage time. The effect of added zinc was also sensitive to postmortem delay, with zinc causing a greater reduction in binding with shorter postmortem delays. Thus, with the exception of gender, all variables examined influenced [3H]MK-801 binding, highlighting the attention that should be given to these factors in postmortem studies in normal and diseased human subjects. 相似文献