Abstract
The catabolism of fungal 4-aminobutyrate (GABA) occurs via succinic semialdehyde (SSA). Succinic semialdehyde dehydrogenase (SSADH) from the acidogenic fungus Aspergillus niger was purified from GABA grown mycelia to the highest specific activity of 277 nmol min(-1) mg(-1), using phenyl Sepharose and DEAE Sephacel chromatography. The purified enzyme was specific for its substrates SSA and NAD+. The substrate inhibition observed with SSA was uncompetitive with respect to NAD+. While product inhibition by succinate was not observed, NADH inhibited the enzyme competitively with respect to NAD+ and noncompetitively with respect to SSA. Dead-end inhibition by AMP and p-hydroxybenzaldehyde (pHB) was analyzed. The pHB inhibition was competitive with SSA and uncompetitive with NAD+; AMP competed with NAD+. Consistent with the kinetic data, a sequential, ordered Bi Bi mechanism is proposed for this enzyme.
Publication types
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Research Support, Non-U.S. Gov't
MeSH terms
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Adenosine Monophosphate / metabolism
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Adenosine Monophosphate / pharmacology
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Aspergillus niger / enzymology*
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Aspergillus niger / metabolism
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Benzaldehydes / metabolism
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Benzaldehydes / pharmacology
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Binding, Competitive
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Biocatalysis / drug effects
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Fungal Proteins / isolation & purification
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Fungal Proteins / metabolism*
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Kinetics
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Mycelium / enzymology
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Mycelium / metabolism
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NAD / metabolism
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NAD / pharmacology
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Protein Binding
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Substrate Specificity
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Succinate-Semialdehyde Dehydrogenase / isolation & purification
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Succinate-Semialdehyde Dehydrogenase / metabolism*
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gamma-Aminobutyric Acid / analogs & derivatives*
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gamma-Aminobutyric Acid / metabolism
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gamma-Aminobutyric Acid / pharmacology
Substances
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Benzaldehydes
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Fungal Proteins
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NAD
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Adenosine Monophosphate
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gamma-Aminobutyric Acid
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Succinate-Semialdehyde Dehydrogenase
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succinic semialdehyde
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4-hydroxybenzaldehyde