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R L Starkey

Publications and source records attributed to R L Starkey.

17 recordsLinked to original sources
PubMed1970

Dissimilation of Methionine by Achromobacter starkeyi.

Methionine was decomposed by some bacteria which were isolated from soil. The sulfur of the methionine was liberated as methanethiol, and part of this became oxidized to dimethyl disulfide. Detailed studies with one of these cultures, Achromobacter starkeyi, indicated that the first step in methionine decomposition was its oxidadative deamination to alpha-keto-gamma-methyl mercaptobutyrate by a constitutive amino acid oxidase. The following steps were carried out by inducible enzymes, the synthesis of which was inhibited by chloramphenicol. alpha-Keto-gamma-methyl mercaptobutyrate was split producing methanethiol and alpha-keto butyrate which was oxidized to propionate. The metabolism of propionate was similar to that described for animal tissues; the propionate was carboxylated to succinate via methyl malonyl coenzyme A, and the succinate was metabolized through the Krebs cycle.

Journal Article↗
PubMed1969

Microbial decomposition of methionine and identity of the resulting sulfur products.

Various bacteria, actinomycetes, and filamentous fungi decomposed methionine, but only certain aerobic bacteria isolated from soil decomposed it in the absence of other organic substrates. These bacteria could grow on methionine as the only organic substrate and source of nitrogen and sulfur. Methionine was first deaminated and then demethiolated with production of methanethiol, part of which was oxidized to dimethyl disulfide. The amount of methanethiol that was oxidized varied with different cultures. A bacterial culture initially unable to grow on methionine developed capacity to do this in a medium which contained methionine and other growth substrates. The two sulfur products, methanethiol and dimethyl disulfide, are volatile and escaped from the media, resulting in a decrease in the sulfur content proportional to the amount of methionine decomposed.

Bacteria↗
PubMed1969

Dissimilation of methionine by fungi.

Soil fungi that attacked methionine required a utilizable source of energy such as glucose for growth. This is an example of co-dissimilation. Experiments with one of the fungi, representative of the group, are reported. In the absence of glucose, pregrown mycelium, even when depleted of energy reserves, oxidatively deaminated methionine with accumulation of alpha-keto-gamma-methyl mercapto butyric acid and alpha-hydroxy-gamma-methyl mercapto butyric acid. When glucose was provided, all of the sulfur of methionine was released as methanethiol, part of which was oxidized to dimethyl disulfide. No sulfate, sulfide, or hydrosulfide products were detected. Evidence was obtained that deaminase and demethiolase were constitutive. Deamination preceded demethiolation and alpha-keto butyric acid accumulated as a product of the two reactions. Other carbon residues were alpha-hydroxy butyric acid and alpha-amino butyric acid. Inability of the fungus to metabolize alpha-keto butyrate was responsible for its inability to utilize methionine as a source of carbon and energy. Several other fungi isolated from soil grew on alpha-amino butyrate but could not grow on methionine owing to inability to demethiolate it.

Arabinose↗
PubMed1969

Dissimilation of methionine by a demethiolase of Aspergillus species.

Enzyme preparations obtained from the mycelium of Aspergillus species broke down methionine by co-dissimilation. The deaminase and demethiolase activities of crude extracts were increased 100-fold by precipitation with (NH(4))(2)SO(4) and column chromatography on diethylaminoethyl cellulose. The enzyme acted on d-methionine but not on l-methionine. The enzyme was labile: it was inactivated by oxygen and ascorbic acid but ethylenediaminetetraacetic acid and mercaptoethanol preserved its activity. Enzyme activity decreased even at 4 and -30 C and was lost rapidly above 45 C. It was most rapid at 35 C and at pH 8.0 to 9.0. For the following reasons, it was concluded that deamination and demethiolation of methionine were effected by the same enzyme: both activities increased equally at each stage of purification; ammonia, methanethiol, and alpha-keto butyric acid were formed in amounts equivalent to the amount of methionine dissimilated; the K(m) and optimal pH for formation of both keto acid and methanethiol were the same; both activities remained in the same fractions that were separated by electrophoresis and the activities were equivalent. The purified enzyme demethiolated alpha-keto methionine and alpha-hydroxy methionine and split the sulfur linkage of ethionine but did not cleave cystathionine. Few amino acids were deaminated. The enzyme was sensitive to some carbonyl and sulfhydryl reagents and was relatively insensitive to heavy metals other than Hg(++). The K(m) was 1.3 x 10(-3) to 1.5 x 10(-3)m at pH 7.0. No requirement for cofactors was noted, and attempts to dissociate the enzyme, including dialysis with hydroxylamine, were unsuccessful.

Aspergillus↗