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Abstract : |
Extracts of nitrate-grown mats of some filamentous fungi namely, Aspergillus terreus DSM 826, Aspergillus niger NRRL3, Aspergillus terricola strain and Penicillium politans NRC-510 could deaminate each of L-serine and L-threonine leading to formation of equimolar amounts of the corresponding α-keto acid and ammonia. Aspergillus terreus extracts showed somewhat higher activity. This activity did not increase when the organism was grown on medium containing L-serine, instead of nitrate, as nitrogen source. The deaminating activities of Aspergillus terreus extracts with L-serine and L-threonine responded similarly to changes in the conditions of the reactions. Both activities were optimum, with almost the same profile, at pH 8 of 0.04-0.06 M Tris-HCl buffer and 50°C. Exposure of the extracts to 50°C or above, in absence of the substrate, revealed almost similar degrees of inactivation with the two substrates. The activity in presence of the two substrates in the same reaction mixture was much less than additive. The substrate saturation kinetics with each of L-serine and L-threonine was hyperbolic and the apparent km values for L-serine and L-threonine was 2.7 x 10-4 and 5 x 10-4 M, respectively. On fractionation of extract proteins using DEAE Sephadex G A-25 column chromatography, the two activities were eluted in the same protein fractions, with the same activity peaks and with almost constant ratios. The ratio of activity with L-threonine to that with L-serine was about 0.6:1.0 in all experiments carried out., Extracts of nitrate-grown mats of some filamentous fungi namely, Aspergillus terreus DSM 826, Aspergillus niger NRRL3, Aspergillus terricola strain and Penicillium politans NRC-510 could deaminate each of L-serine and L-threonine leading to formation of equimolar amounts of the corresponding أƒإ½أ‚آ±-keto acid and ammonia. Aspergillus terreus extracts showed somewhat higher activity. This activity did not increase when the organism was grown on medium containing L-serine, instead of nitrate, as nitrogen source. The deaminating activities of Aspergillus terreus extracts with L-serine and L-threonine responded similarly to changes in the conditions of the reactions. Both activities were optimum, with almost the same profile, at pH 8 of 0.04-0.06 M Tris-HCl buffer and 50أƒâ€ڑأ‚آ°C. Exposure of the extracts to 50أƒâ€ڑأ‚آ°C or above, in absence of the substrate, revealed almost similar degrees of inactivation with the two substrates. The activity in presence of the two substrates in the same reaction mixture was much less than additive. The substrate saturation kinetics with each of L-serine and L-threonine was hyperbolic and the apparent km values for L-serine and L-threonine was 2.7 x 10-4 and 5 x 10-4 M, respectively. On fractionation of extract proteins using DEAE Sephadex G A-25 column chromatography, the two activities were eluted in the same protein fractions, with the same activity peaks and with almost constant ratios. The ratio of activity with L-threonine to that with L-serine was about 0.6:1.0 in all experiments carried out., |
