Effects of anoxic conditions on the enzymatic conversion of D,L-2-amino-thiazoline-4-carboxylic acid to L-cystine
✍ Scribed by K. H. Nam; O. H. Ryu; J. Park; C. S. Shin
- Publisher
- John Wiley and Sons
- Year
- 1997
- Tongue
- English
- Weight
- 444 KB
- Volume
- 17
- Category
- Article
- ISSN
- 0138-4988
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✦ Synopsis
The effects of anoxic conditions on product inhibition and the stability of L-ATC hydrolase were investigated in the conversion of D,L-2-amino-A2-thiamline-4-carboxylic acid (D, L-ATC ) to L-cystine using the cell free extract enzyme of Pseudomonas sp. in the presence of hydroxylamine. At L-cysteine equivalent levels, where one mole of L-systine was counted as two moles of L-cysteine, L-cystine inhibited the L-ATC hydrolase reaction to a greater extent than Lcysteine. In air. the product occurred predominantly as L-cystine (94.9%), whereas in a nitrogen atmosphere the product occurred as a mixture of L-cysteine (39.3%) and L-cystine (40.7%). As a result, less product inhibition took place in nitrogen. The activity of L-ATC hydrolase was almost fully lost after 20 h of incubation by shaking at 30 "C in air, but considerable activity remained under the anoxic conditions of nitrogen. A kinetic analysis of the reactions confirmed that reduced product inhibition and enhanced enzyme stability in nitrogen result in a more efficient enzyme reaction. The inactivation rate constant (kl) was estimated to be 0.1 1 h -1 in nitrogen and 0.22 -1 in air, indicating that the stability of L-ATC hydrolase in nitrogen was greater than in air. The values of the Kp and KPZ constants related to product inhibition were 43.36 mM and 30.48 mM for L-cysteine and 2-cystine, respectively, where higher values were an indication of less product inhibition. The value of the rate constant (kz) for the oxidation of L-cysteine to L-cystine was 0.09 hin nitrogen and 1.01 h -in air, suggesting that the oxidation of L-cysteine to L-cystine proceeds faster in air than in nitrogen.