Journal article

Publication year: 1993

Pages: 341-349

Journal: European Journal of Biochemistry

Volume number: 215

Issue number: 2

ISSN: 0014-2956

DOI Link: https://doi.org/10.1111/j.1432-1033.1993.tb18040.x

Publisher: Wiley: No OnlineOpen

Abstract: 

L-Serine dehydratase from the Gram-positive bacterium Peptostreptococcus asaccharolyticus is novel in the group of enzymes deaminating 2-hydroxyamino acids in that it is an iron-sulfur protein and lacks pyridoxal phosphate [Grabowski, R. and Buckel, W. (1991) Eur. J. Biochem. 199, 89-94]. It was proposed that this type Of L-serine dehydratase is widespread among bacteria but has escaped intensive characterization due to its oxygen lability. Here, we present evidence that another Gram-positive bacterium, Clostridium propionicum, contains both an iron-sulfur-dependent L-serine dehydratase and a pyridoxal-phosphate-dependent L-threonine dehydratase. These findings support the notion that two independent mechanisms exist for the deamination of 2-hydroxyamino acids.

L-Threonine dehydratase was purified 400-fold to apparent homogeneity and revealed as being a tetramer of identical subunits (m = 39 kDa). The purified enzyme exhibited a specific activity of 5 mukat/mg protein and a K(m) for L-threonine of 7.7 mM. L-Serine (K(m) = 380 mM) was also deaminated, the V/K(m) ratio, however, being 118-fold lower than the one for L-threonine. L-Threonine dehydratase was inactivated by borohydride, hydroxylamine and phenylhydrazine, all known inactivators of pyridoxal-phosphate-containing enzymes. Incubation with (NaBH4)-H-3 specifically labelled the enzyme. Activity of the phenylhydrazine-inactivated enzyme could be restored by pyridoxal phosphate.

L-Serine dehydratase was also purified 400-fold, but its extreme instability did not permit purification to homogeneity. The enzyme was specific for L-serine (K(m) = 5 mM) and was inhibited by L-cysteine (K(i) = 0.5 mM) and D-serine (K(i) = 8 mM). Activity was insensitive towards borohydride, hydroxylamine and phenylhydrazine but was rapidly lost upon exposure to air. Fe2+ specifically reactivated the enzyme. L-Serine dehydratase was composed of two different subunits (alpha, m = 30 kDa; beta, m = 26 kDa), their apparent molecular masses being similar to the ones of the two subunits of the iron-sulfur-dependent enzyme from P asaccharolyticus. Moreover, the N-terminal sequences of the small subunits from these two organisms were found to be 47% identical. In addition, 38% identity with the N-terminus of one of the two L-serine dehydratases of Escherichia coli was detected.

Harvard Citation style: HOFMEISTER, A., GRABOWSKI, R., LINDER, D. and BUCKEL, W. (1993) L-SERINE AND L-THREONINE DEHYDRATASE FROM CLOSTRIDIUM-PROPIONICUM - 2 ENZYMES WITH DIFFERENT PROSTHETIC GROUPS, European Journal of Biochemistry, 215(2), pp. 341-349. https://doi.org/10.1111/j.1432-1033.1993.tb18040.x

APA Citation style: HOFMEISTER, A., GRABOWSKI, R., LINDER, D., & BUCKEL, W. (1993). L-SERINE AND L-THREONINE DEHYDRATASE FROM CLOSTRIDIUM-PROPIONICUM - 2 ENZYMES WITH DIFFERENT PROSTHETIC GROUPS. European Journal of Biochemistry. 215(2), 341-349. https://doi.org/10.1111/j.1432-1033.1993.tb18040.x