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Microbiology 141 (1995), 1139-1145
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microbiology, Vol 141, 1139-1145, Copyright © 1995 by Society for General Microbiology

ARTICLES

The tylosin producer, Streptomyces fradiae, contains a second valine dehydrogenase

LT Nguyen, KT Nguyen, J Spizek and V Behal
Institute of Microbiology, Academy of Sciences of Czech Republic, Prague.

A second NAD-dependent valine dehydrogenase (VDH) of Streptomyces fradiae was detected and purified to homogeneity by affinity chromatography on Reactive-Blue 2 Sepharose followed by gel filtration and Mono Q fast protein liquid chromatography. The relative molecular masses of the native enzyme and its subunits were determined to be 80,000 and 41,000, respectively, indicating that the enzyme is a homodimer. The enzyme was the only active VDH in S. fradiae; its activity was significantly induced by L-valine, but was repressed by ammonia. Among branched- and straight-chain amino acids that serve as enzyme substrates, L-2-aminobutyrate and L-valine are preferred. Significant activities were found with deamino-NAD+ and 3- pyridinealdehyde-NAD+. The molecular and catalytic properties of the enzyme distinguish it from the enzyme previously purified, and thus indirectly indicate the existence of two VDHs in S. fradiae.




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