Growth response to 4-hydroxy-l-threonine of Escherichia coli mutants blocked in vitamin B6 biosynthesis

AbstractMutants of Escherichia coli (pdx B and pdx C) which are blocked in the biosynthesis of pyridoxol (vitamin B6) showed a growth response to 4-hydroxy-l-threonine. This observation constitutes the first direct evidence in support of the view that 4-hydroxy-l-threonine is implicated in the biosynthesis of vitamin B6. 1-Aminopropan-2,3-diol, the decarboxylation product of 4-hydroxy-l-threonine, does not support the growth of these mutants. Deuterium from deuterium-labelled 1-aminopropan-2,3-diol was not incorporated into pyridoxol

Formation of the Ureido Bond in Anabaenopeptins by ApnA from Planktothrix agardhii CYA 126/8.

The process leading to the formation of the ureido bond linking lysine and tyrosine/arginine, respectively, in the anabaenopeptins has been reconstituted in vitro. Trapping experiments suggest that an enzyme bound lysine -carbamic acid is an intermediate. Labeling experiments with 18O-bicarbonate suggest that a carbamic acid mixed anhydride is formed from the tyrosine/arginine thioester and subsequently rearranged to yield the ureido-dipeptide

Isolation and Structure Determination of Two Microcystins and Sequence Comparison of the McyABC Adenylation Domains in <i>Planktothrix</i> Species

Microcystins (MCs) are toxic heptapeptides found in cyanobacteria and share the common structure <i>cyclo</i>(-d-Ala¹-l-X²-d-isoMeAsp³-l-Z⁴-Adda⁵-d-isoGlu⁶-Mdha⁷). The letters X and Z in the general formula above represent a wide range of l-amino acids that occupy positions 2 and 4, respectively. In general the variation in structural variants is due to the exchange of amino acids in position 7, 2, and 4. In the present work we report two homotyrosine (Hty)-containing microcystin variants, [d-Asp³,(<i>E</i>)-Dhb⁷]-MC-HtyY (<b>1</b>) and [d-Asp³,(<i>E</i>)-Dhb⁷]-MC-HtyHty (<b>2</b>), which were isolated from strain No80 of <i>Planktothrix rubescens.</i> Their structures were elucidated using amino acid analysis as well as 1D and 2D NMR techniques. The adenylation domains of McyABC involved in amino acid activation in positions 7, 2, and 4 of the microcystin molecule, respectively, were compared with corresponding genes of <i>Planktothrix</i> strain CYA126/8 producing [d-Asp³,Mdha⁷]-MC-RR and [d-Asp³,Mdha⁷]-MC-LR. While the adenylation domain comparison of McyAB between the two <i>Planktothrix</i> strains revealed considerable DNA recombination, the adenylation domain of McyC showed only a single amino acid substitution, which was correlated with the replacement of Arg by Hty in position 4 of the microcystin molecule