초록
<P><B>Background</B></P><P>In white biotechnology biocatalysis represents a key technology for chemical functionalization of non-natural compounds. The plasmid-born overproduction of an alcohol dehydrogenase, an L-alanine-dependent transaminase and an alanine dehydrogenase allows for redox self-sufficient amination of alcohols in whole cell biotransformation. Here, conditions to optimize the whole cell biocatalyst presented in (Bioorg Med Chem 22:5578–5585, 2014), and the role of L-alanine for efficient amine functionalization of 1,10-decanediol to 1,10-diaminodecane were analyzed.</P><P><B>Results</B></P><P>The enzymes of the cascade for amine functionalization of alcohols were characterized <I>in vitro</I> to find optimal conditions for an efficient process. Transaminase from <I>Chromobacterium violaceum</I>, Ta<SUB>Cv</SUB>, showed three-fold higher catalytic efficiency than transaminase from <I>Vibrio fluvialis</I>, Ta<SUB>Vf</SUB>, and improved production at 37°C. At 42°C, Ta<SUB>Cv</SUB> was more active, which matched thermostable alcohol dehydrogenase and alanine dehydrogenase and improved the 1,10-diaminodecane production rate four-fold. To study the role of L-alanine in the whole cell biotransformation, the L-alanine concentration was varied and 1,10.diaminodecane formation tested with constant 10 mM 1,10- decanediol and 100 mM NH<SUB>4</SUB>Cl. Only 5.6% diamine product were observed without added L-alanine. L-alanine concentrations equimolar to that of the alcohol enabled for 94% product formation but higher L-alanine concentrations allowed for 100% product formation. L-alanine was consumed by the <I>E. coli</I> biocatalyst, presumably due to pyruvate catabolism since up to 16 mM acetate accumulated. Biotransformation employing <I>E. coli</I> strain YYC202/pTrc99a-<I>ald</I>-<I>adh</I>-<I>ta</I><SUB>Cv</SUB>, which is unable to catabolize pyruvate, resulted in conversion with a selectivity of 42 mol-%. Biotransformation with <I>E. coli</I> strains only lacking pyruvate oxidase PoxB showed similar reduced amination of 1,10-decanediol indicating that oxidative decarboxylation of pyruvate to acetate by PoxB is primarily responsible for pyruvate catabolism during redox self-sufficient amination of alcohols using this whole cell biocatalyst.</P><P><B>Conclusion</B></P><P>The replacement of the transaminase Ta<SUB>Vf</SUB> by Ta<SUB>Cv</SUB>, which showed higher activity at 42°C, in the artificial operon <I>ald-adh</I>-<I>ta</I> improved amination of alcohols in whole cell biotransformation. The addition of L-alanine, which was consumed by <I>E. coli</I> via pyruvate catabolism, was required for 100% product formation possibly by providing maintenance energy. Metabolic engineering revealed that pyruvate catabolism occurred primarily via oxidative decarboxylation to acetate by PoxB under the chosen biotranformation conditions.</P><P><B>Electronic supplementary material</B></P><P>The online version of this article (doi:10.1186/s12934-014-0189-x) contains supplementary material, which is available to authorized users.</P>