<p>This entry represents LpxH, or UDP-2,3-diacylglucosamine hydrolase (or pyrophosphatase), which is an essential enzyme in <taxon tax_id="562">Escherichia coli</taxon> that catalyses the fourth step in lipid A biosynthesis. This reaction involves pyrophosphate bond hydrolysis of the precursor UDP-2,3-diacylglucosamine to yield 2,3-diacylglucosamine 1-phosphate and UMP [<cite idref="PUB00014937"/>]. Several Gram-negative bacteria have homologues of LpxH and/or LpxH2, while others have only distant orthologues of LpxH or LpxH2, or lack these enzymes altogether [<cite idref="PUB00013505"/>].</p>