Prochlorococcus marinus strain PCC 9511, a picoplanktonic cyanobacterium, synthesizes the smallest urease

The urease from the picoplanktonic oceanic Prochlorococcus marinus sp. stra in PCC 9511 was purified 900-fold to a specific activity of 94.6 mu mol ure a min(-1) (mg protein)(-1) by heat treatment and liquid chromatography meth ods. The enzyme, with a molecular mass of 168 kDa as determined by gel filt ration, is the smallest urease known to date. Three different subunits with apparent molecular masses of 11 kDa (gamma or UreA; predicted molecular ma ss 11 kDa), 13 kDa (beta or UreB; predicted molecular mass 12 kDa) and 63 k Da (alpha or UreC; predicted molecular mass 62 kDa) were detected in the na tive enzyme, suggesting a quaternary structure of (alpha beta gamma)(2). Th e K-m of the purified enzyme was determined as being 0.23 mM urea. The urea se activity was inhibited by HgCl2, acetohydroxamic acid and EDTA but neith er by boric acid nor by L-methionine-DL-sulfoximine. Degenerate primers wer e designed to amplify a conserved region of the ureC gene. The amplificatio n product was then used as a probe to clone a 5.7 kbp fragment of the P. ma rinus sp. strain PCC 9511 genome. The nucleotide sequence of this DNA fragm ent revealed two divergently orientated gene clusters, ureDABC and ureEFG, encoding the urease subunits, UreA, UreB and UreC, and the urease accessory molecules UreD, UreE, UreF and UreC. A putative NtcA-binding site was foun d upstream from ureEFC, indicating that this gene cluster might be under ni trogen control.