Plays a role in xanthan depolymerization pathway by cleaving the linkage between the terminal mannosyl and glucuronyl residues of the side chain of xanthan to liberate pyruvylated mannose. Is highly specific for pyruvylated side-chains of xanthan and is not effective with hyaluronate, chondroitin A, gellan, heparin or pectin. Eliminative cleavage of the terminal beta-D-mannosyl-(1->4)-beta-D-glucuronosyl linkage of the side-chain of the polysaccharide xanthan, leaving a 4-deoxy-alpha-L-threo-hex-4-enuronosyl group at the terminus of the side-chain. Activated by Co(2+) at 1 mM. Completely inhibited by Hg(2+) but not affected by other divalent cations. Intensely inhibited by NaCl and KCl at 150 mM, in particular by the Na(+) and K(+) ions but not the Cl(-) ions. Partially inhibited by iodoacetamide and N-ethylmaleimide at 1 mM but not by dithiothreitol, reduced glutathione or 2-mercaptoethanol. kcat is 2170 sec(-1). Optimum pH is 5.5 (in the presence of sodium acetate). Active between pH 6.5 and 9. Optimum temperature is 50 degrees Celsius. Stable at 4 degrees Celsius at pH 6.5 - 9. 60% loss of activity when incubated at 45 degrees Celsius and pH 7.0 for 10 minutes. Monomer. The 99 kDa precursor is converted to a mature form (77 kDa) through the removal of a C-terminal (22 kDa) fragment without any loss in activity. Belongs to the polysaccharide lyase 8 family.