Complete amino acid sequence of jack bean urease

The subunit structure of jack bean urease has been unresolved in spite of many investigations. Thus far, the molecular weight for the native urease seem to range from 480,000 to 590,000 and the values for the monomer range from 30,000 to 97,000. The complete amino acid sequence of jack bean urease has been determined primarily by sequencing cyanogen bromide peptides, which were aligned by overlapping peptides obtained by lysylendopeptidase digestion of the protein and tryptic digestion of the citraconylated protein. The protein contains 840 amino acid residues in a single polypeptide chain and the subunit molecular weight calculated from the sequence is 90,790. The value of 544,740 for the hexamer, consistent with the value of 580,000 determined for intact urease by centrifugal analyses, indicated that urease consists of six subunits. Thirteen of 25 histidine residues in the urease subunit are crowded in the region between residues 479 and 607. Urease is a nickel metalloenzyme and the nickel has an essential role in catalysis by this enzyme. It is noteworthy that cysteine-592, which is recognized as essential for enzymatic activity and is related to the nickel ion in the active center, is located on this histidine-rich sequence.This article was presented during the proceedings of the International Conference on Macromolecular Structure and Function, held at the National Defence Medical College, Tokorozawa, Japan, December 1985.