▁t et ram ers ▁and ▁bind ▁one ▁metal ▁atom ▁per ▁α β ▁unit . ▁The ▁ 3 - D ▁structures ▁of ▁a ▁number ▁of ▁N H ases ▁have ▁been ▁determined . ▁The ▁α ▁sub unit ▁consists ▁of ▁a ▁long ▁extended ▁N - term inal ▁" arm ", ▁containing ▁two ▁α - hel ices , ▁and ▁a ▁C - term inal ▁domain ▁with ▁an ▁unusual ▁four - layer ed ▁structure ▁( α - β - β - α ). ▁The ▁ β ▁sub unit ▁consists ▁of ▁a ▁long ▁N - term inal ▁loop ▁that ▁wra ps ▁around ▁the ▁α ▁sub unit , ▁a ▁hel ical ▁domain ▁that ▁pack s ▁with ▁N - term inal ▁domain ▁of ▁the ▁α ▁sub unit , ▁and ▁a ▁C - term inal ▁domain ▁consisting ▁of ▁a ▁ β - roll ▁and ▁one ▁short ▁hel ix . ▁ ▁Assembly ▁ ▁An ▁assembly ▁path way ▁for ▁nit rile ▁hyd rat ase ▁was ▁first ▁proposed ▁when ▁gel ▁fil tr ation ▁experiments ▁found ▁that ▁the ▁complex ▁exists ▁in ▁both ▁α β ▁and ▁α 2 β 2 ▁forms . ▁In ▁vit ro ▁experiments ▁using ▁mass ▁spect rom etry ▁further ▁revealed ▁that ▁the ▁α ▁and ▁ β ▁sub un its ▁first ▁assemble ▁to ▁form ▁the ▁α β ▁dim er . ▁The ▁dim ers ▁can ▁then ▁subsequently ▁interact ▁to ▁form ▁a ▁t et ram er . ▁ ▁Mechan ism ▁The ▁metal ▁centre ▁is ▁located ▁in ▁the ▁central ▁cav ity ▁at ▁the ▁interface ▁between ▁two ▁sub un its . ▁All ▁protein ▁lig ands ▁to ▁the ▁metal ▁atom