1.A broad spectrum of proteins has been detected within calcium stones. A newcomer to the field of urolithiasis is the blood protein inter-α-inhibitor. Inter-α-inhibitor comprises three protein chains linked by chondroitin sulphate: two heavy chains, H1 (65 ;kDa) and H2 (70 ;kDa) and a light chain (approx. 30 ;kDa) most commonly known as bikunin. The physiological function of the two heavy chains is unknown; nor has their presence been reported in urine. However, bikunin has been implicated in various renal diseases, including urolithiasis.
2.This study was undertaken to determine which chains of inter-α-inhibitor are actually present in calcium kidney stones. Organic extracts were obtained from 10 calcium stones and analysed by SDS/PAGE and Western blotting. The H1 and H2 chains of inter-α-inhibitor were detected in 9 of the 10 stones, but only one stone contained a protein with a molecular mass close to that of bikunin (30–35 ;kDa).
3.These results demonstrate for the first time that H1 and H2 are present in stones and show that the bikunin chain of inter-α-inhibitor may not be the only part of the molecule implicated in stone formation.