Isoelectric focusing of native urinary uromodulin (Tamm-Horsfall protein) shows no physicochemical differences between stone formers and non-stone formers

Recent studies have suggested the occurrence of an abnormal form of uromodu lin in stone formers which may be related to a reduced sialic acid content of the protein in these patients. Previous attempts to demonstrate these di fferences have required extensive sample processing prior to analysis, whic h may in itself alter the nature and behaviour of uromodulin. By employing a sensitive detection system of enhanced chemiluminescence on Western blots following isoelectric focusing we have been able to study the physicochemi cal properties of uromodulin in whole unprocessed urine from 50 idiopathic calcium stone formers and 15 non-stone formers. Uromodulin. desialated in v itro with either acid or neuraminidase was also analysed using the same sys tem. All urine samples analysed from stone formers and non-stone formers sh owed a single band of pi 3.5 after isoelectric focusing. Desialated uromodu lin showed a series of bands ranging from pI 4.0 to 5.1 reflecting differen t amounts of sialic acid removed. We conclude there are no charge-related d ifferences in native uromodulin between stone formers and non-stone formers , in particular none relating to the sialic acid content of the protein.