The Reactive Site of Human Inter-α-Trypsin Inhibitor is in the Amino-Terminal Half of the Protein

Abstract

Human inter-alpha-trypsin inhibitor has been found to inactivate human trypsin, chymotrypsin, neutrophil elastase and cathepsin G. The protein was cleaved into two major fragments without loss of activity by incubation with Serratia marcescens metalloproteinase, and these were separated by ion-exchange chromatography. Inhibitory activity was found in only one of the fragments, the amino-terminal sequence of which was found to be identical with that of the native protein, as well as with that reported earlier for the urinary trypsin inhibitor. It may thus be concluded that the reactive site of the inter-alpha-trypsin inhibitor is located in the amino-terminal region.

Inter‐α‐inhibitor in urine and calcium oxalate urinary crystals

“…This probably results more from a historical preoccupation with the bikunin portion of the protein and a consequent lack of interest in H1 and H2, rather than failed attempts to detect them. Previously, the isolation or detection of proteins related to IαI in urine involved either highly specific procedures [ 11–13, 15], which would not have allowed the isolation of the heavy chains, or the measurement of urinary antitrypsin activity [ 23], which is confined to the bikunin moiety of the molecule [ 24]. Furthermore, bikunin itself is known to be active against several proteases [ 25] and is the only portion of IαI both to have been isolated from urine, and shown to inhibit CaOx crystallization [ 11–15, 17].…”

The Uniform Galactose 4‐Sulfate Structure in the Carbohydrate‐Protein Linkage Region of Human Urinary Trypsin Inhibitor

“…The HOD signal was suppressed by presaturation during 4 s and 2 s for one-dimensional and two-dimensional (1D and 2D) spectra, respectively. To obtain 2D spectra, 512 experiments resulting in 2048 data points for a spectral width of 5000Hz were measured, and the time domain data were multiplied with a sine-bell for correlation spectroscopy (COSY; Aue et al, 1976;Nagayama et al, 1980).…”

“…Intraarticular injection of UTI improves the symptoms and clinical signs of rheumatoid arthritis markedly, which is ascribed to the inhibition of a plasminogen activator of the urokinase type (Kikuchi et al, 1987). The inhibitory activity of UTI i s attributable to the protein moiety (Gebhard et al, 1989), which consists of 143 amino acids (Wachter and Hochstrasser, 1981) identical in amino acid sequence to that of the L chain, bikunin, of inter-a-trypsin inhibitor (ITI) (Morii andTravis, 1985: Reisinger et al, 1985). IT1 is considered to be a metabolic precursor of UTI (Hochstrasser et al., : Balduyck et al, 1989 and bears an undersulfated chondroitin 4-sulfate chain attached to SerlO of the L chain.…”

Inter-α-inhibitor in calcium stones

“…Bikunin, with which the anti-tryptic activity of IαI is associated [34], is well known to be present in urine [8], as are its fragments HI14 and HI8 [5]. Using an antibody which specifically reacts with bikunin, a 35-kDa form of the peptide has been shown to be present in trace amounts in CaOx crystals precipitated from human and rat urine [16] ; a form with a molecular mass of approx.…”