1. α1-Proteinase inhibitor (α1-antitrypsin) was excreted in the faeces of patients with inflammatory bowel disease in different molecular forms: Mr-51 000 and Mr-45 000 forms were widely found in the stools of patients with active disease, whereas a Mr-38 000 species was frequently recovered from healthy subjects and patients with quiescent disease (Mizon, Becuwe, Balduyck et al. Clin. Chem. 1988; 34, 2268–70).
2. N-Terminal sequencing of the Mr-38000 form of α1-proteinase inhibitor, after SDS/PAGE and electro-transfer on polyvinyl difluoride membranes, showed that it differed from plasma α1-proteinase inhibitor by the loss of 17 N-terminal amino acids.
3. Carbohydrate analysis of the isolated Mr-38 000 form revealed a total lack of neutral sugars.
4. In contrast, the Mr-51000 form of α1-proteinase inhibitor is glycosylated and thus could be differentiated by virtue of its reactivity with concanavalin A. The analysis of 25 faecal extracts from patients with Crohn's disease allowed us to confirm that the presence of the glycosylated form of α1-proteinase inhibitor was closely related to the degree of inflammation.
5. From these data, it may be hypothesized that the hydrolytic activity of some glycosidases is greatly reduced in active Crohn's disease.