Mechanism for the hydrolysis of hyaluronan oligosaccharides by bovine testicular hyaluronidase.

Synthetic hyaluronan oligosaccharides with defined structures and their pyridylaminated derivatives were used to investigate the mechanism of hydrolysis of hyaluronan by bovine testicular hyaluronidase. The products of the hydrolysis were analyzed by HPLC and ion-spray mass spectroscopy (MS). It was confirmed that the minimum substrate for bovine testicular hyaluronidase is the hyaluronan hexasaccharide, even though it is a poor substrate that is barely cleaved, even on prolonged incubation. When hyaluronan octasaccharide was the substrate, increasing amounts of tetrasaccharide and hexasaccharide were produced with increasing time of incubation. Whereas disaccharide was not detectable in the reaction mixture by HPLC, MS analysis revealed trace amounts. The data suggest that the enzyme generates a disaccharide intermediate from hyaluronan oligosaccharide, the majority of which is transferred to the nonreducing ends of other oligosaccharides, only traces being released as free disaccharide. When hyaluronan octasaccharide, with an unsaturated glucuronic acid at the nonreducing end, was used as a substrate, only a tetrasaccharide was detected by HPLC. However, MS showed that the product was a mixture of equal amounts of two tetrasaccharides, one with and the other without the unsaturated glucuronic acid. This suggests that, in the case of substrates with a double bond at the nonreducing end, a tetrasaccharide is cleaved off instead of a disaccharide. The results of the experiments with pyridylaminated oligosaccharides were entirely consistent with these conclusions, and in addition showed the importance of the reducing end of the substrate for the enzyme to recognize the length of the saccharide.

Diversity in the degree of sulfation and chain length of the glycosaminoglycan moiety of urinary trypsin inhibitor isomers.

Five isomers with different electric charge were fractionated from human urinary trypsin inhibitor (UTI) by anion exchange HPLC. Intact low-sulfated chondroitin 4-sulfate chains from the isomers were analyzed by HPLC and mass spectrometry. Unsaturated disaccharide composition analysis of the chondroitin sulfate chain revealed that the five isomers differ in the numbers of 4-sulfated disaccharide units. Intriguingly, we detected the presence of multiple novel isomers with different numbers of non-sulfated disaccharide units even in the same charge isomer fraction. Our results demonstrate that UTI can vary in terms of both the degree of sulfation and the length of the low-sulfated chondroitin 4-sulfate chain.