Relationship between plasmin-trypsin-inhibitory and sialyltransferase activities

Area of Science:

• Biochemistry
• Enzymology
• Cell Biology

Background:

• Soluble sialyltransferase (STase) activity released from rat jejunal slices depends on heparin-binding fraction (HBF) or trypsin-binding protein (TBP).
• HBF and TBP inhibit trypsin and plasmin, while galactosyltransferase (GTase) activity is unaffected.
• Previous work established a link between STase activity and protease inhibition.

Purpose of the Study:

• To investigate the relationship between sialyltransferase (STase) activity and protease inhibitory activity.
• To determine if protease inhibitors influence STase activity in jejunal and hepatocyte incubations.

Main Methods:

• Incubation of rat jejunal slices and hepatocytes in media supplemented with heat-inactivated serum from control (HCS) or turpentine-treated rats (HTS).
• Measurement of soluble STase and galactosyltransferase (GTase) activities in incubation media.
• Assessment of plasmin-trypsin-inhibitory activity in serum and the effect of trypsin-binding protein (TBP) on STase activity stability.

Main Results:

• Heat-inactivated serum from turpentine-treated rats (HTS) showed higher protease inhibitory activity and significantly increased STase activity in jejunal and hepatocyte incubations compared to HCS.
• Serum STase activity was higher in turpentine-treated rats.
• Trypsin-binding protein (TBP) prevented the decrease in STase activity during incubation at 37°C, indicating a protective role.

Conclusions:

• Protease inhibitory activity, particularly from TBP, is linked to enhanced and stabilized soluble STase activity.
• Galactosyltransferase (GTase) activity is independent of protease inhibitory activity.
• Findings suggest a functional interplay between protease inhibition and sialyltransferase activity in biological systems.