CHEMICAL MODIFICATION OF L-ASPARAGINASE FROM Cladosporium sp. FOR IMPROVED ACTIVITY AND THERMAL STABILITY

Abstract

L-Asparaginase (ASNase), an antileukemia enzyme, is facing problems with antigenicity in the blood. Modification of L-asparaginase from Cladosporium sp. was tried to obtain improved stability and improved functionality. In our experiment, modification of the enzyme was tried with bovine serum albumin, ovalbumin by crosslinking using glutaraldehyde, N-bromosuccinimide, and mono-methoxy polyethylene glycol. Modified enzymes were studied for activity, temperature stability, rate constants (k_d), and protection to proteolytic digestion. Modification with ovalbumin resulted in improved enzyme activity that was 10-fold higher compared to native enzyme, while modification with bovine serum albumin through glutaraldehyde cross-linking resulted in high stability of L-asparaginase that was 8.5- and 7.62-fold more compared to native enzyme at 28°C and 37°C by the end of 24 hr. These effects were dependent on the quantity of conjugate formed. Modification also markedly prolonged L-asparaginase half-life and serum stability. N-Bromosuccinimide-modified ASNase presented greater stability with prolonged in vitro half-life of 144 hr to proteolytic digestion relative to unmodified enzyme (93 h). The present work could be seen as producing a modified L-asparaginase with improved activity and stability and can be a potential source for developing therapeutic agents for cancer treatment.

Keywords:

• chemical modification
• in vitro half-life
• L-asparaginase
• thermal stability
• tryptophan

ACKNOWLEDGMENTS

The authors gratefully acknowledge the director, CFTRI, for providing necessary laboratory facilities. Sincere thanks are offered by the first author to the Council of Scientific and Industrial Research (CSIR), New Delhi, India, for providing a senior research fellowship.

Notes

Note. Specific activity was measured without any incubation and the units were expressed in U/mg.

Note. Units of half-life are expressed in hours (hr) and inactivation rate constant k_d is expressed in per hour (1/hr).

Note. All ASNase (native and modified) were studied for thermal deactivation kinetics. Inactivation energy (E_d), Free energy of inactivation (ΔG*), Inactivation enthalpy (ΔH*), and Inactivation entropy (ΔS*) were calculated for both the temperatures (28°C and 37°C).