Biological post.

Anterior tooth fracture as a result of traumatic injuries, is frequently encountered in endodontic practice. Proper reconstruction of extensively damaged teeth can be achieved through the fragment reattachment procedure known as "biological restoration." This case report refers to the esthetics and functional recovery of extensively damaged maxillary central incisor through the preparation and adhesive cementation of "biological post" in a young patient. Biological post obtained through extracted teeth from another individual-represent a low-cost option and alternative technique for the morphofunctional recovery of extensively damaged anterior teeth.

Chemical modification of L-asparaginase from Cladosporium sp. for improved activity and thermal stability.

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 (kd), 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.

Purification, characterization and kinetic properties of extracellular L-asparaginase produced by Cladosporium sp.

L-asparaginase from Cladosporium sp. grown on wheat bran by SSF was purified. Enzyme appeared to be a trimer with homodimer of 37 kDa and another 47 kDa amounting to total mass of 121 kDa as estimated by SDS-PAGE and 120 kDa on gel filtration column. The optimum temperature and pH of the enzyme were 30 °C and 6.3, respectively with Vmax of 4.44 µmol/mL/min and Km of 0.1 M. Substrate specificity studies indicated that, L-asparaginase has greater affinity towards L-asparagine with substrate hydrolysis efficiency (Vmax/Km ratio) eightfold higher than that of L-glutamine. L-asparaginase activity in presence of thiols studied showed decrease in Vmax and increase in Km, indicating nonessential mode of inactivation. Among the thiols tested, ß-mercaptomethanol, exerted inhibitory effect, suggesting a critical role of disulphide linkages in maintaining a suitable conformation of the enzyme. Metal ions such as Ca(2+), Co(2+), Cu(2+), Mg(2+), Na(+), K(+) and Zn(2+) significantly affected enzyme activity whereas presence of Fe(3+), Pb(2+) and KI stimulated the activity. Detergents studied also enhanced L-asparaginase activity. In-vitro half-life of purified L-asparaginase in mammalian blood serum was 93.69 h. The enzyme inhibited acrylamide formation in potato chips by 96 % making it a potential candidate for food industry to reduce acrylamide content in starchy fried food commodities.