Biomedical subjects

Paramasamy Gunasekaran

Publications and source records attributed to Paramasamy Gunasekaran.

5 recordsLinked to original sources

PubMed2004

Recent biotechnological interventions for developing improved penicillin G acylases.

Penicillin G acylase (PAC; EC 3.5.1.11) is the key enzyme used in the industrial production of beta-lactam antibiotics. This enzyme hydrolyzes the side chain of penicillin G and related beta-lactam antibiotics releasing 6-amino penicillanic acid (6-APA), which is the building block in the manufacture of semisynthetic penicillins. PAC from Escherichia coli strain ATCC 11105, Bacillus megaterium strain ATCC 14945 and mutants of these two strains is currently used in industry. Genes encoding for PAC from various bacterial sources have been cloned and overexpressed with significant improvements in transcription, translation and post-translational processing. Recent developments in enzyme engineering have shown that PAC can be modified to gain conformational stability and desired functionality. This review provides an overview of recent advances in the production, stabilization and application of PAC, highlighting the recent biotechnological approaches for the improved catalysis of PAC.

Journal Article↗

PubMed2004

Purification and characterization of a low molecular weight endoxylanase from solid-state cultures of alkali-tolerant Aspergillus fischeri.

A low molecular weight, alkaline-stable endoxylanase (XylB) was purified to homogeneity from solid-state culture of Aspergillus fischeri Fxn1. XylB had a molecular mass of 13 kDa which is the lowest of reported xylanases. Optimal activity was at pH 6 and 55 degrees C. XylB was stable from pH 4.5 to 10 and up to 60 degrees C. It was non-glycosylated. The apparent K(m) and V(max) values of XylB on birch wood xylan were 0.53 mg ml(-1) and 0.2 mmol min-1 mg-1, respectively. The activity of XylB was not inhibited by Cd2+, Zn2+, Co2+, EDTA, iodoacetamide, beta-mercaptoethanol and acetic anhydride but strongly inhibited by 10 mm of N-bromosuccinimide, Hg2+, Pb2+ and p-hydroxymercuric benzoate. XylB is an endoxylanase since it hydrolysed xylan resulting the formation of xylo-oligomers but not of xylose residues.

Alkalies↗

PubMed2003

Inhibition of proteases during fermentation improves xylanase production by alkali tolerant Aspergillus fumigatus ARl.

An alkali-tolerant Aspergillus fumigatus ARl produced a high level of xylanase (228 U/ml) at 42 h of submerged fermentation at pH 9.0. During later culture periods, xylanase activity declined considerably and reached 45 U/ml at 90 h. This trend is because of proteolytic degradation of xylanases since A. fumigatus co-produced multiple proteases with high activity (120-159 U/ml) during submerged fermentation. Xylanase and protease were found to be active over a wide range of pH from 5.5 to 9.0. In contrast, protease lost its activity completely in the presence of CuSO4 (25 mM) while xylanase remained active. The selective inhibition of proteases by the addition of CuSO4 to the culture medium prevented proteolytic degradation of xylanase and improved the production of xylanase by 3-fold.

Journal Article↗

PubMed2003

Serine substitution for cysteine residues in levansucrase selectively abolishes levan forming activity.

Levansucrase is responsible for levan formation during sucrose fermentation of Zymomonas mobilis, and this decreases the efficiency of ethanol production. As thiol modifying agents decrease levan formation, a role for cysteine residues in levansucrase activity has been examined using derivatives of Z. mobilis levansucrase that carry serine substitutions of cysteine at positions 121, 151 or 244. These substitutions abolished the levan forming activity of levansucrase whilst only halving its activity in sucrose hydrolysis. Thus, polymerase and hydrolase activities of Z. mobilis levansucrase are separate and have different requirements for the enzyme's cysteine residues.

Amino Acid Sequence↗

PubMed2002

Beta-fructofuranosidase production by 2-deoxyglucose resistant mutants of aspergillus niger in submerged and solid-state fermentation.

Aspergillus niger produces extracellular beta-fructofuranosidase under submerged (SmF) and solid state fermentation (SSF) conditions. After UV mutagenesis of conidiospores of A. niger, 2-deoxyglucose (10 g/l) resistant mutants were isolated on Czapek's minimal medium containing glycerol as a carbon source and the mutants were examined for improved production of beta-fructofuranosidase in SmF and SSF conditions. One of such mutant DGRA-1 overproduced beta-fructofuranosidase in both SmF and SSF conditions. In SmF, the mutant DGRA-1 showed higher beta-fructofuranosidase productivity (110.8 U/l/hr) than the wild type (48.3 U/l/hr). While in SSF the same strain produced 322 U/l/hr of beta-fructofuranosidase, 2 times higher than that of wild type (154.2 U/l/hr). In SmF, both wild type and mutants produced relatively low level of beta-fructofuranosidase in medium containing sucrose with glucose than from the sucrose medium. However in SSF, the DGRA-1 mutant grown in sucrose and sucrose+ glucose did not show any difference with respect to beta-fructofuranosidase production. These results indicate that the catabolite repression of beta-fructofuranosidase synthesis is observed in SmF whereas in SSF such regulation was not prominent.

Aspergillus niger↗