Biomedical subjects

I Ncube

Publications and source records attributed to I Ncube.

4 recordsLinked to original sources

PubMed2004

Using heterogeneity to predict inhibitory network model characteristics.

From modeling studies it has been known for >10 years that purely inhibitory networks can produce synchronous output given appropriate balances of intrinsic and synaptic parameters. Several experimental studies indicate that synchronous activity produced by inhibitory networks is critical to the production of population rhythms associated with various behavioral states. Heterogeneity of inputs to inhibitory networks strongly affect their ability to synchronize. In this paper, we explore how the amount of input heterogeneity to two-cell inhibitory networks affects their dynamics. Using numerical simulations and bifurcation analyses, we find that the ability of inhibitory networks to synchronize in the face of heterogeneity depends nonmonotonically on each of the synaptic time constant, synaptic conductance and external drive parameters. Because of this, an optimal set of parameters for a given cellular model with various biophysical characteristics can be determined. We suggest that this could be a helpful approach to use in determining the importance of different, underlying biophysical details. We further find that two-cell coherence properties are maintained in larger 10-cell networks. As such, we think that a strategy of "embedding" small network dynamics in larger networks is a useful way to understand the contribution of biophysically derived parameters to population dynamics in large networks.

Biological Clocks↗

PubMed2002

Biodegradation of the organochlorine pesticide, lindane by a sub-tropical white rot fungus in batch and packed bed bioreactor systems.

The degradation of the organochlorine pesticide, lindane by a sub-tropical white rot fungus DSPM95 was studied in stationary batch and packed bed bioreactor systems. Pesticide concentrations of 5, 10, 20 and 40 ppm were used in batch cultures while concentrations of 1, 2, 5 and 10 ppm were used in the packed bed bioreactor. Biodegradation of 82 +/- 6% was achieved in batch cultures at concentrations of 5 and 10 ppm. The highest percent degradation achieved in the packed bed reactor was 81% at lindane concentrations of 1 and 2 ppm and the degradation decreased at 10 ppm. The amount of lindane degraded was directly proportional to the initial lindane concentration in the medium. Laccase and manganese peroxidase were produced in both stationary batch and in immobilised cultures, however high enzyme levels could not be sustained for long periods in the packed bed bioreactor.

Bioreactors↗

PubMed1999

Esterase and lipase activity in Jatropha curcas L. seeds.

Two new esterases (JEA and JEB) and a lipase (JL) were extracted from the seeds of Jatropha curas L. Lipase activity was only found during germination of the seeds and increased to a maximum after 4 days of germination. All enzymes were found to be most active in the alkaline range at around pH 8 and the purified (fractionated precipitation with ethanol and gel filtration) esterases were very stable at high temperatures. The molecular weight (SDS-PAGE) of both esterases was determined to be 21.6-23.5 kDa (JEA) and 30.2 kDa (JEB) and the isoelectric point was 5.7-6.1 for esterase JEA and 9.0 for esterase JEB. Most ions caused a negative influence on the activity of both esterases. Using p-nitrophenyl butyrate as a substrate JEA showed a K(m) of 0.02 mM and a v(max) of 0.26 micromol mg(-1) min(-1). Under the same conditions JEB showed a K(m) of 0.07 mM and a v(max) of 0.24 micromol mg(-1) min(-1). Both esterases hydrolyzed tributyrin, nitrophenyl esters up to a chain length of =C4 and naphtylesters up to a chain length =C6. In transesterification reactions, JL was found to be most active at very low water activities (0.2) and in high water activities, the lipase hydrolysed triglycerides into conversions above 80%. The lipase hydrolysed both short chain and long chain triglycerides at about the same rate but was inactive on alpha-methylbenzyl acetate. JL is a potentially useful biocatalyst in the hydrolysis of triglycerides in organic solvents.

Esterases↗

PubMed1995

Fatty acid selectivity of a lipase purified from Vernonia galamensis seed.

Vernonia galamensis is an annual herb whose seed oil contains high levels of an epoxy fatty acid, vernolic (cis-12,13-epoxy cis-9-octadecenoic) acid. The seed also contains lipase activity in the dormant state. A lipase was purified from the seed and its substrate specificity studied in isooctane. The lipase shows pronounced selectivity for the native triacylglycerol, trivernolin. The rate of hydrolysis of triolein, the corresponding non epoxy triacylglycerol, is only 3% of that of trivernolin. In the acidolysis of tricaprylin using a mixture of fatty acids, the Vernonia lipase also showed selectivity for vernolic acid. Michaelis-Menten kinetics of the hydrolysis of triacylglycerols revealed that the observed high selectivity of the Vernonia lipase for trivernolin was mainly due to a higher Vmax for trivernolin. The Vmax value for the hydrolysis of trivernolin was 5 times higher than that for triolein. This novel substrate specificity is an adaptation by the seed lipase to the triacylglycerols of the seed oil that contain up to 80% vernolic acid.

Epoxy Compounds↗