Kinetic and thermodynamic aspects of glucose-6-phosphate dehydrogenase activity and synthesis

Studies of crab digestive phospholipase acting on phospholipid monolayers: Activation by temperature

Secreted phospholipases A2 (sPLA2) are water-soluble lipolytic enzymes that act at the interface of organized lipid substrates, where the catalytic step is coupled to various interfacial phenomena as enzyme penetration, solubilisation of reaction products, lateral packing and loss of mechanical stability of organized assemblies of phospholipid molecule, among others. Using the monomolecular film technique, we compared the interfacial properties of crab digestive sPLA₂ (CDPL) with those of the porcine pancreatic one (PPPL). A kinetic study on the surface pressure dependency of the two sPLA₂ was performed using monomolecular films of three different substrates: di C₁₂-PC (1.2-dilauroyl-sn-glycerol-3-phosphocholine); di C₁₂-PG (1.2-dilauroyl-sn-glycerol-3-phosphoglycerol) and di C₁₂-PE (1.2-dilauroyl-sn-glycerol-3-phosphoethanolamine). The use of a substrate in monolayer state, during the catalytic reactions, allows us to monitor the effect of several physicochemical parameters by altering the "quality of interface". The effect of temperature on the hydrolysis rate of these substrates was also checked. Our results show that activities of both phospholipases were affected by the variation of the subphase temperature. CDPL was irreversibly inactivated by p-bromo-phenacyl bromide, the specific inhibitor of sPLA2. The hyperbolic catalytic behaviour observed was coherent with hopping mode of action, one of the two characteristic mechanisms of interfacial catalysis of sPLA2.

A simple strategy to effectively produce d-lactate in crude glycerol-utilizing Escherichia coli

BACKGROUND

Fed-batch fermentation has been conventionally implemented for the production of lactic acid with a high titer and high productivity. However, its operation needs a complicated control which increases the production cost.

RESULTS

This issue was addressed by simplifying the production scheme. Escherichia coli was manipulated for its glycerol dissimilation and d-lactate synthesis pathways and then subjected to adaptive evolution under high crude glycerol. Batch fermentation in the two-stage mode was performed by controlling the dissolved oxygen (DO), and the evolved strain deprived of poxB enabled production of 100 g/L d-lactate with productivity of 1.85 g/L/h. To increase productivity, the producer strain was further evolved to improve its growth rate on crude glycerol. The fermentation was performed to undergo the aerobic growth with low substrate, followed by the anaerobic production with high substrate. Moreover, the intracellular redox of the strain was balanced by fulfillment of the anaerobic respiratory chain with nitrate reduction. Without controlling the DO, the microbial fermentation resulted in the homofermentative production of d-lactate (ca. 0.97 g/g) with a titer of 115 g/L and productivity of 3.29 g/L/h.

CONCLUSIONS

The proposed fermentation strategy achieves the highest yield based on crude glycerol and a comparable titer and productivity as compared to the approach by fed-batch fermentation. It holds a promise to sustain the continued development of the crude glycerol-based biorefinery.

Response surface methodology for the evaluation of glucose-6-phosphate dehydrogenase enrichment process by soybean lecithin reversed micelles

Glucose-6-phosphate dehydrogenase (G6PD) present in Saccahromyces cerevisiae is an enzyme of the pentose pathway. An effective enrichment of this intracellular enzyme can be achieved with the reversed micellar methodology. In this work, this methodology was employed with soybean lecithin, a biocompatible surfactant. A factorial design was used to evaluate the influence of pH (A) and extraction runs (B) on the G6PD purification factor. After statistical analysis and process optimization, a mathematical model representing G6PD enrichment was obtained: Y=4.89-0.83A+0.092B+0.27AB-1.37B2 with an enzyme purification factor of about 5.2.