masja nierop groot - Academia.edu (original) (raw)

Papers by masja nierop groot

Applied and Environmental Microbiology, 1999

We examined the involvement of Mn(II) in the conversion of phenylalanine to benzaldehyde in cell ... more We examined the involvement of Mn(II) in the conversion of phenylalanine to benzaldehyde in cell extracts of lactic acid bacteria. Experiments performed with Lactobacillus plantarum demonstrated that Mn(II), present at high levels in this strain, is involved in benzaldehyde formation by catalyzing the conversion of phenylpyruvic acid. Experiments performed with various lactic acid bacterial strains belonging to different genera revealed that benzaldehyde formation in a strain was related to a high Mn(II) level.

Applied and Environmental Microbiology, 1998

The production of benzaldehyde from phenylalanine has been studied in various microorganisms, and... more The production of benzaldehyde from phenylalanine has been studied in various microorganisms, and several metabolic pathways have been proposed in the literature for the formation of this aromatic flavor compound. In this study, we describe benzaldehyde formation from phenylalanine by using a cell extract of Lactobacillus plantarum . Phenylalanine was initially converted to phenylpyruvic acid by an aminotransferase in the cell extract, and the keto acid was further transformed to benzaldehyde. However, control experiments with boiled cell extract revealed that the subsequent conversion of phenylpyruvic acid was a chemical oxidation step. It was observed that several cations could replace the extract in the conversion of phenylpyruvic acid to benzaldehyde. Addition of Cu(II) ions to phenylpyruvic acid resulted not only in the formation of benzaldehyde, but also in the generation of phenylacetic acid, mandelic acid, and phenylglyoxylic acid. These compounds have been considered interm...

Applied and Environmental Microbiology, 2007

ABSTRACTThe pneumococcal serotype 14 polysaccharide was produced inLactococcus lactisby coexpress... more ABSTRACTThe pneumococcal serotype 14 polysaccharide was produced inLactococcus lactisby coexpressing pneumococcal polysaccharide type 14-specific genes (cpsFGHIJKL14) with the lactococcal regulatory and priming glucosyltransferase-encoding genes specific for B40 polysaccharide (epsABCDB40). The polysaccharide produced byLactococcuswas secreted in the medium, simplifying downstream processing and polysaccharide isolation from culture broth.

Current Opinion in Biotechnology, 1999

Everyone who has ever tried to radically change metabolic fluxes knows that it is often harder to... more Everyone who has ever tried to radically change metabolic fluxes knows that it is often harder to determine which enzymes have to be modified than it is to actually implement these changes. In the more traditional genetic engineering approaches 'bottle-necks' are pinpointed using qualitative, intuitive approaches, but the alleviation of suspected 'rate-limiting' steps has not often been successful. Here the authors demonstrate that a model of pyruvate distribution in Lactococcus lactis based on enzyme kinetics in combination with metabolic control analysis clearly indicates the key control points in the flux to acetoin and diacetyl, important flavour compounds. The model presented here (available at http ://jjj.biochem.sun.ac.za/wcfs.html) showed that the enzymes with the greatest effect on this flux resided outside the acetolactate synthase branch itself. Experiments confirmed the predictions of the model, i.e. knocking out lactate dehydrogenase and overexpressing NADH oxidase increased the flux through the acetolactate synthase branch from 0 to 75 % of measured product formation rates.

Applied and Environmental Microbiology, 1999

We examined the involvement of Mn(II) in the conversion of phenylalanine to benzaldehyde in cell ... more We examined the involvement of Mn(II) in the conversion of phenylalanine to benzaldehyde in cell extracts of lactic acid bacteria. Experiments performed with Lactobacillus plantarum demonstrated that Mn(II), present at high levels in this strain, is involved in benzaldehyde formation by catalyzing the conversion of phenylpyruvic acid. Experiments performed with various lactic acid bacterial strains belonging to different genera revealed that benzaldehyde formation in a strain was related to a high Mn(II) level.

Applied and Environmental Microbiology, 1998

The production of benzaldehyde from phenylalanine has been studied in various microorganisms, and... more The production of benzaldehyde from phenylalanine has been studied in various microorganisms, and several metabolic pathways have been proposed in the literature for the formation of this aromatic flavor compound. In this study, we describe benzaldehyde formation from phenylalanine by using a cell extract of Lactobacillus plantarum . Phenylalanine was initially converted to phenylpyruvic acid by an aminotransferase in the cell extract, and the keto acid was further transformed to benzaldehyde. However, control experiments with boiled cell extract revealed that the subsequent conversion of phenylpyruvic acid was a chemical oxidation step. It was observed that several cations could replace the extract in the conversion of phenylpyruvic acid to benzaldehyde. Addition of Cu(II) ions to phenylpyruvic acid resulted not only in the formation of benzaldehyde, but also in the generation of phenylacetic acid, mandelic acid, and phenylglyoxylic acid. These compounds have been considered interm...

Applied and Environmental Microbiology, 2007

ABSTRACTThe pneumococcal serotype 14 polysaccharide was produced inLactococcus lactisby coexpress... more ABSTRACTThe pneumococcal serotype 14 polysaccharide was produced inLactococcus lactisby coexpressing pneumococcal polysaccharide type 14-specific genes (cpsFGHIJKL14) with the lactococcal regulatory and priming glucosyltransferase-encoding genes specific for B40 polysaccharide (epsABCDB40). The polysaccharide produced byLactococcuswas secreted in the medium, simplifying downstream processing and polysaccharide isolation from culture broth.

Current Opinion in Biotechnology, 1999

Everyone who has ever tried to radically change metabolic fluxes knows that it is often harder to... more Everyone who has ever tried to radically change metabolic fluxes knows that it is often harder to determine which enzymes have to be modified than it is to actually implement these changes. In the more traditional genetic engineering approaches 'bottle-necks' are pinpointed using qualitative, intuitive approaches, but the alleviation of suspected 'rate-limiting' steps has not often been successful. Here the authors demonstrate that a model of pyruvate distribution in Lactococcus lactis based on enzyme kinetics in combination with metabolic control analysis clearly indicates the key control points in the flux to acetoin and diacetyl, important flavour compounds. The model presented here (available at http ://jjj.biochem.sun.ac.za/wcfs.html) showed that the enzymes with the greatest effect on this flux resided outside the acetolactate synthase branch itself. Experiments confirmed the predictions of the model, i.e. knocking out lactate dehydrogenase and overexpressing NADH oxidase increased the flux through the acetolactate synthase branch from 0 to 75 % of measured product formation rates.