Biomedical subjects

M J Starrenburg

Publications and source records attributed to M J Starrenburg.

4 recordsLinked to original sources

PubMed1992

Isolation, characterization, and physiological role of the pyruvate dehydrogenase complex and alpha-acetolactate synthase of Lactococcus lactis subsp. lactis bv. diacetylactis.

The pyruvate dehydrogenase complex of Lactococcus lactis subsp. lactis bv. diacetylactis has a specific activity of 6.6 U/mg and a Km of 1 mM for pyruvate. The specific activities of E2 and E3 in the complex are 30 and 0.36 U/mg, respectively. The complex is very sensitive to NADH inhibition and consists of four subunits: E1 alpha (44 kDa), E1 beta (35 kDa), E2 (73 kDa), and E3 (60 kDa). The L. lactis alpha-acetolactate synthase has a specific activity of 103 U/mg and a Km of 50 mM for pyruvate. Thiamine pyrophosphate (Km = 3.2 microM) and divalent cations are essential for activity. The native enzyme measures 172 kDa and consists of 62-kDa monomers. The role of both enzymes in product formation is discussed in view of NADH inhibition and competition for pyruvate.

Acetolactate Synthase↗

PubMed1991

Citrate Fermentation by Lactococcus and Leuconostoc spp.

Citrate and lactose fermentation are subject to the same metabolic regulation. In both processes, pyruvate is the key intermediate. Lactococcus lactis subsp. lactis biovar diacetylactis homofermentatively converted pyruvate to lactate at high dilution (growth) rates, low pH, and high lactose concentrations. Mixed-acid fermentation with formate, ethanol, and acetate as products was observed under conditions of lactose limitation in continuous culture at pH values above 6.0. An acetoin/butanediol fermentation with alpha-acetolactate as an intermediate was found upon mild aeration in continuous culture and under conditions of excess pyruvate production from citrate. Leuconostoc spp. showed a limited metabolic flexibility. A typical heterofermentative conversion of lactose was observed under all conditions in both continuous and batch cultures. The pyruvate produced from either lactose or citrate was converted to d-lactate. Citrate utilization was pH dependent in both L. lactis and Leuconostoc spp., with maximum rates observed between pH 5.5 and 6.0. The maximum specific growth rate was slightly stimulated by citrate, in L. lactis and greatly stimulated by citrate in Leuconostoc spp., and the conversion of citrate resulted in increased growth yields on lactose for both L. lactis and Leuconostoc spp. This indicates that energy is conserved during the metabolism of citrate.

Journal Article↗

PubMed1990

Extraction of ribosomal RNA from soil for detection of Frankia with oligonucleotide probes.

Sequences of 16S rRNA of the nitrogen-fixing Frankia strain Ag45/Mut15 and the ineffective Frankia strain AgB1.9 were used to design a genus-specific oligonucleotide probe. Hybridization experiments of this Frankia probe and a second probe, specific for Nif+-Frankia strains only, were used to detect Frankia specific target sequences in RNA isolations from soil. A method is described for direct isolation of RNA from a loamy soil and a peat. Yields of about 10 ng RNA/g wet soil are obtained without detectable contamination with humic acids. Isolation of RNA after initial extraction of bacteria from soil resulted in significantly lower RNA yields, compared to the direct isolation procedure. Hybridization with both probes against rRNA isolations from Frankia-containing soil could detect target sequences within RNA isolations from 1 g wet soil with an estimated detection limit of 10(4) cells.

Actinomycetales↗

PubMed1990

Oligonucleotide Probes That Hybridize with rRNA as a Tool To Study Frankia Strains in Root Nodules.

Oligonucleotide probes that hybridize with specific sequences in variable regions of the 16S rRNA of the nitrogen-fixing actinomycete Frankia were used for the identification of Frankia strains in nodules. Frankia cells were released from plant tissue by grinding glutaraldehyde-fixed root nodules in guanidine hydrochloride solution. rRNA was obtained after sonication, precipitation with ethanol, and purification by phenolchloroform extraction. Degradation of rRNA, evident in Northern blots, did not affect hybridization with the oligonucleotides. Nodules of about 1 mg (fresh weight) provided sufficient rRNA for reliable detection of the Frankia strain. The utility of this rRNA extraction method was tested in a competition experiment between two effective Frankia strains on cloned Alnus glutinosa plants.

Journal Article↗