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W Harder

Publications and source records attributed to W Harder.

122 records · Page 7Linked to original sources
PubMed1971

The biosynthesis of serine and glycine in Pseudomonas AM1 with special reference to growth on carbon sources other than C1 compounds.

1. A mutant, 20S, of Pseudomonas AM1 was obtained that requires a supplement of serine to grow on succinate, lactate or ethanol. This mutant lacks phosphoserine phosphatase and revertants to wild-type phenotype regained this enzymic activity showing that the phosphorylated pathway of serine biosynthesis is necessary for growth on these three substrates. 2. The requirement for supplemental serine by mutant 20S could be met by glycine, suggesting that Pseudomonas AM1 can obtain C(1) units from glycine. 3. Mutant 20S grows on C(1) compounds at a lower rate compared with the wild type. Supplementation with serine stimulated the growth rate of the mutant suggesting that the phosphorylated pathway of serine biosynthesis plays some role, but not an essential role, during growth on C(1) compounds. 4. A mutant, 82G, was obtained that requires a supplement of glycine to grow on succinate, lactate or ethanol. When grown in such supplemented media, the mutant lacks serine hydroxymethyltransferase and revertants to wild-type phenotype regained enzymic activity showing that during growth on succinate, lactate or ethanol, glycine is made from serine via serine hydroxymethyltransferase, and that the organism can obtain C(1) units from glycine. 5. Mutant 82G grew on methanol and then contained serine hydroxymethyltransferase suggesting that this enzyme is necessary for growth on C(1) compounds and that Pseudomonas AM1 may synthesize two such enzymes, one used in growth on C(1) compounds, the other used in growth on other substrates. Mutant 82G might lack the latter enzyme. 6. Phosphoglycerate dehydrogenase is specifically inhibited by l-serine and the regulatory implications of this are discussed.

Carbon↗
PubMed1971

Aspects of glycine and serine biosynthesis during growth of Pseudomonas AM1 on C compounds.

1. Methanol or formate can replace serine or glycine as supplements for growth on succinate of the auxotrophic mutants 20S and 82G of Pseudomonas AM1, showing that the organism can synthesize glycine and serine in net fashion from C(1) units. 2. Double mutants of Pseudomonas 20S and 82G have been prepared (20ST-1 and 82GT-1) that are unable to grow on succinate+1mm-glyoxylate, succinate+2mm-methanol or methanol alone. 3. Mutants 20ST-1 and 82GT-1 lacked serine-glyoxylate aminotransferase activity, and revertants to the phenotype of 20S and 82G regained serine-glyoxylate aminotransferase activity. A total revertant of 82GT-1 to wild-type phenotype regained activities of serine hydroxymethyltransferase and serine-glyoxylate aminotransferase. 4. The activity of serine-glyoxylate aminotransferase in methanol-grown Pseudomonas AM1 is eightfold higher than in the succinate-grown organism. 5. The combined results show that in Pseudomonas AM1 serine-glyoxylate aminotransferase is necessary for growth on C(1) compounds and is involved in the conversion of methanol into glycine via glyoxylate. 6. It is suggested that the phosphorylated pathway of serine biosynthesis from phosphoglycerate replenishes the supply of alpha-amino groups necessary for the flow of glyoxylate through the main assimilatory pathway during growth on C(1) compounds.

Carbon↗
PubMedDate not supplied

Occurrence of peroxisomal membrane proteins in methylotrophic yeasts grown under different conditions.

We have studied the substructure and polypeptide composition of the peroxisomal membranes in two methylotrophic yeasts in relation to different growth conditions. The results obtained indicated that no significant ultrastructural differences existed between the membranes of variously grown cells. The presence of specific peroxisomal membrane proteins (PMPs) was studied biochemically. On sodium dodecyl sulphate-polyacrylamide gels of purified microbody membranes isolated from methanol-grown Hansenula polymorpha, prominent protein bands were observed at 22, 31, 35, 42, 49 and 51 kD. These proteins were also present when the cells were grown in media containing ethanol and/or ethylamine. Apart from these, several other PMPs were specifically induced under these conditions, namely 24, 29, 37 and 62 kD proteins. The polypeptide composition of peroxisomal membranes from H. polymorpha was compared with that of another methylotroph, Candida biodinii. In the latter organism a specific PMP with a molecular weight of 23 kD was induced during growth on D-alanine instead of ammonium sulphate as the nitrogen source.

Candida↗
PubMedDate not supplied

Immunocytochemical demonstration of the peroxisomal ATPase of yeasts.

The presence of an ATPase on yeast peroxisomal membranes was studied by immunological methods. Western blot analysis of purified peroxisomal membranes from several yeasts revealed distinct cross-reaction with specific antibodies against the F1-part or the beta-subunit of the mitochondrial ATPase of Saccharomyces cerevisiae. This was not due to mitochondrial contamination as was demonstrated by analytical sucrose gradient centrifugation. Protein A-gold labelling carried out on Lowicryl-embedded methanol-grown Hansenula polymorpha using these antibodies did not result in significant staining. However, when organelles isolated from this yeast were successively incubated with antibodies and protein A-gold prior to embedding, specific labelling was observed on both the peroxisomal membrane and the membrane of damaged mitochondria but not on intact mitochondria. Specific labelling of the peroxisomal membrane was confirmed by freeze-fracture immunocytochemistry. In addition to the peroxisomal membrane, the mitochondrial membrane was also labelled in these experiments. Freeze-fracture immunocytochemistry was also successful for the localization of peroxisomal matrix proteins, e.g. alcohol oxidase and dihydroxyacetone synthase, and of mitochondrial membrane proteins, e.g. cytochrome c oxidase.

Adenosine Triphosphatases↗
PubMedDate not supplied

Transformation of carbon tetrachloride under sulfate reducing conditions.

The removal of carbon tetrachloride under sulfate reducing conditions was studied in an anaerobic packed-bed reactor. Carbon tetrachloride, up to a concentration of 30 microM, was completely converted. Chloroform and dichloromethane were the main transformation products, but part of the carbon tetrachloride was also completely dechlorinated to unknown products. Gram-positive sulfate-reducing bacteria were involved in the reductive dechlorination of carbon tetrachloride to chloroform and dichloromethane since both molybdate, an inhibitor of sulfate reduction, and vancomycin, an inhibitor of gram-positive bacteria completely inhibited carbon tetrachloride transformation. Carbon tetrachloride transformation by these bacteria was a cometabolic process and depended on the input of an electron donor and electron acceptor (sulfate). The rate of carbon tetrachloride transformation by sulfate reducing bacteria depended on the type of electron donor present. A transformation rate of 5.1 nmol x ml(-1) x h(-1) was found with ethanol as electron donor. At carbon tetrachloride concentrations higher than 18 microM, sulfate reduction and reductive dechlorination of carbon tetrachloride decreased and complete inhibition was observed at a carbon tetrachloride concentration of 56.6 microM. It is not clear what type of microorganisms were involved in the observed partial complete dechlorination of carbon tetrachloride. Sulfate reducing bacteria probably did not play a role since inhibition of these bacteria with molybdate had no effect on the complete dechlorination of carbon tetrachloride.

Bacteria↗