| 1. |
- Agnantiari, G., et al.
(författare)
-
A Purified α-galactosidase from aspergillus niger with enhanced kinetic characteristics
- 1991
-
Ingår i: Acta Biotechnologica. - : Wiley. - 0138-4988 .- 1521-3846. ; 11:5, s. 479-484
-
Tidskriftsartikel (refereegranskat)abstract
- Extracellular α-galactosidase from Aspergillus niger was purified 128-fold over the crude extract by gel filtration, ion exchange chromatography and chromatofocusing. Certain substrates and end products affected enzyme activity. Among the former p-nitrophenyl-α-galactopyranoside (PNPG) inhibited the enzyme at 1.4 mM while melibiose did not inhibit α-galactosidase at concentrations up to 50 mM. Enzymic end products such as glucose did not inhibit the enzyme at concentrations up to 100 mM while galactose exhibited a competitive inhibition with a Ki = 1.29 mM. The kinetic characteristics of the enzyme compared favourably to other microbial α-galactosidases and make it suitable for food process applications.
|
|
| 2. |
- Caridis, K A, et al.
(författare)
-
Control of catalase production and purity by altering certain nutritional factors of Alternaria alternata growth medium
- 1991
-
Ingår i: Biotechnology letters. - 0141-5492 .- 1573-6776. ; 13:1, s. 35-38
-
Tidskriftsartikel (refereegranskat)abstract
- Both activity level of catalase and presence of glucose oxidase as an impurity were controlled by the type and concentration of nitrogen and carbon source in the culture medium of Alternaria alternata. It was possible to produce glucose oxidase-free catalase at activity levels competing favourably with those reported for other catalase hyperproducing microorganisms.
|
|
| 3. |
- Caridis, Konstantina-Anna, et al.
(författare)
-
Simultaneous production of glucose oxidase and catalase by Alternaria alternata
- 1991
-
Ingår i: Applied Microbiology and Biotechnology. - 0175-7598 .- 1432-0614. ; 34:6, s. 794-797
-
Tidskriftsartikel (refereegranskat)abstract
- A number of factors affecting simultaneous production of cell-bound glucose oxidase and catalase by the fungus Alternaria alternata have been investigated. Consecutive optimization of the type and concentration of nitrogen and carbon source, the initial pH and growth temperature resulted in a simultaneous increase in glucose oxidase and catalase by 780% and 68% respectively. Two second-order equations, describing the combined effect of pH and temperature on the activity of each enzyme, revealed that glucose oxidase had its optima at pH 7.9 and 32.3°C and catalase at pH 8.5 and 18.1°C. Under certain growth conditions, yields as high as 23.5 and 18,100 units/g carbon source for glucose oxidase and catalase, respectively, were simultaneously obtained.
|
|
| 4. |
- Christakopoulos, Paul, et al.
(författare)
-
Direct conversion of sorghum carbohydrates to ethanol by a mixed microbial culture
- 1993
-
Ingår i: Bioresource Technology. - 0960-8524 .- 1873-2976. ; 45:2, s. 89-92
-
Tidskriftsartikel (refereegranskat)abstract
- The carbohydrates of sweet sorghum were directly converted to ethanol by a mixed culture of Fusarium oxysporum F3 and Saccharomyces cerevisiae 2541. A number of factors affecting this bioconversion was studied. Optimum ethanol yields of 33·2 g/100 g of total sorghum carbohydrates, corresponding to 10·3 g/100 g of fresh stalks, were obtained. These values represented 68·6% of the theoretical yield based on total polysaccharides and exceeded that based on oligosaccharides of sorghum by 53·7%. The results demonstrated that more than half of the sorghum polysaccharides were directly fermented to ethanol, thus making the process worthy of further investigation.
|
|
| 5. |
- Christakopoulos, Paul, et al.
(författare)
-
Direct conversion of straw to ethanol by Fusarium oxysporum : Effect of cellulose crystallinity
- 1991
-
Ingår i: Enzyme and microbial technology. - 0141-0229 .- 1879-0909. ; 13:3, s. 272-274
-
Tidskriftsartikel (refereegranskat)abstract
- Wheat straw was successfully fermented to ethanol by Fusarium oxysporum F3 in a one-step process. Cellulose crystallinity was found to be a major factor in the bioconversion process. Ethanol yields increased linearly with decreasing crystallinity index. Approximately 80% of straw carbohydrates were converted directly to ethanol with a yield of 0.28 g ethanol/g−1 of straw when the crystallinity index was reduced to 23.6%.
|
|
| 6. |
- Christakopoulos, Paul, et al.
(författare)
-
Direct ethanol conversion of pretreated straw by Fusarium oxysporum
- 1991
-
Ingår i: Bioresource Technology. - : Elsevier BV. - 0960-8524 .- 1873-2976. ; 35:3, s. 297-300
-
Tidskriftsartikel (refereegranskat)abstract
- Factors affecting the direct conversion of alkali pretreated straw to ethanol by Fusarium oxysporum F3 were investigated and the alkali level used for pretreatment and the degree of delignification of straw were found to be the most important. A linear correlation between ethanol yield and both the degree of straw delignification and the alkali level was observed. At optimum delignified straw concentration (4% w/v), a maximum ethanol yield of 0·275 g ethanol g−1 of straw was obtained corresponding to 67·8% of the theoretical yield.
|
|
| 7. |
- Christakopoulos, Paul, et al.
(författare)
-
Exceptionally thermostable α- and β-galactosidase from Aspergillus niger separated in one step
- 1990
-
Ingår i: Process Biochemistry. - 1359-5113 .- 1873-3298. ; 25:6, s. 210-212
-
Tidskriftsartikel (refereegranskat)abstract
- Extracellular alpha- and-beta-galactosidases from a strain of Aspergillus niger were separated and purified in one step by cation exchange chromatography. Both enzymes had acidic pH (3.5-4.0) and high temperature (65-degrees-C) optima and an exceptionally high thermostability. Thus, -alpha-galactosidase had an activity half-time of 104 min at 60-degrees-C whereas at the same temperature the respective value for-beta-galactosidase was 835 min. At optimum conditions of activity the apparent K(m) values of alpha- and beta-galactosidase were 0.44mM and 1.1mM respectively. Both the high temperature optima and thermostability properties of the enzymes make them particularly suitable for high temperature processes.
|
|
| 8. |
- Christakopoulos, Paul, et al.
(författare)
-
On the mechanism of direct conversion of cellulose to ethanol by Fusarium oxysporum : Effect of cellulase and β-glucosidase
- 1990
-
Ingår i: Applied Microbiology and Biotechnology. - 0175-7598 .- 1432-0614. ; 33:1, s. 18-20
-
Tidskriftsartikel (refereegranskat)abstract
- The effects of the three main enzymes involved in cellulose saccharification, namely cellobiohydrolase, carboxymethylcellulase and beta-glucosidase, on the direct conversion of cellulose to ethanol by Fusarium oxysporum F3 were investigated. Ethanol production was not affected when the activity of the former two enzymes was varied within a wide range. By contrast, beta-glucosidase markedly affected ethanol production showing an optimum level of 0.7-0.8 unit/ml growth medium. A significant decrease of cellulose bioconversion time to ethanol was obtained when beta-glucosidase activity was adjusted to this optimal level at the beginning of the fermentation process.
|
|
| 9. |
- Christakopoulos, Paul, et al.
(författare)
-
Optimization of β-glucosidase catalysed synthesis of trisaccharides from cellobiose and gentiobiose
- 1994
-
Ingår i: Biotechnology letters. - 0141-5492 .- 1573-6776. ; 16:6, s. 587-592
-
Tidskriftsartikel (refereegranskat)abstract
- Purified β-Glucosidase from Fusarium oxysporum catalysed the hydrolysis and transglycosylation reactions in the presence of cellobiose and gentiobiose. The product of the latter reaction was mainly a triose. The time of incubation, pH and substrate concentration for transglycosylation reaction were optimised. Under optimal conditions, the concentration of glucose and triose reached approximately 15–20 % of the initial substrate concentration. These results suggested that β-glucosidase from F.oxysporum is an ideal enzyme for the synthesis of triose in reasonable quantities.
|
|
| 10. |
- Christakopoulos, Paul, et al.
(författare)
-
Production and characterization of extracellular lipase from Calvatia gigantea
- 1992
-
Ingår i: Applied Microbiology and Biotechnology. - 0175-7598 .- 1432-0614. ; 38:2, s. 194-197
-
Tidskriftsartikel (refereegranskat)abstract
- A number of factors affecting production of extracellular lipase by the edible fungus Calvatia gigantea were investigated. Consecutive optimization of carbon and nitrogen sources, initial pH of culture medium and growth temperature resulted in an increase in lipase activity of 87%. Under optimum conditions, activities as high as 22.4 units ml−1 of culture medium were obtained, competing favourably with most activities reported for other lipase hyperproducing microorganisms. The enzyme was optimally active at pH 7.0 and 30°C and had, at optimum pH, half-lives of 75.7 and 22.9 min at 45 and 55°C. Both high activity and kinetic characteristics of the enzyme make this process worthy of further investigation.
|
|
