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Optimization of pH for high molecular weight pullulan (1993)

Lee, Ki Young ; Yoo, Young Je

Springer

Biotechnology letters 15 (1993), S. 1021-1024

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ISSN: 1573-6776

Source: Springer Online Journal Archives 1860-2000

Topics: Process Engineering, Biotechnology, Nutrition Technology

Notes: Summary Pullulan is a polysaccharide produced by Aureobasidium pullulans. In this study, the effect of pH on the molecular weight of pullulan was investigated. High concentration of pullulan was obtained when initial pH was 6. Pullulan having molecular weight of 500,000–600,000 was produced at initial pH of 3.0, while pullulan with molecular weight of 200,000–300,000 was produced at pH above 4.5. To obtain high molecular weight pullulan with high concentration, pH was initially controlled at pH 6, followed by pH shift from pH 6 to pH 3. Transition of pH at 2 days of fermentation was observed to be optimum. Higher molecular weight pullulan was also obtained when sucrose concentration was 50 g/l compared to the result obtained at initial sucrose concentration of 20 g/l. Sucrose concentration and pH of the fermentation broth seem to be important parameters in obtaining high molecular weight of pullulan.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00129930

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Gly-238-Ser substitution changes the substrate specificity of the SHV class A β-lactamases (1991)

Lee, Ki-Young ; Hopkins, John D. ; Syvanen, Michael ; [et al.]

New York, NY : Wiley-Blackwell

Proteins: Structure, Function, and Genetics 11 (1991), S. 45-51

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ISSN: 0887-3585

Keywords: third generation cephalosporins ; cefotaxime resistance ; enzyme structure-function ; Chemistry ; Biochemistry and Biotechnology

Source: Wiley InterScience Backfile Collection 1832-2000

Topics: Medicine

Notes: The SHV-type β-lactamase SHV-2A is related to SHV-1 by a Gly-238-Ser replacement. Strains carrying SHV-2A are resistant to the third generation cephems cefotaxime and ceftizoxime, whereas those that carry SHV-1 are sensitive to these drugs. We present a kinetic analysis of a SHV-1 and SHV-2A enzymes, with the goal of gaining insight into the role of residue 238 in hydrolyzing cefotaxime and ceftizoxime. SHV-2A shows altered kinetic properties for a number of other cephems that also have heterocyclic side chains at the amino position of the 7-aminocephalosporanic acid nucleus (R1 side chain), including a significantly higher kcat/Km than does SHV-1 for cephaloridine, cephalothin, and cefotiam. Two cephems with straight chain R1 substitutions, cephalosporin C and cephacetrile, are not hydrolyzed more efficiently by SHV-2A. These results indicate that the Ser-238-Gly substitution increases the affinity toward cephems with a heterocyclic ring in the R1 side chain. In addition, the data for ampicillin and benzylpenicillin show that addition of a nitrogen to the second carbon of the R1 side chain of a penem results in a lower kcat/Km for SHV-2A relative to SHV-1. These data strongly suggest that the previously proposed hydrogen bond formation between Ser-238 and the second carbon nitrogen of cefotaxime is not an important factor in hydrolysis by SHV-2A. We propose that the Gly-238 to Ser-238 replacement in SHV-2A has altered the hydrophobic pocket so that it can better accommodate cephems with bulky R1 side chains.

Additional Material: 3 Ill.