A method of providing and sustaining a difference in pH of a first reaction of an immobilized enzyme and a second reaction in a bulk liquid surrounding the immobilized enzyme is carried out with a bilayer pellet containing coimmobilized enzymes. The pellet can contain an enzyme that produces a desired product immobilized in an inner core and urease immobilized in an outer layer. The bulk liquid contains urea and a substrate for the enzyme in the core, and has an acidic pH. The urease reacts with urea diffusing into the outer layer from the bulk liquid to produce ammonia. The ammonia consumes hydrogen ions diffusing into the inner core from the acidic bulk liquid. This provides the enzyme in the inner core with a pH higher than the acidic pH of the bulk liquid suitable for the enzyme to react with the substrate as it diffuses into the inner core. In a preferred embodiment, simultaneous isomerization of xylose to xylulose and fermentation of xylulose to ethanol is carried out with a bilayer pellet containing xylose isomerase in the core and yeast in the bulk liquid. The isomerization occurs at an optimum pH of 7.0 to 8.0 and the fermentation occurs at an optimum pH of 4.0 to 5.0.

Document Type


Primary Class


Secondary Class

435/94; 435/161; 435/162; 435/175; 435/180; 435/182

Application Number


Filing Date

September 1993

Patent Number



The University of Toledo

Publication Date


Patent Country





The University of Toledo


University of Toledo Libraries

Digital Publisher

Digital Initiatives


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Rights Statement

No Copyright - United States. URI: http://rightsstatements.org/vocab/NoC-US/1.0/
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