Enzymatic production of hexoses
Disclosed herein are methods of producing hexoses from saccharides by enzymatic processes. The methods utilize fructose 6-phosphate and at least one enzymatic step to convert it to a hexose.
1. A process for preparing allose from a saccharide, the process comprising:
converting fructose 6-phosphate (F6P) to psicose 6-phosphate (P6P),catalyzed by a psicose 6-phosphate 3-epimerase (P6PE);
converting the P6P to allose 6-phosphate (A6P) catalyzed by an allose 6-phosphate isomerase (A6PI); and
converting the A6P to allose catalyzed by an allose 6-phosphate phosphatase (A6PP).
2. The process of claim 1 , further comprising a step of converting glucose 6-phosphate (G6P) to the F6P, wherein the step is catalyzed by a phosphoglucoisomerase (PGI).
3. The process of claim 2 , further comprising the step of converting glucose 1-phosphate (G1P) to the G6P, wherein the step is catalyzed by a phosphoglucomutase (PGM).
4. The process of claim 3 , further comprising the step of converting a saccharide to the G1P, wherein the step is catalyzed by at least one enzyme, wherein the saccharide is starch, a starch derivative, or sucrose.
5. The process of claim 4 , wherein the at least one enzyme in the step of converting a saccharide to the G1P is selected from the group consisting of an alpha-glucan phosphorylase (αGP), a sucrose phosphorylase, and mixtures thereof.
6. The process of claim 4 , wherein the saccharide is starch or a derivative thereof selected from the group consisting of amylose, amylopectin, soluble starch, amylodextrin, maltodextrin, maltose, and glucose, and mixtures thereof.
7. The process of claim 6 , further comprising the step of converting starch to a starch derivative wherein the starch derivative is prepared by enzymatic hydrolysis of starch or by acid hydrolysis of starch.
8. The process of claim 6 , wherein 4-glucan transferase (4GT) is added to the process.
9. The process of claim 4 , wherein the starch derivative is prepared by enzymatic hydrolysis of starch catalyzed by isoamylase, pullulanase, alpha-amylase, or a combination thereof.
10. The process of claim 1 , wherein the process steps are conducted at a temperature ranging from about 37° C. to about 85° C., at a pH ranging from about 5.0 to about 9.0, and/or for about 0.5 hours to about 48 hours.
11. The process of claim 1 , wherein the process steps are conducted in a single bioreactor.
12. The process of claim 1 , wherein the process steps are conducted ATP-free, NAD(P)(H)-free, at a phosphate concentration from about 0.1 mM to about 150 mM, the phosphate is recycled, and/or the catalysis by the hexose-specific phosphatase involves an energetically favorable chemical reaction.