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. An enzymatic process for preparing fructose from a starch derivative, the process comprising the steps of:
(i) converting a starch derivative to glucose 1-phosphate (G1P) using an alpha glucan phosphorylase (αGP);
(ii) converting G1P to glucose 6-phosphate (G6P) using a phosphoglucomutase (PGM);
(iii) converting G6P to fructose 6-phosphate (F6P) using a phosphoglucoisomerase (PGI); and
(iv) converting F6P to fructose using a fructose 6-phosphate phosphatase (F6PP).
2. The process of claim 1 , wherein the starch derivative is prepared by:
(a) enzymatic hydrolysis of starch, by an isoamylase, a pullulanase, an alpha-amylase, or a combination thereof; or
(b) acid hydrolysis of starch.
3. The process of claim 1 , further comprising:
(v) converting degradation products of the process into longer maltooligosaccharides, using a 4-glucan transferase (4GT).
4. The process of claim 1 , wherein the process steps are conducted under at least one of the following process conditions:
at a temperature ranging from about 37° C. to about 85° C.,
at a pH ranging from about 5.0 to about 9.0, or
for about 0.5 hours to about 48 hours.
5. The process of claim 1 , wherein the process steps are conducted under at least one of the following process conditions:
without adenosine triphosphate (ATP) as a source of phosphate,
without nicotinamide adenosine dinucleotide,
at a phosphate concentration from about 0.1 mM to about 150 mM,
wherein phosphate is recycled, or
wherein step (iv) involves an energetically favorable chemical reaction.
6. The process of claim 5 , wherein phosphate is recycled and the phosphate produced by F6PP dephosphorylation of F6P is used in the process step of converting a starch derivative to G1P.
7. The process of claim 5 , wherein the step of converting F6P to fructose is an energetically favorable, irreversible phosphatase reaction.
8. The process of claim 1 wherein the starch derivatives are selected from the group consisting of amylose, amylopectin, soluble starch, amylodextrin, maltotriose, maltodextrin, maltose, and glucose and mixtures thereof.
9. The process of claim 1 , wherein the process steps are conducted in a single reaction vessel.