D-allulose, also known by the name D-psicose or just allulose, is a rare keto-sugar epimer of D-fructose in the third carbon (C3), and naturally occurs in small quantity in fruits such as grapes and figs. It is low ca...D-allulose, also known by the name D-psicose or just allulose, is a rare keto-sugar epimer of D-fructose in the third carbon (C3), and naturally occurs in small quantity in fruits such as grapes and figs. It is low calorie sweetener produced enzymatically from D-fructose by enzymes D-ketose 3-epimerase (DKEase) family. D-allulose has a similar taste, texture and functionality as sweetener comparing to high calorie sweetener sugar table sucrose. D-allulose is poorly metabolized in the body with minimal impact on blood sugar levels making it a natural low-calorie sweetener. This property makes D-allulose an attractive sweetener for diabetes and for body weight management. Laboratory studies on D-allulose intake demonstrated its safety with no significant adverse effects. United States Food and Drug Administration (FDA) has granted D-allulose the status of Generally Recognized as Safe (GRAS). Plus, it is considered safe for human consumption by regulatory organizations in other countries except in European Union due to their request for further laboratory testing. Maximum acceptable daily intake of D-allulose is 0.9 grams per kilogram body weight. Excessive intake for more than the recommended daily intake could lead to some side effects such as gastrointestinal discomfort or laxative effects. In general, D-allulose is considered one of the preferred natural low calories sweeteners for those seeking an alternative to table sugar sucrose.展开更多
D-Psicose 3-epimerase(DPEase)is demonstrated to be useful in the bioproduction of D-psicose,a rare hexose sugar,from D-fructose,found plenty in nature.Clostridium cellulolyticum H10 has recently been identified as a D...D-Psicose 3-epimerase(DPEase)is demonstrated to be useful in the bioproduction of D-psicose,a rare hexose sugar,from D-fructose,found plenty in nature.Clostridium cellulolyticum H10 has recently been identified as a DPEase that can epimerize D-fructose to yield D-psicose with a much higher conversion rate when compared with the conventionally used DTEase.In this study,the crystal structure of the C.cellulolyticum DPEase was determined.The enzyme assembles into a tetramer and each subunit shows a(β/α)8 TIM barrel fold with a Mn2+metal ion in the active site.Additional crystal structures of the enzyme in complex with substrates/products(D-psicose,D-fructose,D-tagatose and D-sorbose)were also determined.From the complex structures of C.cellulolyticum DPEase with D-psicose and D-fructose,the enzyme has much more interactions with D-psicose than D-fructose by forming more hydrogen bonds between the substrate and the active site residues.Accordingly,based on these ketohexosebound complex structures,a C3-O3 proton-exchange mechanism for the conversion between D-psicose and D-fructose is proposed here.These results provide a clear idea for the deprotonation/protonation roles of E150 and E244 in catalysis.展开更多
文摘D-allulose, also known by the name D-psicose or just allulose, is a rare keto-sugar epimer of D-fructose in the third carbon (C3), and naturally occurs in small quantity in fruits such as grapes and figs. It is low calorie sweetener produced enzymatically from D-fructose by enzymes D-ketose 3-epimerase (DKEase) family. D-allulose has a similar taste, texture and functionality as sweetener comparing to high calorie sweetener sugar table sucrose. D-allulose is poorly metabolized in the body with minimal impact on blood sugar levels making it a natural low-calorie sweetener. This property makes D-allulose an attractive sweetener for diabetes and for body weight management. Laboratory studies on D-allulose intake demonstrated its safety with no significant adverse effects. United States Food and Drug Administration (FDA) has granted D-allulose the status of Generally Recognized as Safe (GRAS). Plus, it is considered safe for human consumption by regulatory organizations in other countries except in European Union due to their request for further laboratory testing. Maximum acceptable daily intake of D-allulose is 0.9 grams per kilogram body weight. Excessive intake for more than the recommended daily intake could lead to some side effects such as gastrointestinal discomfort or laxative effects. In general, D-allulose is considered one of the preferred natural low calories sweeteners for those seeking an alternative to table sugar sucrose.
基金by grants from Science and Technology Projects of Tianjin(No.10YFYBJC00100)National High Technology Research and Development Program of China(863 Project)(Grant No.2012AA021503)+1 种基金Visiting Professorships for Senior International Scientists(No.2010T1S4)One Hundred Talents Project of The Chinese Academy of Sciences to RTG.
文摘D-Psicose 3-epimerase(DPEase)is demonstrated to be useful in the bioproduction of D-psicose,a rare hexose sugar,from D-fructose,found plenty in nature.Clostridium cellulolyticum H10 has recently been identified as a DPEase that can epimerize D-fructose to yield D-psicose with a much higher conversion rate when compared with the conventionally used DTEase.In this study,the crystal structure of the C.cellulolyticum DPEase was determined.The enzyme assembles into a tetramer and each subunit shows a(β/α)8 TIM barrel fold with a Mn2+metal ion in the active site.Additional crystal structures of the enzyme in complex with substrates/products(D-psicose,D-fructose,D-tagatose and D-sorbose)were also determined.From the complex structures of C.cellulolyticum DPEase with D-psicose and D-fructose,the enzyme has much more interactions with D-psicose than D-fructose by forming more hydrogen bonds between the substrate and the active site residues.Accordingly,based on these ketohexosebound complex structures,a C3-O3 proton-exchange mechanism for the conversion between D-psicose and D-fructose is proposed here.These results provide a clear idea for the deprotonation/protonation roles of E150 and E244 in catalysis.
