Abstract: The present invention relates to the field of biotechnologies. Disclosed are an enzyme composition for preparing ?-nicotinamide mononucleotide (NMN), and an application thereof. In the present invention, by using adenosine and nicotinamide as raw materials, D-ribose 1-phosphate and a nicotinamide ribose intermediate are generated under enzyme catalysis of an enzyme composition of a PNP enzyme and an NRK enzyme, and finally NMN is obtained; only two enzymes need to be involved in the whole reaction system, and the by-product adenine can be recycled. Moreover, only one molecule of ATP needs to be consumed for generating one molecule of NMN, thereby greatly reducing the process cost. The reaction of synthesizing NMN by NRK enzyme catalysis in the last step is irreversible, and thus, the substrate conversion rate can be greatly improved and the production cost can be further reduced.

Abstract: The present invention relates to the technical field of biosynthesis, and in particular to a method for preparing S-nicotine. Amine oxidase is utilized to oxidize 1-methylpyrrolidine into corresponding imine, and then the imine and nicotinic acid are condensed and decarboxylated under the catalysis of nicotine synthetase to obtain a final product S-nicotine. The S-nicotine having specific chirality can be obtained by means of two-step reaction in a reaction system, the synthetic route is short, the yield is high, the reaction conditions are mild, and large-scale production is easy to achieve; moreover, raw materials are wide in source, low in price, low in production cost and environmentally friendly, the production cost of nicotine is remarkably reduced, and the requirements of current green industrial production can be better satisfied.

Abstract: The present invention relates to the technical field of biochemistry. Disclosed are a mutant enzyme, the use thereof and a process for preparing a tripeptide by using an enzymatic method. The mutant enzyme comprises: glycine and L-histidine ligase GHS, and tripeptide ligase HKS; or a fusion enzyme of the two. Glycine and L-histidine ligase activity is achieved by means of modifying an Lal enzyme, so as to obtain the GHS enzyme; and the ability for synthesizing dipeptide glycine-L-histidine and L-lysine is achieved by means of using a gshB enzyme, so as to obtain the HKS enzyme. On this basis, the GHS enzyme is further fused with the HKS enzyme by means of using a polypeptide chain, and then a bifunctional enzyme GHKS that links glycine, L-histidine and L-lysine in one step can be constructed, so that a tripeptide is conveniently prepared with a high yield.