The invention discloses a method for synthetizing L-
carnosine by a one-
step method and truncated L-
carnosine synthetase. According to the method, beta-
alanine, L-
histidine, ATP and
polyphosphate are used as raw materials, MgCl2 is used as an activator, L-
carnosine synthetase and
polyphosphate kinase are added, and through an enzymatic reaction under the condition of pH being 6.5-8.5 and the temperature being 30-45 DEG C, the carnosine is coupled, catalyzed and synthetized. According to the method disclosed by the invention,
escherichia coli is used for respectively expressing the truncated L-carnosine synthetase (of which the
amino acid sequence is as shown in SEQID No.3) and the
polyphosphate kinase, through purification, mixing is performed, a dual-
enzyme coupling system is formed, and the L-carnosine synthetase in truncated expression can catalyze the L-carnosine synthetized from beta-
alanine and L-
histidine; besides, accompanied with ATP
dephosphorylation, ADP is formed, the
polyphosphate kinase catalyzes polyphosphate transphosphorylation groups, and ATP is formed for the ADP, so that circulation and regeneration of the ATP can be realized; and through the dual-
enzyme couplingsystem, a reaction is performed under the appropriate reaction condition, so that carnosine is obtained. The method disclosed by the invention has the advantages that the raw materials are low in cost, the enzymatic conversion time is short, the operation is simple and convenient, and the production cost is low.