HISTIDINE CARBOXYLASE OF LEUCONOSTOC-OENOS-9204 - PURIFICATION, KINETIC-PROPERTIES, CLONING AND NUCLEOTIDE-SEQUENCE OF THE HDC GENE

Histidine decarboxylase (HDC) was purified to homogeneity from Leucono stoc oenos 9204, a wine lactic acid bacterium. Histidine decarboxylase comprised two subunits, respectively alpha and beta. The hdc gene was cloned and sequenced. The gene encodes a single polypeptide of 315 am ino acids, demonstrating that Leuc. oe nos 9204 HDC was synthesized as a precursor proHDC pi(6) (Mr 205 000). A cleavage between Ser-81 and Ser-82 generated the alpha (Mr 25 380) and beta (Mr 8840) chains, whic h suggested that the holoenzyme exists as a hexameric structure (alpha beta)(6). At the optimal pH of 4.8, the HDC activity exhibited a simp le Michaelis-Menten kinetic (K-m = 0.33 mmol l(-1), V-max = 17.8 mu mo l CO2 min(-1) mg(-1)), while at pH 7.6 it was sigmoidal (cooperativity index of 2). Histamine acted as a competitive inhibitor (K-i = 32 mmo l l(-1)). The similarities of these results with those described for o ther bacterial HDC support the assumption that the pyruvoyl enzymes ev olved from a common ancestral protein and hare similar catalytic mecha nisms. These results also confirmed that the main lactic acid bacteria l species responsible for malolactic fermentation in red wine is able to produce histamine. Bacteria carrying the HDC activity must be avoid ed during selection of strains for the production of malolactic starte rs.