Amino acid transamination in permeabilised cells of Lactobacillus helveticus, Lb. paracasei and Lb. danicus

Aminotransferase (AT) activity against 18 amino acids was studied in ten strains of three species of Lactobacillus. A method for permeabilisation of cells was developed using toluene and ethanol combined with mechanical treatment. It was found that the AT activities in the washed permeabilised cells (W-PC) corresponded well to that in cell-free extracts (CFE). The AT specificity pattern was species as well as strain dependant. Strains of Lb. helveticus had high specificity for aromatic amino acids (ArAA) and lower activity against branched-chain amino acids (BcAA) and Asp, while strains of Lb. paracasei subsp. paracasei degraded BcAA and Asp, but had a lower and variable specificity against ArAA. One of the Lb. paracasei strains was characterised by having very high AT activity against all three BcAA (Ile, Leu, Val) compared with any of the other Lb. paracasei strains tested. Strains of Lb. danicus, which is a newly discovered Lactobacillus species isolated from cheese, had up to about 20 times higher AT activity against Leu than Lb. paracasei and Lb. helveticus. The permeabilised cells of Lb. danicus had also considerably higher AT activity against ArAA than Lb. paracasei and Lb. helveticus strains, and also higher AT activity against Asp. All Lactobacillus strains tested had AT activity against Met, but at a much lower rate than against other amino acids. Results of this study also demonstrated a chemical reaction between alpha-ketoglutaric acid and Asp that was catalysed by pyridoxal-5-phosphate without any AT present.