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

摘要

Aminotransferase (AT) activity against 18 amino acids was studied in 10 strains of 3 species of Lactobacillus. A method for permeabilization of cells was developed using toluene and ethanol combined with mechanical treatment. It was found that the AT activities in the washed permeabilized cells (W-PC) corresponded well with those in cell-free extracts (CFE). The AT specificity pattern was both species and strain dependent. Strains of L. helveticus had high specificity for aromatic amino acids (ArAA) and lower activity against branched-chain amino acids (BcAA) and Asp, while strains of L. paracasei subsp. paracasei degraded BcAA and Asp, but had a lower and variable specificity against ArAA. 1 of the L. paracasei strains was characterized as having very high AT activity against all 3 BcAA (Ile, Leu, Val) compared with the other L. paracasei strains tested. Strains of L. danicus, which is a newly discovered Lactobacillus species isolated from cheese, had up to approx. 20x higher AT activity against Leu than L. paracasei and L. helveticus. The permeabilized cells of L. danicus also had considerably higher AT activity against ArAA than L. paracasei and L. helveticus strains, as well as 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.