cjm
Member
We found the thiaminase I enzyme from Clostridium botulinum efficiently degrades thiamine in the presence of pyridoxine (vitamin B6) as a co-substrate but has relatively limited activity in the presence of nicotinic acid (vitamin B3).
"Pyridoxine yielded 60.6% degradation, nicotinic acid yielded 42.5% degradation, and folic acid yielded 16.9% under the same conditions. A small amount of degradation of thiamine was observed in the presence of L-methionine (8.0%) and L-histidine (10.1%). None of the other L-amino acids or vitamins yielded significant degradation of thiamine in the presence of thiaminase, suggesting the presence of dietary pyridoxine or nicotinic acid was required for thiaminase activity."
These co-substrate limitations and the common presence of inhibitory dietary factors complement recent studies reporting that the intended function of thiaminase enzymes is to recycle thiamine breakdown products for thiamine synthesis, not thiamine degradation.
It's not us (humans), it's them (the bacteria):
"some microorganisms preferentially use precursors for thiamine synthesis, and are incapable of uptake of exogenous intact thiamine²³,⁸⁷"
"may favor certain bacteria... an inhibitory compound to competitors... some degradation products of thiamine are toxic analogues that inhibit enzymatic reactions for which thiamine is a required cofactor⁷⁸,⁷⁹,⁸⁰,⁸¹,⁸²,"
Nice share. This study was recent, too -- April 2023.