Thoughts
I think the most important statement in this paper is de novo biosynthesis is not found in animals. That means we must acquire it from the animals who eat these things, the plants/ fungi themselves, and/ or have the right bacteria (prokaryote) strains. The plants need to have functioning mitochondria and sources of bioavailable Fe and S for thiamine’s synthesis.
Notes
Vitamin B1, in the form of thiamin diphosphate (TPP), acts as a cofactor for several enzymes in key cellular metabolic path- ways such as glycolysis, the pentose phosphate pathway and the citric acid cycle (TCA), in addition to amino acid and nonmeval- onate isoprenoid biosynthesis, respectively (1). More recently, it has been implicated in tolerance to DNA damage (2) and as an activator of disease resistance in plants (3, 4). It is an essential compound in all-living systems, but de novo biosynthesis is only found in pro- karyotes, fungi, and plants; therefore, animals must acquire it from dietary sources.
proteins involved in thiamin biosynthesis in plants have been reported to have differential subcellular localizations. For example, THI1 involved in the syn- thesis of the thiazole moiety, is targeted to both mitochondria and plastids (24), whereas the recently described thiamin pyrophos- phokinase is reported to be cytosolic (25). To assemble the site(s) of synthesis of the thiamin molecule, it is thus of interest to know the subcellular localization of THIC [Fe-S containing protein].
Vitamin B1 was discovered in 1932, its structure was elucidated in 1936, and it was the first such compound to be recognized as an essential metabolic cofactor. Yet, surprisingly many facets of its metabolism still remain unresolved. Nowhere is this more apparent than in plants. In this study, we show that THIC plays an essential role in the synthesis of vitamin B1 and moreover is necessary for plant viability. The presence of a Fe-S cluster in THIC suggests that it must be coupled with a reductant to enable catalytic activity. In bacteria, this can be accomplished by the flavodoxin/flavodoxin reduc- tase/NADPH system as for the non-mevalonate isoprenoid biosynthesis proteins, IspG and IspH (37). However, flavodoxin is absent from the plastids of phototrophic organisms, but reduction could be achieved by ferredoxin, which can supply the electrons either in the presence of light or in the dark via ferrredoxin-NADP reductase and NADPH (38). In plants, many chloroplastic enzymes are also activated and deactivated through oxidation/reduction reactions via the thioredoxin sys- tem. THIC has been found as a potential thioredoxin target protein in chloroplasts (39) and could influence the protein at several levels, including activity, oxidative regulation, and as- sembly or folding (40). Thus, the regulation of thiamin biosynthesis in plants may occur at several levels, i.e., riboswitch and redox.
Kathleen Stewart 