Fluorescence behaviour of 5,10-methenyltetrahydrofolate, 10-formyltetrahydrofolate, 10-formyldihydrofolate, and 10-formylfolate in aqueous solution at pH 8

5-Methyltetrahydrofolate Is a Crucial Factor in Determining the Bioaccessibility of Folate in Bread

This study investigated the bioaccessibility of folate in wheat bread baked with different ingredients and processing methods. Next, different matrices were spiked with 5-methyltetrahydrofolate, gallic acid (GA), or both to investigate the stability of 5-methyltetrahydrofolate during in vitro digestion. The folate bioaccessibility in bread varied from 44 to 96%. The inclusion of whole-grain or faba bean flour significantly improved both folate content and bioaccessibility. Baking with yeast increased the folate content by 145% in bread but decreased folate bioaccessibility compared to the bread without added yeast because of the instability of 5-methyltetrahydrofolate. Spiking experiments confirmed oxidation as a critical reason for 5-methyltetrahydrofolate loss during digestion. However, GA protected this vitamer from degradation. Additionally, 5-methyltetrahydrofolate was less stable in whole-grain wheat matrices than other matrices. This study demonstrated that the stability of 5-methyltetrahydrofolate is crucial for folate bioaccessibility in bread, and methods for stabilizing this vitamer should be further studied.

Flavin Adenine Dinucleotide and N5 ,N10 -Methenyltetrahydrofolate are the in planta Cofactors of Arabidopsis thaliana Cryptochrome 3

Members of the cryptochrome/photolyase family (CPF) of proteins utilize noncovalently bound light-absorbing cofactors for their biological function. Usually, the identity of these cofactors is determined after expression in heterologous systems leaving the question unanswered whether these cofactors are identical to the indigenous ones. Here, cryptochrome 3 from Arabidopsis thaliana was expressed as a fusion with the green fluorescent protein in Arabidopsis plants. Besides the confirmation of the earlier report of its localization in chloroplasts, our data indicate that fractions of the fusion protein are present in the stroma and associated with thylakoids, respectively. Furthermore, it is shown that the fusion protein expressed in planta contains the same cofactors as the His₆ -tagged protein expressed in Escherichia coli, that is, flavin adenine dinucleotide and N⁵ ,N¹⁰ -methenyltetrahydrofolate. This demonstrates that the heterologously expressed cryptochrome 3, characterized in a number of previous studies, is a valid surrogate of the corresponding protein expressed in plants. To our knowledge, this is also a first conclusive analysis of cofactors bound to an Arabidopsis protein belonging to the CPF and purified from plant tissue.

Fungal cryptochrome with DNA repair activity reveals an early stage in cryptochrome evolution

DASH (Drosophila, Arabidopsis, Synechocystis, Human)-type cryptochromes (cry-DASH) belong to a family of flavoproteins acting as repair enzymes for UV-B-induced DNA lesions (photolyases) or as UV-A/blue light photoreceptors (cryptochromes). They are present in plants, bacteria, various vertebrates, and fungi and were originally considered as sensory photoreceptors because of their incapability to repair cyclobutane pyrimidine dimer (CPD) lesions in duplex DNA. However, cry-DASH can repair CPDs in single-stranded DNA, but their role in DNA repair in vivo remains to be clarified. The genome of the fungus Phycomyces blakesleeanus contains a single gene for a protein of the cryptochrome/photolyase family (CPF) encoding a cry-DASH, cryA, despite its ability to photoreactivate. Here, we show that cryA expression is induced by blue light in a Mad complex-dependent manner. Moreover, we demonstrate that CryA is capable of binding flavin (FAD) and methenyltetrahydrofolate (MTHF), fully complements the Escherichia coli photolyase mutant and repairs in vitro CPD lesions in single-stranded and double-stranded DNA with the same efficiency. These results support a role for Phycomyces cry-DASH as a photolyase and suggest a similar role for cry-DASH in mucoromycotina fungi.

Fluorescence of bioaerosols: mathematical model including primary fluorescing and absorbing molecules in bacteria

This paper describes a mathematical model of fluorescent biological particles composed of bacteria, viruses, or proteins. The fluorescent and/or light absorbing molecules included in the model are amino acids (tryptophan, etc.); nucleic acids (DNA, RNA, etc.); coenzymes (nicotinamide adenine dinucleotides, flavins, and vitamins B₆ and K and variants of these); and dipicolinates. The concentrations, absorptivities, and fluorescence quantum yields are estimated from the literature, often with large uncertainties. The bioparticles in the model are spherical and homogeneous. Calculated fluorescence cross sections for particles excited at 266, 280, and 355 nm are compared with measured values from the literature for several bacteria, bacterial spores and albumins. The calculated 266- and 280-nm excited fluorescence is within a factor of 3.2 of the measurements for the vegetative cells and proteins, but overestimates the fluorescence of spores by a factor of 10 or more. This is the first reported modeling of the fluorescence of bioaerosols in which the primary fluorophores and absorbing molecules are included.

Emission properties of dihydropterins in aqueous solutions

Pterins belong to a class of heterocyclic compounds present in a wide range of living systems and accumulate in the skin of patients affected by vitiligo, a depigmentation disorder. The study of the emission of 7,8-dihydropterins is difficult because these compounds are more or less unstable in the presence of O(2) and their solutions are contaminated with oxidized pterins which have much higher fluorescence quantum yields (Φ(F)). In this work, the emission properties of six compounds of the dihydropterin family (6-formyl-7,8-dihydropterin (H(2)Fop), sepiapterin (Sep), 7,8-dihydrobiopterin (H(2)Bip), 7,8-dihydroneopterin (H(2)Nep), 6-hydroxymethyl-7,8-dihydropterin (H(2)Hmp), and 6-methyl-7,8-dihydropterin (H(2)Mep)) have been studied in aqueous solution. The fluorescence characteristics (spectra, Φ(F), lifetimes (τ(F))) of the neutral form of these compounds have been investigated using the single-photon-counting technique. Φ(F) and τ(F) values obtained lie in the ranges 3-9 × 10(-3) and 0.18-0.34 ns, respectively. The results are compared to those previously reported for oxidized pterins.