Pyridine nucleotide Pyridoxal phosphat

Tissue also contains some endogenous species that exhibit fluorescence, such as aromatic amino acids present in proteins (phenylalanine, tyrosine, and tryptophan), pyridine nucleotide enzyme cofactors (e.g., oxidized nicotinamide adenine dinucleotide, NADH pyridoxal phosphate flavin adenine dinucleotide, FAD), and cross-links between the collagen and the elastin in extracellular matrix.100 These typically possess excitation maxima in the ultraviolet, short natural lifetimes, and low quantum yields (see Table 10.1 for examples), but their characteristics strongly depend on whether they are bound to proteins. Excitation of these molecules would elicit background emission that would contaminate the emission due to implanted sensors, resulting in baseline offsets or even major spectral shifts in extreme cases therefore, it is necessary to carefully select fluorophores for implants. It is also noteworthy that the lifetimes are fairly short, such that use of longer lifetime emitters in sensors would allow lifetime-resolved measurements to extract sensor emission from overriding tissue fluorescence. 

Thiol enzyme. SH-enzyme an enzyme whose activity depends on the presence of a certain number of free tUol groups. T.e. are found among the hydrolases, oxidoreductases and transferases. Known T.e. are bromelain, papain, urease, various flavoenzymes, pyridine nucleotide enzymes, pyridoxal phosphate enzymes and thiolproteinases. T.e. are t ically inhibited by Sulfhydryl reagents (see). 

Nicotinic acid and riboflavin, the precursors of the pyridine and flavin nucleotides and ubiquinone or coenzyme Q, are essential components of the electron-transport chain. Pyridoxine, the precursor of pyridoxal phosphate, is essential for the activity of transaminases and amino acid decarboxylases and, therefore, for gluconeogenesis and for the production of biogenic amines. 

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