Pyridoxal, pyridoxol and pyridoxamine

In mammals, dietary vitamin forms, including pyridoxal, pyridoxol, and pyridoxamine, can all be converted to the respective coenzyme forms by phosphorylation. 

Prokaryotic organisms synthesise a primary form of vitamin pyridoxol 5 -phosphate from 1-deoxy-D-xylulose 5-phosphate (l-deoxy-D-t/treo-pent-2-ulose 5-phosphate) and 2-amino-2-deoxy-D-threo-tetronic (2-amino-2-deoxy-D-threonic) acid, known as 4-(phosphohydroxy)-L-threonine or 4-hydroxy-i-threonine 4-phosphate. Phosphohydroxythreonine arises from D-erythrose 4-phosphate, a product of decomposition of D-fructose 6-phosphate. Non-phosphorylated forms (pyridoxal, pyridoxol and pyridoxamine) are produced by hydrolysis of the corresponding phosphates. Animals do not synthesise vitamin Bg de novo, only convert the non-phosphorylated forms in the Hver, erythrocytes, and other tissues into the corresponding phosphates and the individual forms of each other. Pyridoxal 5 -phosphate arises by oxidation of pyridoxol 5Lphosphate and transamination of pyridoxal 5 -phosphate provides pyridoxamine 5Lphosphate. Both these forms of vitamin Bg are catalytically active. Pyridoxal 5 -phosphate... 

Williams, A.K. and Cole, P.D., Vitamin Be ion exchange chromatography of pyridoxal, pyridoxol and pyridoxamine, J. Agric. Food Chem., 2i, 915-916, 1975. 

Vitamin B Three substances are classed under the term pyridoxine or adermine pyridoxol, pyridoxal and pyridoxamine. Pyridoxine was isolated by various study groups in 1938. Its structure was described by Folkers and Kuhn in 1939. Pyridoxal and pyridoxamine were discovered by Snell in 1942. Pyridoxal phosphate and pyridoxamine phosphate are biologically active substances. Intestinal absorption of Bg is dose-dependent and not limited. In alcoholism, a deficiency of vitamin Bg is encountered in 20—30% of cases, whereas the respective percentage is 50—70% in alcoholic cirrhosis. Vitamin Bg is an important coenzyme for transaminases, which transfer amino groups from amino adds to keto acids. In this way, biochemical pathways between the dtiic acid cycle and carbohydrate and amino acid metabolisms are created. (104)... 

Pyridoxine is available from whole-grain cereals, peanuts, eom. meat, poultry, and fish. Up to 40% of the vitamin may be destroyed, however, during cooking. Food sources contain all three forms, cither in their free form or phosphory-lated. Plants contain primarily pyridoxol and pyridoxamine, while animal sources provide chiefly pyridoxal. Many plants also contain a glycoside of pyridoxol. which is included in vitamin content determinations. Although this conjugate is absorbed, it is not used well. This may explain the lower bioavailability of the vitamin from plant sources than from animal sources. 

The term vitamin Bg refers to a group of naturally occurring pyridine derivatives represented by pyridoxine (pyridoxol, PN), pyridoxal (PL), and pyridoxamine (PM), and their phosphorylated derivatives. They are collectively referred to as vitamin Bg vitamers. The natural free forms of the vitamers could be converted to the key coenzymatic form, pyridoxal phosphate (PLP), by the action of two enzymes, a kinase and an oxidase. There are more than 140 PLP-dependent enzymatic reactions, and they are distributed in all organisms. These enzymes comprise diverse groups such as the oxidoreductases, transferases, hydrolases, lyases, and isomerases. About... 

Metabolites that contain pyridoxol (2-methyl-3-hydroxy-4,5-di[hydroxymethyl]pyridine), the water-soluble vitamin B6. Phosphorylated forms of pyridoxal (the aldehyde form) and pyridoxamine (the amino form), known respectively as pyridoxal 5-phosphate (PLP) and pyridoxamine 5-phosphate (PMP), are tightly-bound coenzymes. 

The generic descriptor vitamin Be includes six vitamers the alcohol pyridox-ine, the aldehyde pyridoxal, the amine pyridoxamine, and their 5 -phosphates. There is some confusion in the older literature, because at one timepyridoxine was used as a generic descriptor, with pyridoxol as the specific name for the alcohol. As shown in Figure 9.1, the vitamers are metabolicaUy interconvertible and, as far as is known, they have equal biological activity. 

The vitamin Bg group comprises three natural forms pyridoxine (pyridoxol) (PA/), pyridoxamine (PM), and pyridoxal (PL), which are 4-substituted 2-methyl-3-hydroxyl-5-hydroxymethyl pyridines (Figure 30-13). During metabolic conversions, each vitamer becomes phosphorylated at the 5-hydroxymethyl substituent. Although both pyridox-amine-5 -phosphate (PMP) and pyridoxal-S -phosphate (PLP, P-5 -P) interconvert as coenzyme forms during aminotransferase (transaminase)-catalyzed reactions, PLP is the coenzyme form that participates in the large number of Bg-dependent enzyme reactions. 

Pyridoxol 210 (pyridoxine, 3-hydroxy-4,5-bis(hydroxymethyl)-2-methylpyridine, vitamin B6) was formerly known as adermine (Kuhn 1938) because vitamin B5 deficiency causes skin diseases in animals. Pyridoxal (211, R = CHO) and pyridoxamine (211, R = CH2NH2) also belong to the vitamin B group. Pyridoxal phosphate 212 is a coenzyme for many of the enzymes involved in the metabolism of amino acids. Nicotinamide adenine dinucleotide 213 (NAD , reduced form NADH) is a component of oxidoreductases (for its action see p 293, synthesis see p 131). 

Vitamin Bg (pyridoxine also known as pyridoxol, 118) is an essential growth factor in the diet of many organisms and animals. It forms part of a coenzyme (pyridoxylphosphate) and it is a cofactor for a class of enzymes known as transaminases. A transaminase or an aminotransferase is an enzyme that catalyzes a type of reaction between an amino acid and an a-keto acid. The presence of elevated transaminase levels can be an indicator of liver damage. Vitamin Bg has both an aldehyde form (pyridoxal, 119) and an amine form (pyridoxamine, 120), and it is known that pyridoxal phosphate is a carrier of amino groups and sometimes amino acids. ... 

Vitamin B6 activity is exhibited by pyridoxine (Formula 6.11) or pyridoxol (R = CH2OH), pyridoxal (R = CHO) and pyridoxamine (R = CH2NH2). The metabolically active form. 

The dominant forms in animal tissues are pyridoxal 5 -phosphate and pyridoxamine 5 -phosphate. An important metabolite of pyridoxal excreted in the urine is biologically inactive 4-pyridoxic acid (5-77) and its lactone, which is called 4-pyridoxolactone (5-78). Minor metaboHtes generated by oxidation in position C-5 are isopyridoxal (aldehyde), the corresponding carboxylic acid and its lactone. Pyridoxol 5 -phosphate is the dominant form in plant tissues. 

Vitamin Bg is relatively stable in acidic solutions, and less stable in neutral and alkaline solutions, particularly in the light. Pyridoxol is more stable than pyridoxal and pyridoxamine. 

Raw meat contains pyridoxal phosphate as the main vitamin form, whereas cooked meat predominantly contains a product of its transamination pyridoxamine phosphate. For example, the main form of vitamin Bg in raw chicken meat is pyridoxal phosphate (56%), followed by pyridoxamine phosphate (42%) and pyridoxamine (2%). The main form in roasted chicken meat is pyridoxamine phosphate (70%), followed by pyridoxal phosphate (21%), pyridoxol (7%) and pyridoxamine (2%). Vitamin retention in roasted meat is about 45-65%. 

Vitamin Bg is a mixture of six interrelated forms pyridoxine (or pyridoxol) (Figure 19.23), pyri-doxal, pyridoxamine, and their 5 -phosphates derivatives. Interconversion is possible between all forms. The active form of the vitamin is pyridoxal phosphate, which is a coenzyme correlated with the function of more than 60 enzymes involved in transamination, deamination, decarboxylation, or desulfuration reactions. 

Pyridoxine (pyridoxol), pyridoxamine, and pyridoxal are the three natural forms of vitamin Bg. They are converted to pyridoxal phosphate, which is required for the synthesis, catabohsm, and interconversion of amino acids. 

Nomenclature. Pyridoxine (vitamin Bg) group name for pyridoxine (pyridoxol), pyridoxal, pyridoxamine and the 5 -phosphorylated derivatives of these compounds. 

Six vitamers of Be, having equivalent biopotency, are found in nature [1,16] pyridoxine or pyridoxol, pyridoxal, pyridoxamine, and their 5 -phosphate esters acid pyridoxic and pyridoxine-glucoside are inactive forms occurring in plant tissues. Regulation 1925/2006/EC cites... 

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