Pyridoxine structural specificity

Observations on the activity of pyridoxin mid closely related compounds with a variety of different types of organism are collected in Table XI. The results show the high biological specificity of the pyridoxin structure... 

A second clue to the catalytic mechanism of phosphorylase is its requirement for pyridoxal phosphate (PLP), a derivative of pyridoxine (vitamin B5, Section 8.6.1). The aldehyde group of this coenzyme forms a Schiff base with a specific lysine side chain of the enzyme (Figure 21.7). The results of structural studies indicate that the reacting... 

Lack or deficiency of a V., as a result of unbalanced nutrition, leads to charaeteristic metabolic disturbances. Complete absenee of a V. leads to avitaminosis, with typical clinical symptoms. Relative deficiency of a V. causes hypovitaminosis. Such conditions are reversible by administration of the appropriate V. Excessive intake of certain V, e.g. V.A or V.D, can lead to hypervitaminosis. Formerly, V. were named after the diseases they cured, e.g. antiscorbutic V., antirachitic V, antiberiberi factor. Not all V., however, have such a pronounced specificity, and the clinical pictures of many avitaminoses and hypovitaminoses are complex and variable. A nomenclature based on letters of the alphabet was developed simultaneously the designations A, B, C, D and E were applied in the historical order of discovery. Subscripts were applied as more refined chemical analysis revealed that the originally isolated substances were in fact complex mixtures. This was especially true for the B vitamins. Partly because of confusion over the B complex , trivial names which give an indication of the chemical structure of the V. (e.g. pyridoxine or pyiidoxol for V.B() are now preferred. 

Pyridoxine, the parent substance of pyridoxal phosphate, is also known as vitamin Be (page 165). Many coenzymes contain a derivative of one or other of the B vitamins as an essential part of their structure. Coenzymes may react with a number of different enzymes which are specific for different substrates but which catalyse the same general type of reaction. 

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