Pyridoxal biochemical function

The fundamental biochemical function of pyridoxal-5 -phosphate is the formation of aldimines with a-amino acids that stabilize the development of carbanionic character at the a and /3 carbons of a-amino acids in intermediates, such as those in figures 10.4b and c. Enzymes acting alone cannot stabilize these carbanions and so cannot, by themselves, catalyze reactions requiring their formation as intermediates. 

A Saturation of Biochemical Function. A reliable biochemical indicator is required. For niacin, which NAD" - or NADP -containing enzyme should be selected Which transaminase will be the indicator for pyridox-ine Which function of vitamin A should be j selected for retinol, vision in the rods or cell differentiation As noted from Table 8.2, many of the assays for vitamin status have significant limitations to estimate reliable doses. 

Biochemical functions pyridoxal phosphate is essential for aminotransferase (transamination) reactions in amino aoid metabolism and so is needed both for biosynthesis of the non-essential amino acids and also for amino acid oxidation for energy metabolism. Also an Important component of glycogen phosphorylase... 

A review by Rase . summarizes. studies on the effects of certain hormones on vitamin B(, nutrition in humans, on the biochemical interrelationship between steroid hormones and pyridoxal phasphate-dependent enzymes, and on the role of vitamin B(, in regulating hypothalamus-pituitary functions. Some of these studies have important clinical implications. The use of estrogen-containing oral contraceptives has been investigated as a factor leading to an abnormality of tiyptophan metaboli.sm. This abnormality resembles dietary vitamin B deficiency and responds favorably to treatment with the vitamin. For some time, there has been clinical interest in the relationship between certain hormones and vitamin B function because abnormal urinary excretion of tiyptophan metabolites was observed during pregnancy and in patients with hyperthyroidism. 

Many of the biochemical reactions of amino acids require pyridoxal 5 -phosphate (PLP), the active form of vitamin 65, as a coenzyme. Before acting on an amino acid, PLP uses its aldehyde function to form an imine with file amino group of a lysine side chain of a protein. 

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