The Role of Pyridoxal Phosphate in Steroid Hormone Action and Gene Expression

3 The Role of Pyridoxal Phosphate in Steroid Hormone Action and Gene Expression 

Steroid hormones act by binding to, and activating, nuclear receptors that then bind to hormone response elements on DNA, increasing (or sometimes decreasing) the transcription of specific genes. 

Gross clinical deficiency of vitamin Be is extremely rare. The vitamin is widely distributed in foods (although a significant proportion in plant foods may be biologically unavailable Section 9.1), and intestinal flora synthesize relatively large amounts, at least some of which may be absorbed and hence available. 

A variety of studies have shown that 10% to 20% of the population of developed countries have marginal or inadequate stams, as assessed by erythrocyte transaminase activation coefficient (Section 9.5.36) or plasma pyridoxal phosphate (Section 9.5.1 Bender, 1989b). This may be sufficient to enhance the responsiveness of target tissues to steroid hormones (Section 9.3.3), and may be important in the induction and subsequent development of hormone-dependent cancer of the breast and prostate. Vitamin Be supplementation may be a useful adjunct to other therapy in these common cancers certainly, there is evidence that poor vitamin Be nutritional stams is associated with a poor prognosis in women with breast cancer. 

In vitamin Be-deflcient experimental animals, there are skin lesions (e.g., acrodynia in the rat) and fissures or ulceration at the corners of the mouth and over the tongue, as well as a number of endocrine abnormalities defects in the metabolism of tryptophan (Section 9.5.4), methionine (Section 9.5.5), and other amino acids hypochromic microcytic anemia (the first step of heme biosynthesis is pyridoxal phosphate dependent) changes in leukocyte count and activity a tendency to epileptiform convulsions and peripheral nervous system damage resulting in ataxia and sensory neuropathy. There is also impairment of immune responses, as a result of reduced activity of serine hydroxymethyltransferase and hence reduced availability of one-carbon substituted folate for nucleic acid synthesis (Section 10.3.3). It has been suggested 

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