Steroids, Hormones and Enzymes

This unit brings together some of the basic chemistry looked at in earlier chapters and applies it to some important biochemical molecules  

Try this short test. If you score more than 80 % you can use the chapter as a revision of your knowledge. If you score less than 80 %you probably need to work through the text and test yourself again at the end using the same test. If you still score less than 80 % then come back to the chapter after a few days and read again. 

Chemistry An Introduction for Medical and Health Sciences, A. Jones 2005 John Wiley Sons, Ltd 

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Steroid hormones and thyroid hormone carry out their effects by way of gene activation. In contrast to the protein/peptide hormones, which alter existing enzyme activity, these hormones induce the synthesis of new enzymes that then influence cellular metabolism. 

The cytochrome P450 (CYP450) enzyme superfamily is the primary phase I enzyme system involved in the oxidative metabolism of drugs and other chemicals. These enzymes also are responsible for all or part of the metabolism and synthesis of a number of endogenous compounds, such as steroid hormones and prostaglandins. 

Whether /3-glucuronidase in the organs of the cat would respond to treatment with steroid hormones and other agents in the same fashion as in other species9 is another interesting problem that arises from these experiments the enzyme in cat tissues shows the variation in activity with age (see Table I, d) first observed in mice,112 and a striking elevation in enzyme activity in cat sciatic nerve is seen after injury to the nerve.86... 

As discussed in Section 9.3.3, pyridoxal phosphate is involved in the regulation of gene expression, terminating the responses to steroid hormones and inactivating some tissue-specific transcription factors. There is decreased synthesis of pancreatic digestive enzymes in vitamin Bg deficiency, although the synthesis of other pancreatic proteins is unaffected (Dubick et al., 1995). 

The cytochrome P-450 monooxygenase.s are located in the endoplasmic reticulum, a highly organized and complex network of intracellular membranes that is particularly abundant in tissues such as the liver. When the.se tissues are dismpted by homogenization, the endoplasmic reticulum loses its structure and is converted into small vesicular bodies known as mkrosames. Mitochondria hou.se many of the cytochrome enzymes that are responsible for the biosynthesis of steroidal hormones and metabolism of certain vitamins. 

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. 

JR Gillette. Insights into deuterium isotope effects on the metabolism of steroid hormones and foreign compounds by cytochrome P-450 enzymes. Life Sci 49 1-14, 1991. 

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