Cholesterol and vitamin

Elimination usually involves loss of a proton together with a nucleophilic group such as -OH, -NH3+, phosphate, or pyrophosphate. However, as in Eq. 13-18, step c, electrophilic groups such as -COO-can replace the proton. Another example is the conversion of mevalonic acid-5-pyrophosphate to isopentenyl pyrophosphate (Eq. 13-19) This is a key reaction in the biosynthesis of isoprenoid compounds such as cholesterol and vitamin A (Chapter 22). The phosphate ester formed in step a is a probable intermediate and the reaction probably involves a carbo-cationic intermediate generated by the loss of phosphate prior to the decarboxylation. 

EXPERIMENT 11 Measurement of Cholesterol and Vitamin C in Biological Samples 371... 

Shibata H, Kumagai S, Watanabe S, Suzuki T. Relationship of serum cholesterols and vitamin E to depressive status in the elderly. J Epidemiol 1999 9 261-267. 

It has been shown that there is a statistically significant correlation between the serum calcium and cholesterol levels in idiopathic hypercalcemia of infancy (F7). At the same time it is recognized that a cholesterol derivative, 7-dehydrocholesterol, is a precursor of vitamin D3. In view of the clear association between hypercalcemia and hypercholesterolemia in idiopathic hypercalcemia, and in view of the possible relationship between cholesterol and vitamin D, Forfar et al. (F7) have suggested that idiopathic hypercalcemia may be due to a disorder of cholesterol metabolism, in which an excess of vitamin D-like substance is produced. They further postulate that this substance, although hyper-... 

Rosen, H., Reshef, A., Maeda, N., Lippoldt, A., Shpizen, S., Triger, L., Eggertsen, G., Bjorkhem, I., Leitersdorf, E. 1998. Markedly reduced bile acid synthesis but maintained levels of cholesterol and vitamin D metabolites in mice with disrupted sterol 27-hydroxylase gene. J. Biol. Chem. 273 14805-14812. 

S. Shpizen, L. Triger et al. (1998). Markedly reduced bile acid synthesis but maintained levels of cholesterol and vitamin D metabolites in mice with disrupted sterol 27-hydroxylase gene. 

McIntosh, G. H., F. H. Bulman, R. J. Illman, and D. L. Topping. 1984. The influence of age, dietary cholesterol and vitamin C deficiency on plasma cholesterol concentration in the marmoset. Nutrition Reports International 29 673-682. 

Sugar residues, belonging to glycoproteins or glycolipids, are also present at the outer surfaces of cell membranes, as well as cholesterol and vitamin E. Biomembranes usually contain carbon chains of differing lengths, moreover opposite surfaces have somewhat different compositions and bio layers are asymmetric. (Biomembranes do not in reality correspond to the idealised representations which are often nsed e.g. Figures 11.6 and 11.7.)... 

As with prokaryotic P450s, active site diversity underlies the unique roles of P450s in mamma-han physiology. Structures now are available for several of the enzymes that hydroxylate the aliphatie side chains of cholesterol and vitamin D3. P450 llAl eatalyzes three successive oxy-... 

The hydrolysis of ethyl butyrate is a ubiquitous phenomenon occurring in animal and plant tissues of many types. The enzyme responsible for the catalysis of this hydrolysis has been purified. In general, tissues contain one or more aliphatic esterases (or ali-esterases O which have a broad specificity for simple esters, possibly extending to esters of cholesterol and vitamin A. 

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