Intestine quantitative aspects

Quantitative Aspects of Intestinal Enzymes How Much and How Active . 12... 

Similar problems have compUcated the quantitation of HMG-CoA reductase activity as a measure of the rate of cholesterol synthesis. For example, it has not been established as firmly for the intestine as for the hver that this enzyme is rate limiting to the overall synthesis of the cholesterol molecule [23]. Furthermore, HMG-CoA reductase in both the intestine and liver is subject to a phosphorylation-dephosphorylation reaction that modifies enzyme activity and is involved in the activation of an inactive (phosphorylated) to an active (dephos-phorylated) form during homogenization of the mucosa [24,25]. Finally, HMG-CoA reductase is incompletely recovered from the mucosa during preparation of micro-somes [26,27] and is very sensitive to inactivation by proteases present in the intestine [28]. These various technical problems have led to considerable confusion with respect to various aspects of intestinal cholesterol synthesis and have made it difficult to interpret quantitatively some of the results presented below. 

The above experiments indicate that the intestinal microflora is an important variable in qualitative and quantitative bile acid metabolism. In the following sections, some specific aspects of this interaction will be examined in detail. 

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