3-Hydroxy-3-methylglutaryl coenzyme A reductase in isolated villous and crypt cells of the rat ileum

The localization of 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMG-CoA reductase) in the villous and crypt cells of the small intestine was accomplished after separating these cells from the mucosal layer by sequential dissociation in a 'dual-buffer', system. Consistent separation was demonstrated by using the marker enzymes alkaline phosphatase, specific to the villous cell, and thymidine kinase, specific to the crypt cell. Cells obtained were 95-100% viable, and no relative difference in lability was observed, as evidenced by the equal distribution of acid phosphatase. This method of cell separation is an improvement over the 'scraping' technique which damages cells severely and produces villous preparations which contain little or no reductase activity. The HMG-CoA reductase specific activity in whole cell homogenates of the ileal villi was 0.47 and of the crypts was 0.27 nmol/min per mg of protein, considerably higher values than reported earlier. Also in comparison to the crypts, the villi incorporated 1.5-fold more [¹⁴C]acetate into sterols, a ratio similar to that describing the distribution of HMG-CoA reductase in the two cell populations. These results unequivocally establish that the villi have higher HMG-CoA reductase activity than the crypts and confirm earlier reports that the villi are a major site of sterol synthesis. The sterol biosynthetic capacity of the small intestine was highest in the ileum and decreased towards the jejunum. The HMG-CoA reductase specific activity of the ileum averaged 0.30 and that of the jejunum 0.10 nmol/min per mg of protein; however, the cholesterol content of the ileum was slightly lower than the jejunum.