Table 1

CYP3A content and MDZ hydroxylation activity in human duodenum and jejunum

Microsomal CYP3A (pmol/mg of protein)41.3  ± 30.539.7  ± 31.2
Microsomal intrinsic clearance (μl/min/mg of protein)133.8  ± 109.1118.3  ± 98.2
Homogenate CYP3A (pmol/mg of protein)9.2  ± 6.28.4  ± 5.4
Mucosal CYP3A (nmol/g of mucosa)0.89  ± 0.580.91  ± 0.61
Mucosal intrinsic clearance (ml/min/g of mucosa)3.83  ± 3.623.67  ± 3.81

Total homogenate and microsomes were prepared from mucosal scrapings of paired human duodenum and jejunum from eight different donors. Protein concentration and specific CYP3A content for each tissue fraction was measured as described in Experimental Procedures. Two of eight preparations contained relatively low amounts of CYP3A5 in addition to CYP3A4, which were resolved from one another by SDS-polyacrylamide gel electrophoresis. Microsomes were incubated with varying concentrations of MDZ for determination of Km andV max parameters for 1′-hydroxylation. The microsomal intrinsic formation clearance was calculated as the ratio ofV max to Km . The mucosal intrinsic formation clearance was calculated from the product of microsomal intrinsic clearance and an experimentally determined concentration of microsomal protein in the total mucosal mass (see text).