Liver kinetic aspects

Many enzymes have been reported which catalyze the hydrolysis of other amino acid amides 2Jfi). These enzyme systems have not been investigated systematically and, at present, it is not possible to determine whether they are different from the peptidases. Some kinetic aspects of the hydrolysis of n-hexamide, a typical substrate for the nonspecific amidase of rabbit liver, have been studied by Bray et al. (272). 

Figure 4. The Zn model expanded to illustrate the compartments used to analyze the process of zinc absorption. Compartment 16 represents stomach and 17-25 represent the intestine as a set of compartments connected in series with outputs to red blood cells, plasma, and liver. The model allows the definition of absorption as a kinetic process and the separate consideration of various aspects of this process. The model then could be used to define the kinetics, not only of total zinc absorption, but also of zinc entry directly from the gut into plasma, entry into plasma following uptake by liver and red blood cells, and absorption rates at various times after administration.

The transporter has much lower activity in kidney [66], but the kinetic patterns are similar to those observed with liver mitochondria. Prevention of glutamate efflux from mitochondria by H" in kidney tubular cells is probably a very important aspect of control of ammoniagenesis in kidney (c.f.. Section 6.4). 

The compartmental model of /8-carotene metabolism presented here is compatible with previously developed compartmental models of retinol metabolism (Green et aL, 1985 Lewis et aL, 1990). For example, the compartmental model of the dynamics of /S-carotene metabolism features two kinetically distinct pools of retinol in the liver, recycling of plasma retinol by liver, and irreversible loss of retinol from the plasma. These aspects of retinol metabolism (predicted by the compaitmental model) are compatible with already described aspects of retinol metabolism. 

---