The maximum pore fluid pressures due to uniaxial compression are determined for both the vascular porosity (Haversian and Volkmann's canals) and the lacunar-canalicular porosity of live cortical bone. It is estimated that the peak pore water pressure will be 19 percent of the applied axial stress in the vascular porosity and 12 percent of the applied axial stress in the lacunar-canalicular porosity for an impulsive step loading. However, the estimated relaxation time for the vascular porosity (1.36 microseconds) is three orders of magnitude faster than that estimated for the lacunar-canalicular porosity (4.9 ms). Thus, under physiological loading, which has a stress rise time generally larger than 1 ms, pressures higher than the vascular pressure cannot be sustained in the vascular porosity due to the swift pressure relaxation in this porosity (unless the fluid drainage through the boundary is obstructed). The model also predicts a slight hydraulic stiffening of the bulk modulus due to longer draining time of the lacunar-canalicular porosity. The undrained bulk modulus is 6 percent higher than the drained bulk modulus in this case.

T h e enzymes of mitochondrial /3-oxidation are thought to be organized in at least two functional complexes, a membrane-bound, long-chainspecific P-oxidation system and a matrix system consisting of soluble enzymes with preferences for medium-chain and short-chain substrates. This hypothesis is supported by the observation that the inactivation of long-chain 3-ketoacyl-CoA thiolase by 4-bromotiglic acid (4-bromo-2-methylbut-2-enoic acid) causes the complete inhibition of palmitate P-oxidation even though 3-ketoacylCoA thiolase, which acts on 3-ketopalmitoyl-CoA, remains partly active. T h e observed substrate specificities of long-chain acyl-CoA dehydrogenase (LCAD) and very-long-chain acyl-CoA dehydrogenase prompt the suggestion that LCAD is a functional component of the long-chainspecific /3-oxidation system. Altogether, a view is emerging of the organization of p-oxidation enzymes in mitochondria that supports the idea of intermediate channelling and explains the apparent absence of true intermediates of /3-oxidation from mitochondria.

The enzymes of mitochondrial beta-oxidation are thought to be organized in at least two functional complexes, a membrane-bound, long-chain-specific beta-oxidation system and a matrix system consisting of soluble enzymes with preferences for medium-chain and short-chain substrates. This hypothesis is supported by the observation that the inactivation of long-chain 3-ketoacyl-CoA thiolase by 4-bromotiglic acid (4-bromo-2-methylbut-2-enoic acid) causes the complete inhibition of palmitate beta-oxidation even though 3-ketoacyl-CoA thiolase, which acts on 3-ketopalmitoyl-CoA, remains partly active. The observed substrate specificities of long-chain acyl-CoA dehydrogenase (LCAD) and very-long-chain acyl-CoA dehydrogenase prompt the suggestion that LCAD is a functional component of the long-chain-specific beta-oxidation system. Altogether, a view is emerging of the organization of beta-oxidation enzymes in mitochondria that supports the idea of intermediate channelling and explains the apparent absence of true intermediates of beta-oxidation from mitochondria.