Immobilization of Pd onto Ti02 powders and colloids results in active photocatalysts for the selective reduction of C02/HC03" to formate. The active photocatalysts are prepared by adsorption of either aqueous Pd-d-cyclodextrin colloids (Pd(/S-CD)), synthesized at 60 °C, or aqueous Pd(citrate) colloids onto Ti02 powders or colloids. Illuminated Pd-free Ti02 suspensions, in the presence of C02/HC03" and the electron donor oxalate, generate H2 and a small amount of formate; formate is formed at a rate of 3.7 X 10~3 Mmol min'1. With Pd(/3-CD,60 °C)-Ti02 and Pd(citrate)-Ti02 suspensions, the photoconversion

SUMMARY1. In human blood, heroin is rapidly hydrolysed by sequential deacylation of two ester bonds to yield first 6-monoacetylmorphine (6-MAM), then morphine.2. Serum butyrylcholinesterase (BuChE) hydrolyses heroin to 6-MAM with a catalytic efficiency of 4.5/min per mol/L, but does not proceed to produce morphine.3. In vitro, human erythrocyte acetylcholinesterase (AChE) hydrolyses heroin to 6-MAM, with a catalytic efficiency of 0.5/min per mol/L under first-order kinetics. Moreover, erythrocyte AChE, but not BuChE is capable of further hydrolysing 6-MAM to morphine, albeit at a considerably slower rate.4. Both hydrolysis steps by erythrocyte AChE were totally blocked by the selective AChE inhibitor BW284c51 but were not blocked by the BuChE-specific inhibitor, iso-OMPA (tetraisopropylpyrophosphoramide).5. The brain synaptic form of AChE, which differs from the erythrocyte enzyme in its C-terminus, was incapable of hydrolysing heroin.6. Heroin suppressed substrate hydrolysis by antibodyimmobilized erythrocyte but not by brain AChE.7. These findings reveal a new metabolic role for erythrocyte AChE, the biological function of which is as yet unexplained, and demonstrate distinct biochemical properties for the two AChE variants, which were previously considered catalytically indistinguishable.

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