Postsynaptic density (PSD)-95, the most abundant postsynaptic scaffolding protein, plays a pivotal role in synapse development and function. Continuous palmitoylation cycles on PSD-95 are essential for its synaptic clustering and regulation of AMPA receptor function. However, molecular mechanisms for palmitate cycling on PSD-95 remain incompletely understood, as PSD-95 depalmitoylating enzymes remain unknown. Here, we isolated 38 mouse or rat serine hydrolases and found that a subset specifically depalmitoylated PSD-95 in heterologous cells. These enzymes showed distinct substrate specificity. ␣/␤-Hydrolase domain-containing protein 17 members (ABHD17A, 17B, and 17C), showing the strongest depalmitoylating activity to PSD-95, showed different localization from other candidates in rat hippocampal neurons, and were distributed to recycling endosomes, the dendritic plasma membrane, and the synaptic fraction. Expression of ABHD17 in neurons selectively reduced PSD-95 palmitoylation and synaptic clustering of PSD-95 and AMPA receptors. Furthermore, taking advantage of the acyl-PEGyl exchange gel shift (APEGS) method, we quantitatively monitored the palmitoylation stoichiometry and the depalmitoylation kinetics of representative synaptic proteins, PSD-95, GluA1, GluN2A, mGluR5, G␣ q , and HRas. Unexpectedly, palmitate on all of them did not turn over in neurons. Uniquely, most of the PSD-95 population underwent rapid palmitoylation cycles, and palmitate cycling on PSD-95 decelerated accompanied by its increased stoichiometry as synapses developed, probably contributing to postsynaptic receptor consolidation. Finally, inhibition of ABHD17 expression dramatically delayed the kinetics of PSD-95 depalmitoylation. This study suggests that local palmitoylation machinery composed of synaptic DHHC palmitoylating enzymes and ABHD17 finely controls the amount of synaptic PSD-95 and synaptic function.

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The OH reaction rate constants have been measured for CF3CH2OH, CF3CF2CH2OH, and CF3CH(OH)CF3 over the temperature range 250−430K. Kinetic measurements have been carried out using the discharge flow, laser photolysis, and flash photolysis methods, combined respectively with the laser-induced fluorescence technique to monitor the OH radical concentrations. The influence of impurities contained in the sample of CF3CF2CH2OH has been investigated by means of sample purification using gas chromatography. No sizable effect of impurities was found on the measured rate constants of these three fluorinated alcohols. The Arrhenius rate constants have been determined from the respective kinetic data as k(CF3CH2OH) = (2.00 ± 0.37) × 10-12 exp[−(890 ± 60)/T], k(CF3CF2CH2OH) = (1.40 ± 0.27) × 10-12 exp[−(780 ± 60)/T], and k(CF3CH(OH)CF3) = (6.99 ± 1.56) × 10-13 exp[−(990 ± 70)/T] cm3 molecule-1 s-1. A method of predicting the OH reaction rate constants for fluorinated alcohols, hydrofluorocarbons, alkanes, and alcohols has been proposed.

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The rate constants for the reactions of OH radicals with CH 3 OCF 2 CF 3 , CH 3 OCF 2 CF 2 CF 3 , and CH 3 OCF(CF 3 ) 2 have been measured over the temperature range 250-430 K. Kinetic measurements have been carried out using the flash photolysis, laser photolysis, and discharge flow methods combined respectively with the laser induced fluorescence technique. The influence of impurities in the samples was investigated by using gas-chromatography. The following Arrhenius expressions were determined: ϩ0.90 k(CH OCF CF ) ϭ (1.90 ) ϫ 3 2 3 Ϫ0.61 exp[Ϫ(1510 Ϯ 120)/T], exp[Ϫ(1540 Ϯ 80)/T], and 3 3 2

We have developed a technique for generating high concentrations of gaseous OH radicals in a reaction chamber. The technique, which involves the UV photolysis of O 3 in the presence of water vapor, was used in combination with the relative rate method to obtain rate constants for reactions of OH radicals with selected species. A key improvement of the technique is that an O 3 /O 2 (3%) gas mixture is continuously introduced into the reaction chamber, during the UV irradiation period. An important feature is that a high concentration of OH radicals [(0.53-1.2) × 10 11 radicals cm −3 ] can be produced during the irradiation in continuous, steady-state experiment. Using the new technique in conjunction with the relative rate method, we obtained the rate constant for the reaction of CHF 3 (HFC-23) with OH radicals, k 1 . We obtained k 1 (298 K) = (3.32 ± 0.20) × 10 −16 and determined the temperature dependence of k 1 to be (0.48 ± 0.13) × 10 −12 exp[−(2180 ± 100)/T] cm 3 molecule −1 s −1 at 253-328 K using CHF 2 CF 3 (HFC-125) and CHF 2 Cl (HCFC-22) as reference compounds in CHF 3 -reference-H 2 O gas mixtures. The value of k 1 obtained in this study is in agreement with previous measurements of k 1 . This result confirms that our technique for generating OH radicals is suitable for obtaining OH radical reaction rate constants of ∼10 −16 cm 3 molecule −1 s −1 , provided the rate constants do not depend on pressure. In addition, it also needed to examine whether the reactions of sample and reference compound with O 3 interfere the measurement when selecting this technique. C