302 



F. LYNEN, S. OCHOA 



VOL. 12 (1953) 



The absorption spgctrum of S-acetoacetyl-N-acetyl thioethanolamine is shown in 

 Fig. 2. At pH 6.2 the compound has a band with a maximum at 233 m/x; this absorption 



peak is characteristic of the thioester bond^'^'^". At pH 8.0 

 an additional band appears with a maximum at 303 m/x.. Tliis 

 band is to be attributed to the formation of an enolate ion 

 and, as shown in Fig. 3, depends on the pH. The increasing 

 absorption parallels the increasing dissociation as the pH is 

 raised. The pK' of the compound was found to be 8.54. 



S-crotonyl-N-acetyl thioethanolamine was obtained in 



o 



220 



340 



260 300 



WAVELENGTH (m^) 



Fig. T. Ultraviolet absorption 

 spectrum of S-acetoacetyl-N- 

 acetyl thioethanolamine. 



CH,— CH = CH— C— S— CH,— CH,— NH^CO— CH, 



Fig. 3. pH Dependence of light ab- 

 sorption of S-acetoacetyl-N-acetyl 

 thioethanolamine at 313 m^w. 

 c = 5- io~^ M; d = i.o cm. 



crystalline form (m.p., 61.5-62°) through reaction of crotonyl 

 chloride with the lead salt of N-acetyl thioethanolamine^^. 



Its absorption spectrum is shown, along with that of free crotonate, in Fig. 4. It is 



evident that with the binding of the unsaturated acid to 



sulfur there is a shift toward longer wavelengths of the 



absorption due to the double bond. Free crotonate has 



a maximum (not shown on the figure) at 204 m fx while 



the thioester has a maximum at 224 m/x. The thioester 



has an additional band at 263 m/it which is possible due 

 O 



to the — C— S-group. The shift of the two absorption 



maxima toward longer wavelengths may be a reflection 



of the resonance between the double bond and the thio- 

 ester linkage, a fact which is of great importance for 



the chemical reactivity of the former. 



A number of S-acyl CoA derivatives of fatty acids 



have now become available through chemical or enzy mic 



synthesis. Solutions of acetoacetyl CoA can be readily prepared by the enzymic transfer 



of CoA from succinyl CoA to acetoacetate. This reaction has 

 made possible the isolation of acetoacetyl CoA**^ and its rou- 

 tine preparation for the assay of ^-ketothiolase. Succinyl 

 CoA itself can be prepared enzymically with a-ketoglutaric 

 dehydrogenase^* '2'^ or by means of the reaction between suc- 

 cinate, CoA, and ATP, of Kaufman etal.^^'". However, the 

 compound can be obtained much more readily by the syn- 

 thetic procedure of Simon and Shemin^^ with CoA-SH and 

 succinic anhydride. The method of Simon and Shemin has 

 further been applied to the preparation of other S-acyl CoA 

 derivatives such as acetyl, propionyl, butyryl, and crotonyl 

 CoA. S-acyl fatty acid derivatives have also been prepared by 

 means of the enzymic reaction of fatty acids witli CoA-SH 

 and ATP^^* and, in the case of the acetyl and propionyl 

 derivatives, through the phosphotransacetylasc catalyzed 

 reaction between CoA-SH and the corresi)onding acyl phos- 

 phates'*^. F"inally, S-acetoacetyl and S-/3-hydroxybutyryl 



220 



300 



240 260 280 

 WAVELENGTH (m/i) 

 I'lg. 4. Ultraviolet absorp- 

 tion spectra of S-crotonyl-N- 

 acetyl thioethanolamine (I), 

 crotonate (II), and N-acetyl 

 thioethanolamine (III), at 

 pH 7.0. 



References p. 31JIJ14. 



