Stopped-Flow Study of the Cationic Polymerization of Styrene Derivatives. 1. Direct Observation of the Propagating Species in the Polymerization of p-Methoxystyrene in 1,2-Dichloroethane

1978 ◽  
Vol 11 (2) ◽  
pp. 328-332 ◽  
Author(s):  
Mitsuo Sawamoto ◽  
Toshinobu Higashimura
Keyword(s):  
Direct Observation ◽  
Cationic Polymerization ◽  
Stopped Flow ◽  
Styrene Derivatives ◽  
Flow Study

scholarly journals Reactions of DOPA (3,4-dihydroxyphenylalanine) decarboxylase with DOPA

1979 ◽  
Vol 183 (2) ◽  
pp. 361-368 ◽  
Author(s):  
A Minelli ◽  
A T Charteris ◽  
C B Voltattorni ◽  
R A John
Keyword(s):  
Steady State ◽  
Time Scales ◽  
Direct Observation ◽  
Equilibrium Constants ◽  
Active Part ◽  
Stopped Flow ◽  
Step Rate ◽  
Multiple Reactions ◽  
Absorbing Material ◽  
Different Time Scales

The study of DOPA (3,4-dihydroxyphenylalanine) decarboxylase by steady-state methods is difficult because multiple reactions occur. The reaction with DOPA was studied at enzyme concentrations between 20 and 50 micrometer by direct observation of the bound coenzyme by using stopped-flow and conventional spectrophotometry. Four processes were observed on different time scales and three of these were attributed to stages in the decarboxylation. The fourth was attributed to an accompanying transamination that renders the enzyme inactive. It was clear that much, if not all, of the 330 nm-absorbing coenzyme present in the free enzyme plays an active part in the decarboxylation, since it is converted into 420 nm-absorbing material in the first observable step. An intermediate absorbing maximally at 390 nm is formed in a slower step. Rate and equilibrium constants have been determined and the ratio of decarboxylation to transamination was estimated to be 1200:1.

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