N U C L E I C A C I D S A N D S U L P H Y D R Y L G R O U P S
285
FIG. 21. Same experiment as in Fig. 2 0 , but treated for 1 day with lipoic acid
(20 μg|m\), 3 days ATP (0-1 mg/ml) and 3 days in normal Niu-Twitty medium. Note the
complete closure of the nervous system.
it is certain t h a t , in a m p h i b i a n eggs, t h e t w o substances h a v e v e r y
definite additive effects, i.e., d e v e l o p m e n t is blocked b y a m i x t u r e of
lipoic acid a n d m e r c a p t o e t h a n o l a t concentrations which, if used alone,
exert little influence on morphogenesis.
I t h a s been r e p o r t e d b y E a k i n a n d his co-workers t h a t oxaloacetate
reverses t h e effects of lipoic acid. According t o a recent p a p e r b y
H e n d e r s o n a n d E a k i n (1960), lipoic acid is a powerful inhibitor of malic
d e h y d r o g e n a s e ; this would explain w h y oxaloacetate antagonizes t h e
inhibitory effects of lipoic acid on morphogenesis.
W e also observed t h a t oxaloacetate, a n d t o a lesser e x t e n t succinate,
often exert favourable effects on a m p h i b i a n eggs t r e a t e d w i t h lipoic acid
e x t e n t of A D P , b u t n o t of A M P ) definitely improves t h e closure of the
neural tube in t h e lipoic acid-treated e m b r y o s (Figs. 20, 21).
E x p e r i m e n t s are still in progress t o establish w h e t h e r or n o t m e r c a p t o -
ethanol a n d lipoic acid a c t on t h e s a m e metabolic step. I n this respect,
285
FIG. 21. Same experiment as in Fig. 2 0 , but treated for 1 day with lipoic acid
(20 μg|m\), 3 days ATP (0-1 mg/ml) and 3 days in normal Niu-Twitty medium. Note the
complete closure of the nervous system.
it is certain t h a t , in a m p h i b i a n eggs, t h e t w o substances h a v e v e r y
definite additive effects, i.e., d e v e l o p m e n t is blocked b y a m i x t u r e of
lipoic acid a n d m e r c a p t o e t h a n o l a t concentrations which, if used alone,
exert little influence on morphogenesis.
I t h a s been r e p o r t e d b y E a k i n a n d his co-workers t h a t oxaloacetate
reverses t h e effects of lipoic acid. According t o a recent p a p e r b y
H e n d e r s o n a n d E a k i n (1960), lipoic acid is a powerful inhibitor of malic
d e h y d r o g e n a s e ; this would explain w h y oxaloacetate antagonizes t h e
inhibitory effects of lipoic acid on morphogenesis.
W e also observed t h a t oxaloacetate, a n d t o a lesser e x t e n t succinate,
often exert favourable effects on a m p h i b i a n eggs t r e a t e d w i t h lipoic acid
e x t e n t of A D P , b u t n o t of A M P ) definitely improves t h e closure of the
neural tube in t h e lipoic acid-treated e m b r y o s (Figs. 20, 21).
E x p e r i m e n t s are still in progress t o establish w h e t h e r or n o t m e r c a p t o -
ethanol a n d lipoic acid a c t on t h e s a m e metabolic step. I n this respect,