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. J u l i c h , F.R.G. Selenium requirement i n children.LInder approved d i e t a r y treatment t h e d a i l y Se i n t a k e amounted only t o 1.0-4.7 ug i n p a t i e n t s with p h e n y l k e t m u r i a (PKU) o r maple-syrup-urihe d i s e a s e (MSUD). For 120 days 5 p a t i e n t s g a t an o r a l Se supplementation by y e a s t r i c h i n Se, d a i l y dose 0.56 g y e a s t , equivalent t o 45 ug Se. /Before supplementation t h e Se c o n t e n t s of serum and whole blood were reduced t o 5-16 ng/ml, 10-27 ng/ml reap., t h a t means t o 10-2C% normal. The a c t i v i t y of t h e e r y t h r o c y t e glut a t h i o n e peroxidase (OSHF'X) amounted on13 t o 0.19-2.69 U {g Hb. After 4-8 weeks of supplementation t h e Se c m t m t s o? serum and whole blood reached narmal values. The a c t i v i t y of t h e erythroc:rte GSHPx showed only a slow i n c r e a s e of t h e values a f t e r 4-6 weeks of Se supplementation. Within 9-15 weeks i t reached a p l a t e a u a t low normal v a l u e s -a time s i m i l a r t o normal r e d c e l l l i f e span. There was a c l o s e p o s i t i v e r e l a t i o n s h i p between t h e e r y t h r o c y t e Se content and t h e a c t i v i t~. of t h e e r y t h r o c y t e OSHPx.-Although mammalian GSHPx h a s been shown t o contain seleno-cyeteine r e s i d u e s i n polypeptide l i n k a g e , our knowledge about t h e Se r e q u i r m e n t s i n man i s s t i l l scarce. 36JD e p t . o f P a e d i a t r i c s , U n i v e r s i t y C o l l e g e H o s p i t a l , London, E n g l a n d .Atomic a b s o r p t i o n s p e c t r o p h o t o m e t r y (A.A.S.) f l a m e t e c h n i q u e s u s e 0 . 2 -0 . 5 ml p l a s m a . A.A.S. w i t h E l e c t r ot h e r m a l a t o m i s a t i o n i s more s e n s i t i v e a n d r e q u i r e s <20 p 1 o f p l a s m a , b u t c o n t a m i n a t i o n i s a p r o b l e m a n d i n t e rf e r e n c e from t h e p l a s m a m a t r i x p r e v e n t s t h e u s e o f a q u e o u s s t a n d a r d s . T h e r e f o r e t h e z i n c i n s h e e p s e r u m w a s removed w i t h C h e l e x 100 a n d t h e r e s i d u a l z i n c ( < 0 . 0 5 crg/ml) a n a l y s e d by f l a m e A .A.S . Z i n c s t a n d a r d s r a n g i n g f r o m 0.1 t o 2 . 0 bg/ml.Zn w e r e p r e p a r e d i n t h i s s e r u m .Only a c i d washed g l a s s , p o l y p r o p y l e n e o r P .T .F .E. equipment was u s e d . A s i n g l e 5 0 p l O x f o r d p i p e t t e t i p , o n c e c l e a n e d , was u s e d t o c h e c k t h e d i s t i l l e d w a t e r (<0.2ng/ml.Zn) a n d t h e n f o r t h e w h o l e d a y s work, b e i n g r i n s e d i n 5% A r i s t a r HN03x10 a n d H20x10 b e t w e e n i n j e c t i o n s . S t a n d a r d s a n d s a m p l e s w e r e d i l u t e d 1 : 2 0 0 by a Micromedic d i l u t e r i n t o p o l y p r o p y l e n e t u b e s a n d 5 0 p l i n j e c t i o n s made i n t o t h e f u r n a c e . P r e c i s i o n s t u d i e s g i v e a C o e f f i c i e n t o f v a r i a t i o n o f 2.5%.Recovery e x p e r i m e n t...