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and P e d i a t r i c s , New Haven. Inherited methylmalonicacidemia (MM-emia) due t o d e f i c i e n t a c t i v i t y of methylmalonyl-CoA mutase may be caused by an abnormal mutase apoenzyme or by reduced holoenzyme a c t i v i t y secondary t o impaired synthesis of t h e mutase-requiring coenzyme, 5'-deoxyadenosylcobalamin (Ado-Cbl).. We studied Ado-Cbl synthesis i n 5 f i b r o b l a s t l i n e s from unrelated p a t i e n t s who have MM-emia due t o defective cobalamin (vitamin B12) metabolism. Their whole c e l l s i n c u l t u r e f a i l t o synthesize Ado-Cbl but make normal amounts of t h e other cobalamin coenzyme, methy lcobalamin.After breaking t h e c e l l s t o define t h e s t e p s i n Ado-Cbl synthesis, we assayed t h e f i n a l s t e p which combines the reduct i o n of cob(1I)alamin t o cob(1)alamin and the adenosylation of cob(1)alamin. Subcellular f r a c t i o n a t i o n s t u d i e s localized t h i s a c t i v i t y t o mitochondria. I n crude broken c e l l e x t r a c t s , enzyme a c t i v i t y was d e f i c i e n t or absent i n 3 of t h e 5 mutant c e l l l i n e s (4,0,0 pg Ado-~bl/mg protein/30 min;control l i n e s , 23 + 8). The other two MM-emia l i n e s had normal a c t i v i t i e s (23 and 17). These r e s u l t s e s t a b l i s h deficiency of Ado-Cbl synthesizing enzyme a s one cause of abnormal cobalamin metabolism and MM-emia. The two MM-emia l i n e s t h a t had normal enzyme a c t i v i t y suggest t h e r e i s f u r t h e r heterogeneity within the disorders of cobalamin metabolism a s well a s i n the MM-emia phenotype.IS CYSTINE ESSENTIAL FOR PREMATURE INFANTS? John I . Malone, John S. Curran, and Lewis A. Barness. Univ. of S. Fla. and Tampa General Hospital, Dept. of P e d i a t r i c s , Tampa 33620.Growth i n i n f a n t s (weight 1000-200f gms, 26-32 wks gestation) fed a commercially a v a i l a b l e low c y s t i n e formulawas not s i g n i f i c a n t l y d i f f e r e n t from those fed a formulation cont a i n i n g twice t h e d i e t a r y cystine. The formulas were i d e n t i c a l with t h e exception of p r o t e i n qua1ity;the low cystine formula contained 13mg/100ml and t h e high cystine formula 24mg/100ml. There was no s i g n i f i c a n t difference i n growth r a t e of i n f a n t s , i n t h e serum concentration o r t h e t i s s u e l e v e l s (glutathione) of c y s t i n e i n t h e two groups. Cystathionase act i v i t y i n t h e l i v e r has been reported t o be absent i n premature i n f a n t s . These r e s u l t s i n d i c a t e t h a t t h e low c y s t i n e formula contains adequate c y s t i n e f o r normal growth of premature inf a n t s & provides normal serum & t i s s u e l e v e l s of t h i s amino acid. W e have postulated (APS-SPR, Apr. '72) t h a t s h o r t and/or medium chain f a t t y acid accumulation i s important i n t h e pathogenesis of RS, causing mitochondria1 swelling. c e r e b r a l edema, hypoglycemia and f a t t y viscera. This study r e p o r t s gas chromatographic q u a n t i t a t ...

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