Preparation of ³⁵S‐labelled l‐methionine and l‐cystine by biosynthesis

Abstract

S u m m a r y The modified method f o r b i o s y n t h e s i s o f L -m e t h i~n i n e -~~Sand L -~y s t i n e -~~S from baker's y e a s t (Saccharomyces c e r e v i s i a e ) is d e s c r i b e d . The y e a s t was c u l t i v a t e d i n a sulphur-deplated medium c o n t a i n i n g c a r r i e r -f r e e N a 35S04, under a i r bubbling dur i n g 24 hours. Yeast p r o t e i n s were hydrolyzed enzymatically i nt o f r e e amino a c i d s , a n d L -m e t h i~n i n e -~~S and L -c y~t i n e -~* S wer e i s o l a t e d by ion-exchange chromatography on a column. Radioa c t i v e y i e l d s f o r L -m e t h i~n i n e -~~S and L -~y s t i n e -~~S were 30% and lo%, r e s p e c t i v e l y . The obtained products have h i g h s p e c i f i c a c t i v i t y , l -l O C i / m o l , a n d radiochemical p u r i t y b e t t e r t h a n 95%.