SUMMARY: After growth of strain , the culture fluid and organisms contained an amino acid which gave a yellow-brown colour with ninhydrin. This compound was shown by comparison with synthetic material to be -succinylhomoserine believed from previous work with this strain to be a methionine precursor. Its accumulation gave proof that it was formed in large amounts by the growing organisms. The formation of -succinylhomoserine occurred equally well in the presence or absence of added homoserine and succinate, but when the succinate was added to growth media, synthesis occurred preferentially from it and the utilization of endogenously-formed succinate was diminished. Without added homoserine the extent of accumulation was such (up to 440 mg. -succinyl-homoserine/1.) that homoserine synthesis may have been increased above normal to provide the required quantities (up to 240 mg./1.) of homoserine. Methionine completely suppressed accumulation of -succinylhomoserine, threonine and lysine had no effect. A cystathionine-requiring mutant of also accumulated -succinylhomoserine; the amount (20-30 mg./1.) being only about of that given by , and methionine prevented its accumulation by this organism too. It appears that the methionine synthesis pathway in is very similar to that in and is subject to end-product control.


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