The sulphur metabolism of mould fungi: The use of “biochemical mutant” strains of Aspergillus nidulans in elucidating the biosynthesis of cystine

Biochemical Genetical Studies on the Pathway of Sulphate Assimilation in Aspergillus nidulans

“…It is clear from these results that, according to their nutritional requirements, the mutants can be classified into 4 groups which will be called groups A , By C and L) as indicated in Table 1. It appears that the simplest explanation for these findings as well as those reported earlier (Lederberg & Tatum, 1946;Hockenhull, 1949) may be provided by the following scheme of sulphate assimilation : Thiosulphate as intermediate As already mentioned, it has been established that the reduction of sulphate to sulphite is an obligatory step in the microbial synthesis of sulphur-containing amino acids from sulphate. It has also been suggested that in Neurospora mmsa methionine is formed from cysteine through the cystathionine pathway (Teas, Horowitz & Fling, 1948;Fling & Horowitz, 1951).…”

“…It may be noted that in all the previous work with A . nidu2ans (Hockenhull, 1949;Shepherd, 1956) it has been assumed that cysteine is formed from thiosulphate by way of cysteine-S-sulphonate. Although Shepherd (1956) claimed that sulphate sulphur combines with the carbon chain at the sulphite stage in the normal assimilatory metabolism, it does not seem possible to explain the results described either in the present paper or in that of Hockenhull (1949) by assuming such a pathway.…”

“…This pathway was proposed by Horowitz (1950), based on observations with nutritional mutants of Newospora crassa. It has further been suggested from studies with mutant strains of Aspergillus nidulans that thiosulphate reacts with serine to give cysteine-S-sulphonate as an intermediate in the biosynthesis of cysteine (Hockenhull, 1949). Shepherd (1956) also considered this possibility, but denied the involvement of thiosulphate in the main route of sulphate assimilation.…”

Nutritional Studies of Cysteineless Mutants of Salmonella typhimurium

“…The pathway of cyst(e)ine biosynthesis has previously been studied in a variety of micro-organisms including Escherichia coli (Lampen, (Phinney, 1948; Horowitz, 1950Horowitz, , 1955; AspergiZlus nidulans (Hockenhull, 1949; Shepherd, 1956); A . niger (Steinberg, 1941).…”

The distribution of methionine loci in Neurospora crassa

“…Most of the evidence from .Neurospora crassa (Horowitz, 1955), and from a variety of microorganisms (Steinberg, 1941 Lampen, Roepke andJones, 1947;Hockenhull, 1949;Clowes, 1958), indicates that the initial stages of methionine synthesis, in which cysteine is produced from inorganic sulphate, involve the reduction of sulphate via sulphite and thiosulphate before the sulphur is incorporated into an organic compound.…”