8. REACTIONS OF INORGANIC SUBSTANCES
377
of sulfur and sulfite by a process analogous to that suggested by Fromageot (102) for the formation of thiosulfate in mammals.
3. Thiosulfate
Tetrathionate was shown by Vishniac (103) to be the first intermediate in the oxidation of thiosulfate on the basis of various indirect
proofs such as the kinetic evolution of oxygen consumption during
Warburg oxidation of thiosulfate by resting cells of T. thioparus. Further
support is given by the finding that most thiobacilli oxidize tetrathionate, which may undergo transitory accumulation when these organisms
oxidize thiosulfate under certain experimental conditions. More recently,
Trudinger (104) demonstrated the formation of tetrathionate directly
with extracts of resting cells of Thiobacillus X, an organism which
closely resembles T. thioparus.
Ostrowski and Krawczyk (105) studied the mode of incorporation
of radioactivity into elementary sulfur and into cell constituents produced during the growth of T. thioparus in the presence of thiosulfate
labeled specifically on the "external" sulfur atom of the molecule:
(S
35 —S0 3 )
2 -
On the basis of their results, they concluded that the "internal" sulfur
atom of thiosulfate, i.e., the one carrying the sulfonic group, does not
enter the cell and is removed from the molecule directly as sulfate ion
which remains in the exocellular medium. According to Skarzynski and
Ostrowski (39), the sulfur atom carrying the sulfhydryl group passes
through the cell wall and combines with an unidentified acceptor to give
rise to organic compounds which are postulated to be the precursors of
cysteine, cystine, methionine, and thioctic acid. The final oxidation of
the "external" sulfur atom of thiosulfate to sulfate would then take
place after passage through these organic forms.
Trudinger (104) also employed thiosulfate molecules labeled with
S
35 in the "internal" or "external" position but did not confirm the conclusions of the preceding authors. In fact, he found no isotope exchange
between the internal and external sulfur atoms in the tetrathionate,
formed during these experiments; this shows that tetrathionate is produced in the cell by a process involving both sulfur atoms of thiosulfate,
12
2
112
2(S—S0 3 )
2 --> (0 3 S—S—S—S0 3 )
2 -
and consequently both must have effectively entered the cells.
By reducing to 10 seconds the incubation time of resting cells of
Thiobacillus X with labeled thiosulfate, Trudinger (104) established the
formation of another sulfur compound, in addition to tetrathionate,
377
of sulfur and sulfite by a process analogous to that suggested by Fromageot (102) for the formation of thiosulfate in mammals.
3. Thiosulfate
Tetrathionate was shown by Vishniac (103) to be the first intermediate in the oxidation of thiosulfate on the basis of various indirect
proofs such as the kinetic evolution of oxygen consumption during
Warburg oxidation of thiosulfate by resting cells of T. thioparus. Further
support is given by the finding that most thiobacilli oxidize tetrathionate, which may undergo transitory accumulation when these organisms
oxidize thiosulfate under certain experimental conditions. More recently,
Trudinger (104) demonstrated the formation of tetrathionate directly
with extracts of resting cells of Thiobacillus X, an organism which
closely resembles T. thioparus.
Ostrowski and Krawczyk (105) studied the mode of incorporation
of radioactivity into elementary sulfur and into cell constituents produced during the growth of T. thioparus in the presence of thiosulfate
labeled specifically on the "external" sulfur atom of the molecule:
(S
35 —S0 3 )
2 -
On the basis of their results, they concluded that the "internal" sulfur
atom of thiosulfate, i.e., the one carrying the sulfonic group, does not
enter the cell and is removed from the molecule directly as sulfate ion
which remains in the exocellular medium. According to Skarzynski and
Ostrowski (39), the sulfur atom carrying the sulfhydryl group passes
through the cell wall and combines with an unidentified acceptor to give
rise to organic compounds which are postulated to be the precursors of
cysteine, cystine, methionine, and thioctic acid. The final oxidation of
the "external" sulfur atom of thiosulfate to sulfate would then take
place after passage through these organic forms.
Trudinger (104) also employed thiosulfate molecules labeled with
S
35 in the "internal" or "external" position but did not confirm the conclusions of the preceding authors. In fact, he found no isotope exchange
between the internal and external sulfur atoms in the tetrathionate,
formed during these experiments; this shows that tetrathionate is produced in the cell by a process involving both sulfur atoms of thiosulfate,
12
2
112
2(S—S0 3 )
2 --> (0 3 S—S—S—S0 3 )
2 -
and consequently both must have effectively entered the cells.
By reducing to 10 seconds the incubation time of resting cells of
Thiobacillus X with labeled thiosulfate, Trudinger (104) established the
formation of another sulfur compound, in addition to tetrathionate,