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Biosynthesis of Vitamins; Allosteric EnzymesЦRecent Results.

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groups prove to be much more susceptible to dehydrogenation than d o e s o substituents. In the norbornanols the order
is endo O H > ex0 OH > 7-OH. An endo OH in the presence
of vicinal exo OH is dehydrogenated at a considerably
slower rate than other endo groups. Furthermore, in theI2.2.11
system exo groups are dehydrogenated much faster in the
presence of a 7-syn O H group than in the presence of a
7-anti O H group. The behavior of the isomeric bicyclo[2.2.2]octane-2,6,7-triols illustrates unequivocally that intramolecular hydrogen bonds considerably increase the rate of
catalytic oxidation.
Lecture at Freiburg, February 6, 1970
[VB 234 IE]
German version: Angew. Chem. 82, 363 (1970)
["I Prof.
Dr. K. Heyns
lnstitut fur Organische Chemie u n d Biochemie
der Universitat
2 Hamburg, Papendamrn 6 (Germany)
Biosynthesis of Vitamins; Allosteric Enzymes
Recent Results
-
intermediate. Chorismic acid ( I ) can be converted into ( 2 )
in the presence of glutamine by an enzyme extract from the
mutant.
qOOH
YOOH
OH
NH,
Allosteric enzymes of the multiple-branched aromatic amino
acid,&biosynthetic pathway have been enriched from the
yeast Saccharomyces cerevisiae and from the fungus Cluviceps paspali. Chorismate mutase from C . paspali, which
converts ( I ) into prephenic acid (31, is inhibited by phenylalanine and tyrosine, and is activated by tryptophan. This
activation effect can be exploited for affinity chromatography
of the enzyme. Sepharose was activated with cyanogen
bromide and treated with tryptophan to give a carrier that
absorbs chorismate mutase. The enzyme is eluted with
tryptophan.
yoo"
c=0
By Franz Lingens [*I
Studies of vitamin biosynthesis in microorganisms employ
deficiency mutants having genetic blocks in their biosynthetic
(MNNG)
pathways. N-Methyl-N'-nitro-N-nitrosoguanidine
has proved a particularly effective mutagen for the production of such mutants. Treatment of DNA with N-trideuteriomethyl-N'-nitro-N-nitrosoguanidinea t p H 6 yields 7-trideuteriomethylguanine, thus ruling out exchange of deuteron
with solvent proton and hence the intermediacy of diazomethane in the methylation.
Action of M N N G o n a polyauxotrophic mutant of Aerobarter aerogenes, which produces large amounts of cborismic
acid ( I ) , yielded a p-aminobenzoic acid--mutant. This latter
mutant releases a nitrogen-containing intermediate into the
medium which is readily converted by acids into p-aminobenzoic acid. Structure (2) (3-enolpyruvic acid ether of 2,3dihydro-p-aminobenzoic acid) has been proposed for the
HOOC.
.
HO'. 'H
Activation of chorismate mutase with typtophan can be
used as a sensitive analytical tool for the determination of
this amino acid. It must, however, be borne in mind that
tryptophan homologs and analogs also display an activating
effect.
Lecture at Wuppertal on March 11, 1970
[VB 236 IE]
German version: Angew. Chem. 82, 398 (1970)
["I Prof. Dr. F. Lingens
Institut fur Mikrobiologie arid Molekularbiologie der
Universitat Hohenheim (Landwirtschaftliche Hochschule)
7 Stuttgart-Hohenheim, Kirchnerstrasse 30 (Germany)
SELECTED ABSTRACTS
The reactions of atomic and molecular halogens with silver
have been compared by R . J. Mclntyre and F. K . McTaggarr.
Atomic chlorine, bromine, and iodine were produced in a
flow system by a n electric discharge; the walls of the apparatus were prepared with phosphoric acid to minimize early
recombination of the halogen atoms. The rate of growth of
silver halide film was followed by means of a n interference
method. The halide film was found to inhibit further attack
of molecular halogens, whereas film thickness has no influence o n the reaction rate with atomic halogens. Low activation energies (around 5 kcal mole-]) and high reaction
probabilities (0.73 for I, 0.52 for Br, 0.25 for C1) were found
for the halogen atom reactions. / J. physic. Chem. 74, 866
(1970)/ -Hz.
[Rd 164 IE]
y = 89 "6', space group Pi. The exocyclic S-S
distance is
2.91 A. In the thiathiophthenes (2) the first and third of the
almost linearly arranged S atoms are ca. 4.7 8, apart. / Chem.
Commun. 1970, 154 / --Kr.
[Rd 173 IEI
Neutron energy-loss spectrometry is used by M . F. Collins,
B . C . Haywood, and G . C. Stirling for a study of the vibrational frequencies of hydrogen bonds. The instrument described allows the detection of resonances in the 400 to
The molecular structure of an"is0thiathiophthene" (1) has been
1400 cm-1 range. Because of the mass similarity, the techestablished X-ray crystallographically by R. J . S. Beer and
nique preferentially observes hydrogen motions, thus proD . Frew. The data support formulation of ( I ) as a-(4-pviding an advantage over I R and Raman spectroscopy. Coinbromophenyl-1,3-dithiol-2-ylidene)thioacetophenone rather
cidence of results with those of optical spectroscopy is dethan as a bicyclic system analogous to the thiathiophthene (2).
monstrated for KHFz, CsHC12, and CsDCIz. For NaHC03
This is surprising since a number of isothiathiophthenes and
and the acid potassium trifluoro- and trichloroacetates, the
thiathiophthenes resemble each other chemically and spechitherto unknown bending modes of the hydrogen bridges
t roscopical ly .
are identified. / J. chem. Physics 52, 1828 (1970). /-Hz.
( I ) , m.p. 200-203 "C, crystallizes as purple triclinic needles,
[Rd 170 IE]
~ = 1 7 . 7 7 5 ,b=7.190, ~ = 6 . 4 7 4 A , ~ = 9 0 ~ 5 5 ' , ~ = l l O " l ' ,
384
Angew. Chem. internat. Edit. 1 Vol. 9 (1970)
1 NO.5
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