For the isolation of coeliac active peptide fractions the peptic tryptic digest of whole gliadin was successively separated by ultrafiltration, gel filtration, cation-exchange chromatography, anion exchange chromatography and high-performance liquid chromatography. After each separation step the peptide fractions obtained were characterized by amino acid analysis and examined for coeliac activity in an immunological test (LIF test) and in an organ-culture test. The most active fractions have molecular weights ranging from 7,000 to 14,000 daltons, high contents of Glx (greater than 40 mol-%), Pro (greater than 20 mol-%) and Phe (greater than 5 mol-%) and low contents of S-containing and basic amino acids (0 and less than 2.0 mol-%, respectively). The peptide fraction B3142 obtained after five separation steps seems to be a pure peptide, which shows activity in the immunological test for all coeliac patients examined in very low concentrations. This peptide consists of 53 amino acid residues and has the composition Glx24, Pro15, Val4, Phe3, Ser2, Leu2, Asx1, Gly1, Tyr1.
The coeliac active peptide B 3142, which has been isolated from a peptic-tryptic digest of gliadin and which consists of 53 amino-acid sequences, was partially hydrolyzed with alpha-chymotrypsin. The two fragment peptides CT-1 (positions 1-22 of B 3142) and CT-2 (positions 23-53) were separated by high-performance liquid chromatography on octadecyl silica gel and purified by gel filtration on Biogel P2. The examination in the organ-culture test including 18 coeliac patients on normal diet and 7 control persons have shown that the toxicity is preserved after the chymotryptic treatment and that the peptides B 3142, CT-1 and CT-2 do not significantly differ from one another according to their coeliac-specific effect.
Hydroxyurea (HU) inhibits the premeiotic DNA replication and the meiotic events that followed, namely readiness, recombination commitment, haploidisation, sporulation commitment and ascus formation. Short incubations with HU (2-4 hrs) during the premeiotic replication (i.e. starting between 3 and 6.5 hrs in sporulation medium) allow the resumption of the replication at a normal rate following the removal of the drug. The other meiotic events are similarly delayed by the approximate length of the treatment. In these experiments, intragenic recombination in ade2 reached a higher level than in the controls (x 1.3-2.0 in one pair of heteroalleles and x 3.0-4.0 in another pair). The recombination response to short HU treatments was not observed for a pair of heteroalleles in ade2 that normally shows a high level of meiotic recombination (750 per 10(6) cells), nor was the response observed in a pair of heteroalleles in lys2. HU treatments have almost no effect on sporulating cells from 8 hrs onwards. At 7-7.5 hrs the meiotic cells are very sensitive to the drug and even short treatments cause cell death and massive DNA degradation.
To determine the toxic effect of different gliadins on coeliac patients, which has been variably assessed in the literature, wheat prolamines (gliadin) were separated into the main fractions alpha-, beta-, gamma-, and omega-gliadins by chromatography on Sulfopropyl Sephadex C-50. The chemical compositions of the gliands were characterized by polyacrylamide gel electrophoresis, amino-acid analysis, determination of amide nitrogen and peptide maps. The peptide fractions B2 and B3 were isolated from the gliadins by a peptic tryptic digestion, ultrafiltration and gel filtration on Sephadex G-50. The gliadins and the peptide fractions were examined for coeliac activity by immunological tests (LIF tests) and by organ-culture tests. The results show that the peptide fractions are generally more active than their respective gliadins. The peptide fractions of all gliadins have a coeliac-specific toxic effect; their activities correlate with the chemical composition of the gliadins.
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