Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.4.21.1 (chymotrypsin)
 10,938 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Rabbit liver cytosolic serine hydroxymethyltransferase exists in several subforms which have different isoelectric points. Incubation of the purified enzyme with chymotrypsin cleaves the enzyme at Trp14. The released amino-terminal 14-mer peptide was shown to exist in three forms of equal concentration. The peptides differ in structure only at the asparaginyl residue at position 5. In addition to asparagine at this position we found both aspartyl and isoaspartyl residues. The deamidation of Asn5 does not appear to occur during the purification of the enzyme. The in vitro rate of deamidation of Asn5 in the enzyme is more than 5-fold slower than the rate of deamidation of this residue in the free 14-mer peptide. The isoaspartyl residue at position 5 serves as a substrate for protein carboxyl methyltransferase both in the free 14-mer peptide and the native enzyme. The enzyme which has had the amino-terminal 14 residues removed by digestion with chymotrypsin still exists in several forms with different isoelectric points. Reaction of peptides from this enzyme with carboxyl methyltransferase suggests that there is at least one more asparaginyl residue in this enzyme other than Asn5 which has undergone deamidation with the formation of isoaspartyl bonds.
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PMID:Evidence for the in vivo deamidation and isomerization of an asparaginyl residue in cytosolic serine hydroxymethyltransferase. 231 67

Rabbit liver cytosolic serine hydroxymethyltransferase exists as a set of subforms which exhibit different isoelectric points. Previous studies have shown that deamidation of an asparagine residue at position 5 of the amino acid sequence accounted for some of the charge heterogeneity (Artigues, A., Birkett, A., and Schirch, V. (1990) J. Biol. Chem. 265, 4853-4858). The present study has also identified asparagine 220 as being partially deamidated. An estimated 25-30% of the purified enzyme contains an isoaspartyl residue at position 220. This suggests that deamidation of asparagine 220 occurs by the beta-aspartyl shift mechanism. Western blot analysis of purified cytosolic serine hydroxymethyltransferase, after isoelectric focusing under reducing and denaturing conditions, showed four subforms of the individual subunits with respect to isoelectric point. Extracts from 3-day- and 3.5-year-old rabbit livers showed the presence of these same four subunit subforms. Purified cytosolic serine hydroxymethyltransferase was found to be degraded in 24 h after mechanical injection into Xenopus laevis oocytes. However, when the first 14 amino acid residues are removed from the enzyme by digestion with chymotrypsin, leaving a fully catalytically active enzyme, the rate and extent of degradation of the truncated enzyme in oocytes were significantly reduced. One of the deamidated asparagine residues is at position 5, suggesting that this deamidation site may be a signal for degradation of the enzyme.
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PMID:Cytosolic serine hydroxymethyltransferase. Deamidation of asparaginyl residues and degradation in Xenopus laevis oocytes. 831 47