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Activation of spinach pullulanase by reduction results in a decrease in the number of isomeric forms.

I Schindler1, A Renz, F X Schmid

  • 1Lehrstuhl für Pflanzenphysiologie, Universität Bayreuth, Germany.

Biochimica Et Biophysica Acta
|August 22, 2001
PubMed
Summary
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Spinach pullulanase microheterogeneity is explained by disulfide bridges forming between loops of its (beta/alpha)(8)-barrel structure. Reduction activates the enzyme, favoring highly active forms, while oxidation leads to less active forms.

Area of Science:

  • Biochemistry
  • Enzymology
  • Plant Science

Background:

  • Spinach starch debranching enzyme (pullulanase) exhibits microheterogeneity with multiple isomers of varying activity.
  • The enzyme's activity is modulated by reduction (activation) and oxidation (inactivation), but the structural basis for microheterogeneity is unknown.

Purpose of the Study:

  • To investigate the structural basis for spinach pullulanase microheterogeneity.
  • To determine how reduction and oxidation affect the enzyme's isomeric forms and activity.

Main Methods:

  • Enzyme activation/inactivation using thiol reagents (TCEP, GSH) and oxidation.
  • Quantification of isomer patterns using chromatofocusing.
  • Proteolytic digestion with trypsin and peptide sequencing.

Related Experiment Videos

Main Results:

  • Reduction with TCEP yielded a single, highly active pullulanase form resistant to trypsin.
  • Oxidation and GSH activation produced multiple peptides upon trypsin digestion, indicating loop cleavage.
  • Sequencing suggested disulfide bridges in loops connecting the (beta/alpha)(8)-barrel structure explain microheterogeneity.

Conclusions:

  • Disulfide bridges formed between loops of the (beta/alpha)(8)-barrel structure are proposed as the cause of spinach pullulanase microheterogeneity.
  • Enzyme activation via reduction favors specific conformations, while oxidation leads to structural changes affecting activity.
  • In vivo factors like chloroplast GSH concentration and pH fluctuations likely regulate pullulanase activity for starch metabolism.