Journal
LABORATORY INVESTIGATION
Volume 84, Issue 3, Pages 292-299Publisher
NATURE PUBLISHING GROUP
DOI: 10.1038/labinvest.3700045
Keywords
formalin fixation; antigen retrieval; immunohistochemistry; ribonuclease A; enzyme histochemistry
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Funding
- NCI NIH HHS [1R21 CA091227-01] Funding Source: Medline
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Understanding the chemistry of protein modification by formaldehyde is central to developing improved methods to recover proteins from formalin-fixed paraffin-embedded tissues for proteomic analysis and to improve protein immunoreactivity for immunohistochemical studies. We used biophysical techniques to investigate the effects of formaldehyde treatment on bovine pancreatic ribonuclease A (RNase A). Treatment of RNase A with formaldehyde was shown by gel electrophoresis to lead to the rapid formation of intra- and intermolecular protein cross-links. Thermal studies revealed that these protein cross-links significantly increased the thermal denaturation temperature of RNase A preparations. Analysis of formaldehyde-treated RNase A oligomers isolated by gel chromatography revealed that intramolecular protein cross-links are primarily responsible for the increase in protein thermostability. Formaldehyde treatment also lowered the isoelectric point of the enzyme from 9.45 to the 6.0-7.4 range. Optical spectroscopic studies demonstrated that the formaldehyde-induced modifications did not significantly alter the secondary or tertiary structure of RNase A. Heating formaldehyde-treated RNase A at 65degreesC resulted in a significant reversal of the protein intra- and intermolecular cross-links and led to a partial restoration of enzymatic activity.
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