The two activities of chicken liver 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase were inactivated by o-phthalaldehyde. Absorbance and fluorescence spectra of the modified enzyme were consistent with the formation of an isoindole derivative (1 mol/mol of enzyme subunit). The inactivation of 6-phosphofructo-2-kinase by o-phthalaldehyde was faster than the inactivation of fructose-2,6-bisphosphatase, which was concomitant with the increase in fluorescence. The substrates of 6-phosphofructo-2-kinase did not protect the kinase against inactivation, whereas fructose-2,6-bisphosphate fully protected against o-phthalaldehyde-induced inactivation of the bisphosphatase. Addition of dithiothreitol prevented both the increase in fluorescence and the inactivation of fructose-2,6-bisphosphatase, but not that of 6-phosphofructo-2-kinase. It is proposed that o-phthalaldehyde forms two different inhibitory adducts: a non-fluorescent adduct in the kinase domain and a fluorescent isoindole derivative in the bisphosphatase domain. A lysine and a cysteine residue could be involved in fructose-2,6-bisphosphate binding in the bisphosphatase domain of the protein.
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Research Article| August 15 1989
Inactivation of liver 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase by o-phthalaldehyde
M H Rider ;
Biochem J (1989) 262 (1): 97–102.
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M H Rider, L Hue; Inactivation of liver 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase by o-phthalaldehyde. Biochem J 15 August 1989; 262 (1): 97–102. doi: https://doi.org/10.1042/bj2620097
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