Studies on the catalytic activity of human hepatic porphobilinogen deaminase.
Porphobilinogen deaminase was purified from human hepatocytes. A variety of group specific reagents have been used to achieve site-specific modifications to evaluate the potential role of such groups in the whole catalytic cycle. Treatment with dicarbonyl reagents caused a rapid loss in activity that was time and concentration, dependent. Protection experiments revealed that arginine residues are involved in the binding of the substrate. Treatment with Woodward's reagent K showed the fastest inactivation of deaminase (85% in 30 sec at 30mM) which was pH dependent and could be prevented by the presence of substrate, suggesting that deprotonated carboxylated groups from Asp/Glu are essential for catalytic activity. Kinetic analysis gave values of 0.3 sec-1 for the k3 rate constant and 8x10-2 M for the KI of the non covalent complex between deaminase-Woodward's Reagent K.
Mazzetti
M B
MB
Departmento de Química Biológica, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Buenos Aires, Argentina.
Tomio
J M
JM