Je. Brunet et M. Pulgar, DYNAMICS OF PROTOPORPHYRIN-IX IN THE HEME POCKET OF HORSERADISH-PEROXIDASE, Biochimica et biophysica acta, 1203(1), 1993, pp. 171-174
The local motion of protoporphyrin IX in the heme pocket of horseradis
h peroxidase has been studied using fluorescence methods. The temperat
ure dependence of the anisotropy and lifetime of a protoporphyrin IX-a
po-horseradish peroxidase complex, dissolved in a solution of 80% glyc
erol and 20% buffer (0.1 M phosphate, pH 7.4), was determined. Anisotr
opy data were analyzed in terms of the thermal coefficient of the fric
tional resistance to fluorophore movement. The resultant 'Y' plot was
characterized by three distinct slopes. The slope corresponding to the
lowest temperature regime agreed with the value obtained for fluoroph
ores not complexed with protein. The slope corresponding to an interme
diate temperature was lower indicating a larger resistance to porphyri
n rotation. At higher temperatures this resistance to rotation diminis
hed as evidenced by the increased slope. These results are contrasted
with those obtained with the protoporphyrin IX-apomyoglobin complex.