[Fluorescent studies on conformational states of human plasminogen. I. pH effect]

Conformational transitions of human plasminogen were studied by the fluorescent analysis according to the shift of the fluorescence spectrum maximum and the fluorescence dynamic quenching method. At pH 9.0-6.0 plasminogen has a stable native conformation, with a decrease of pH from 6.0 down to 5.3 the fluorescence spectrum maximum moves towards the short-wave region and with the subsequent lowering of pH--to the long-wave region. A share of the available protein tryptophanyls to quenchers KI and acrylamide in the neutral and weak-acid media is determined. The analysis of the data obtained permits considering that the plasminogen molecule at pH 5,3 is of a more compact structure than at pH 7.0; at pH 2.0 it loosens preserving the compact packing.