Stabilization of homogeneous preparations of pregnancy zone protein lyophilized in the presence of saccharose. Structural and functional studies.

Human pregnancy zone protein (PZP) is a macromolecule of 360 kDa, organized as a disulfide-linked homodimer of two 180 kDa subunits, with an amino acid sequence and structure remarkably similar to that of human alpha2-Macroglobulin. Homogeneous PZP samples undergo fast aging forming oligomeric aggregates of high molecular weight. This aged PZP loses its ability to interact with proteinases and consequently, non-recognition of receptors occurs. In the present work, we assessed the effect of saccharose on the stability of native PZP on lyophilized samples kept for a long period of time. Herein, we demonstrate that the addition of 0.25 M saccharose to homogeneous PZP and further lyophilization is enough to prevent aging and preserve functional activity for more than 1 year. Hence, high quality samples, in terms of purity, stability and functional activity will allow to develop biochemical studies in order to know the PZP role in physiological and pathological states where the protein levels are increased, such as pregnancy and tumoral disorders.