Binding Proteins and Receptors

1. Serum Binding

Human serum has been shown to bind PGs, presumably by strong noncovalent interactions. PGs bind tightly in inverse relation to their polarity. Thus, the order of tightness of binding is PGA > PGE1 > PGF2a. Since it is known that PGA, is cleared slowly in comparison to other PGs, its strong interaction with serum may explain its slow turnover. Specific binding proteins have not been reported.

2. Receptors

There appear to be three types of receptors located in various cell membranes. These receptors either raise or lower cellular levels of cyclic AMP or stimulate the phosphatidylinositol metabolic pathway (Table 16-4).

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