[Contribution to the study of labeled neurohypophysial hormones. Preliminary data on the properties of the macromolecular compound: vasopressin-dextran (author's transl)]

The neuropeptide binding sites at the level of their target cells can be localized by several morphological methods. For one of the neurohypophysial hormones, vasopressin, not all labelling techniques can be applied: radioiodinated vasopressin has no biological activity; only 3Hvasopressin can be used. Immunocytochemical evidence for vasopressin receptors must be supported by complementary data in order to demonstrate the specificity of the binding. A new labelled ligand is prepared: vasopressin-dextran. In vivo, this macromolecular compound has antidiuretic properties equivalent to those of free vasopressin. In vitro, it gives a cross reaction with specific anti-vasopressin antibodies. For the same macromolecular compound, the ratio between the conjugated vasopressin estimated through R.I.A. and that assayed by biological method was 30.

Direct evidence for internalization of mitochondrial aspartate aminotransferase into mitoplasts

Mitochondrial aspartate aminotransferase, an enzyme localized on the inner face of the inner mitochondrial membrane, is released into the intermembrane space upon addition of a "movement effector" (succinate, fumarate, pyruvate, or glutamate) [Waksman, A., & Rendon, A. (1974) Biochimie 56, 907-924]. After removal of the movement effector, 90% of the released enzyme rebound to mitoplasts. Lubrol fractionation showed that this bound activity was associated with the inner membrane. Internalization was demonstrated by using both enzymatic and molecular approaches. It was found that 70% of the reassociated enzyme became inaccessible from the outside of the mitoplast either to a nonpermeating substrate (NADH), to mild protease hydrolysis, or to recognition by a specific antibody. In contrast, in inside-out vesicles, the enzyme remained accessible to NADH, protease, and antibodies. Latency measurements performed at different temperatures on whole intact mitochondria confirmed the existence of reversible intermembrane movement of the enzyme in situ.

Soluble biospecific macromolecule for purification of estrogen receptor

An alternative to affinity chromatography purification of proteins based on the use of a water-soluble biospecific polymer has been applied to the estrogen receptor from calf uterus. The receptor (4S-trypsin form) was bound to a dextran-estradiol conjugate (molecular weight approximately 500,000) and the complex was isolated by gel filtration. Highly purified receptor was subsequently released from the dextran-estradiol conjugate by exchange with [3H]estradiol.

Induction of maturation in Xenopus laevis oocytes by a steroid linked to a polymer

A progesterone analog has been covalently linked via an amide bond to polyethylene oxide (molecular weight, 20,000). This macromolecular steroid molecule displays the biological activity of progesterone in inducing meiotic maturation when incubated with Xenopus laevis oocytes (stage VI) in vitro. Its efficiency (half-maximum effective concentration, 30 muM) is approximately 10 times lower than that of its low molecular weight homolog (3 muM). Control experiments with polyethylene oxide and an estradiol derivative (up to 1 mM) assessed the specificity of the progesterone macromolecular analog. Uptake experiments using radioactive derivatives revealed a small (if not negligible) intake of the macromolecular progesterone analog by the oocytes compared to that of free steroids, and no parallelism was found between radioactivity incorporation and effect. The possibility of cleavage of the macromolecular derivative during the incubation was ruled out. Furthermore, injection of the polymer-linked progesterone into the oocytes did not induce maturation. These observations suggest that the macromolecular progesterone analog itself is responsible for the biological effect and that the presence of this compound inside the cell is neither necessary nor sufficient for triggering reinitiation of meiosis. These conclusions are in agreement with the proposal that interaction with the plasma membrane of the oocyte is necessary for progesterone action in this particular system, in contrast to the case of somatic cells which have intracellular steroid receptors.