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Abstract. Previous studies have shown that plasma membrane compounds are involved in the contactdependent inhibition of growth of human diploid fibroblasts. The purification of the active plasma membrane glycoprotein is described in this report. The glycoprotein has an apparent molecular mass of 60-70 kD and, due to differential sialylation, isoelectric points between pH 5.5. and 6.2. Treatment with sialidase yielded one spot in two-dimensional gel electrophoresis with an isoelectric point of 6.3. After removal of the N-glycosidically linked oligosaccharide chains, the apparent molecular mass is reduced by '~22 kD. Treatment was diluted NaOH, which removes the O-glycosidically linked portion of oligosaccharides, resulted in a reduction of the apparent molecular mass by '~5 kD. The addition of 50 ng/ml of this glycoprotein-for which the term "contactinhibin" is proposed-in immobilized form to sparsely seeded human fibroblasts resulted in a reversible 70-80% inhibition of growth. The inhibition was not confined to human fibroblasts as other cells were also inhibited, with the exclusion of transformed cells, which are refractory to contactinhibin. The inhibitory activity was abolished by treatment with B-galactosidase or glycopeptidase F, indicating that the glycan moiety is the biologically active part of the molecule.Confluent cultures treated with antibodies raised against contactinhibin were released from the contactdependent inhibition of growth. In addition to enhanced saturation density, these cultures exhibited a crisscross growth pattern and the formation of foci. Immunocytochemical studies showed that contactinhibin was associated with vimentin. Furthermore, contactinhibin was found to be not expressed in a speciesor organ-specific manner.

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Cytosolic epoxide hydrolase activity was measured towards trans-stilbene oxide in 41 human adult livers, in 40 fetal livers, in 17 placentas and in fetal and adult lungs, kidneys and gut. The cytosolic epoxide hydrolase activity was measurable in all specimens investigated. The rate of formation of trans-stilbene glycol (pmol/min per mg protein, mean +/- SD) was 55.2 +/- 89.6 (fetal liver). 303.2 +/- 73.2 (adult liver) and 18.8 +/- 13.1 (placenta) In the fetal extrahepatic tissues, the cytosolic epoxide hydrolase activity was 70.0 +/- 9.4 (adrenals), 47.6 +/- 7.2 (gut), 69.4 +/- 22.5 (kidneys) and 43.2 +/- 19.2 (lungs) pmol/min per mg protein, whereas in the adult tissues it was 131.2 +/- 63.1 (kidneys), 27.8 +/- 20.3 (intestine), 8.5 +/- 2.8 (lungs) and 7.2 +/- 4.2 (urinary bladder) pmol/min per mg protein.