The eighth component of human complement. Purification and physicochemical characterization of its unusual subunit structure

The eighth component of human complement (C8) has been purified in high yield from Cohn Fraction III and characterized with regard to its physicochemical properties and subunit structure. The purified product was found to be similar to functional C8 isolated from plasma or serum. Human C8 possesses a molecular weight of 151,000 and is composed of a 1:1:1 ratio of three nonidentical subunits: alpha (Mr = 64,000), beta (Mr = 64,000), and gamma (Mr = 22,000). These subunits occur as a covalently linked alpha-gamma dimer which is noncovalently associated with beta. After purification and characterization of alpha, beta, and gamma, each was found to possess different amino acid compositions and NH2-terminal sequences. Both alpha and beta subunits contain similar but exceptionally high percentages of hydrophobic aromatic amino acids. As measured by circular dichroism, the secondary structure of C8 contains 12% alpha-helix, 24% beta structure, and 64% unordered structure, values typical of globular proteins. Complete secondary structure, as well as hemolytic activity, can be recovered after exposure to 6 M guanidinium hydrochloride or 8 M urea. The alpha-gamma and beta subunits were dissociated and isolated in the presence of sodium dodecyl sulfate and after removal of detergent, neither was found to possess independent hemolytic activity. Significantly, activity equivalent to that of native C8 was generated when alpha-gamma and beta were recombined in an equimolar ratio. These results indicate that C8 is an atypical serum protein with regard to both its subunit structure and denaturation characteristics.

Evaluation of teratogenicity and behavioral toxicity with inhalation exposure of maternal rats to trichloroethylene

Female rats were exposed by inhalation to trichloroethylene (TCE) vapors at a concentration of 1800 +/- 200 ppm to determine whether exposure before mating and during pregnancy is more detrimental to reproductive outcome than exposure either before mating alone or during pregnancy alone. Four treatment groups were utilized in a two by two factorial design: exposure to TCE for 2 weeks before mating and during the first 20 days of pregnancy; TCE before mating and filtered air during pregnancy; filtered air before mating and TCE during pregnancy; and filtered air before and during pregnancy. Significant elevations in skeletal and soft tissue anomalies, indicative of developmental delay in maturation rather than teratogenesis, were observed in the group exposed during pregnancy alone. The mixed function oxidase enzymes, ethoxycoumarin and ethoxyresorufin, indicative of cytochrome P-450 and P-448 activities, respectively, were measured in maternal and fetal livers, as well as livers of non-pregnant females, and showed variable levels of activity not uniformly related to treatment or pregnancy. Behavioral evaluation of offspring indicated a lack of treatment effect in tests of general activity levels at 10, 20 and 100 days of age. However, a reduction in postnatal body weights was seen in offspring from mothers with pregestational exposure. No results indicative of treatment-related maternal toxicity, embryotoxicity, severe teratogenicity or significant behavioral deficits were obtained in any of the treatment groups.