Effects of gold salts and penicillamine on serum complement

The effects of the gold salt sodium aurothiomalate and of d-penicillamine on complement were studied in vitro. Total haemolytic complement was inhibited by 0.05-1mM gold. The inhibitory potency of gold was inversely correlated to the concentration of complement in the system, but was not diminished by albumin or decomplemented serum protein in concentrations approaching those circulating in blood. Penicillamine which itself slightly inhibited complement, prevented or reversed the action of gold. Conversion of C1s to C1esterase was not inhibited. Gold inhibited the action of C1esterase on component C4, but not the action on small-molecular synthetic ester substrates. Only very high gold concentrations (375-560 microM) inhibited the conversion of C3 to C3b. No inhibition of the alternative pathway was detected.