Significant complement activation occurs in various disease entities. Selective and potent inhibition of certain complement enzymes may prove useful in the management of these diseases. This study is designed to define certain enzymes in the classical complement activation sequence using classical enzyme kinetics and then study certain inhibitors of these enzymes. The complement enzymes C42 and C423 will be studied. The initial velocity of substrate (C3 and C5 respectively) disappearance will be determined by measurement of residual functional complement activity in the enzyme-substrate mixture at times 30 seconds to 10 minutes after the addition of substrate to the enzymes. From these data, a Line-weaver-Burke plot will yield the values for the Michaelis constant and the maximum velocity of the reaction, the classical enzyme kinetic characteristics. The relationship of these two enzymes will be studied by competition of substrates for the active sites on the enzymes. Also the inter-relationships of the subcomponents of the enzymes will be determined by varying the quantitative relationship between the subcomponents and enzyme-substrate reaction. Subsequently various peptides will be tested for their ability to inhibit the enzymes. A potent and specific inhibitor will be sought for each enzyme. Using Lineweaver-Burke plots of the inhibited and non-inhibited enzymes, the nature of the completition will be defined (competitive, non-competitive, mixed competition). The affinity of the inhibitors for the enzymes, as described by the specific Ki's, will also be determined.