Studies on esterolytic activity of alternative complement component factor B

Alternative complement component factor B was purified from human plasma and its esterolytic activity on various α-naphthylester derivatives was examined. Of these substrates, LeuAlaArg-naphthylester was the most susceptible. The K_m value of factor B for this substrate was about 5·10⁻⁴ M. 6-Amidino2-naphthyl-4-guanidinobenzoate inhibited the esterolytic activity of factor B. After activation of factor B, the esterolytic activity did not increase and the decayed form, Bb, cleaved the substrate to the same extent as factor B.