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The amino acid sequences of three variants of the Kunitz-type trypsin inhibitors, Tia, Tib, and Tic, obtained from some cultivars of soybean were determined by conventional methods. All three inhibitors consisted of 181 amino acid residues. The differences in the amino acid sequences are as follows: Tia E12 G55 Y62 H71 S74 M114 L120 P137 L176; Tib S F N R V I T V; Tic E. The amino acid sequences of Pro(60)-Ser(61) and Asp(154)-Asp(155)-Gly(156)-His(157) of Tia reported previously (Koide & Ikenaka (1973) Eur. J. Biochem. 32, 417-431) were amended to Ser(60)-Pro(61) and His(154)-Asp-Asp-Gly(157), respectively.

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A hydroperoxide (HPO) lyase which catalyzes the specific cleavage of 13-L-hydroperoxy-cts-9,irans-11-octadecadienoic acid (13-L-c,£-HPO) to form n-hexanal was found in the homogenates of the soybeans such as Glycine max var. Suzuyutaka (normal type) and lipoxygenase (L) deficient mutant seeds (L-l null, L-2 null, L-3 null). A carbonyl compound which was formed from 13-L-c,í-HPO and 13-dl-c,£-HPO by the enzyme was n-hexanal. The enzyme was specific to the L isomer of 13-c,í-HPO. 9-D-i,c-HPO was not available for the enzyme reaction. Km and Vmax values of the enzyme for 13-L-c,£-HP0 were apparently similar among all the seeds. Apparent Vzmax value of the homogenate from L-2 null seed for linoleic acid was considerably lower (1/3-1/4) than those in the other seeds. It is concluded that a rate-determining step of n-hexanal formation from linoleic acid in L-2 null seed is a step of 13-L-c,£-HP0 formation by lipoxygenase. cross between P.I. 408251 (L-l null type) and Suzuyutaka. L-2 deficient mutant was a line from the cross between P.I.

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