Takashi Tatsuno

A novel method for the determination of C-terminal amino acid in polypeptides by selective tritium labelling

Abstract In our previous communication ( Matsuo, 1965 ), we reported selective 2H- and 3H-labelling reaction at the C-terminal amino acid of several N-acetylpeptides through the C-terminal racemization mechanism. The selective deuteration or tritiation is based upon the C-terminal oxazolone formation in peptides by the action of acetic anhydride or dicyclohexylcarbodiimide, followed by the base-catalyzed hydrolytic ring-opening in deuterium oxide or tritium oxide as shown in the following scheme. The above selective C-terminal tritiation has now been applied to the determination of the known C-terminal amino acids of angiotensin II ( Skeggs, 1955 ) and beef-insulin ( Sanger, 1955 ). The experimental results described in this communication will indicate that the C-terminal determination of polypeptides or proteins may be accomplished in a simple manipulation and in a micro-scale by this method. A modification of the above procedure for identifying C-terminal aspartic acid and proline, which were two exceptions that resisted the oxazolone formation by the above method, will also be described.

Selective inhibition of 5-lipoxygenase by natural compounds isolated from Chinese plants, Artemisia rubripes Nakai.

Three of four natural compounds, which are caffeic acid, eupatilin and 4′‐demethyleupatilin, isolated from Chinese plant, Artemisia rubripes Nakai selectively inhibited 5‐lipoxygenase of cultured mastocytoma cells. Half‐inhibition doses (ID 50) for caffeic acid, eupatilin and 4′‐demethyleupatilin were 3.7, 14 and 18 × 10−6 M, respectively. The inhibition by caffeic acid was non‐competitive types. Prostaglandin synthase activities were little inhibited by eupatilin and 4′‐demethyleupatilin, but rather stimulated by affeic acid. The formation of leukotriene C4 and D4 by mast tumor cells was almost completely suppressed by these compounds at 10−4 M.

Trichothecene structure and toxicity to the green alga Chlorella pyrenoidosa.

Using the paper-disk method with Chlorella-seeded agar plates, 15-acetoxyscirpenol, HT-2 toxin, acetyl T-2 toxin and neosolaniol inhibited growth at a concentration of 1 mg/ml, whereas verrucarol, T-2 tetraol, nivalenol, fusarenon-X, deoxynivalenol and 3-acetyldeoxynivalenol were inactive. Taking into account that verrucarin A, roridin A, T-2 toxin and diacetoxyscirpenol had previously been found to strongly inhibit Chlorella growth, esterification at R15 appears to be important for growth inhibitory activity. The most active agents are also esterified at R4. Inhibition of protein synthesis appears to be involved in the toxicity.

Modification of α-santonin VI. Synthesis of (+)-deoxyvernolepin

Abstract (+)-Deoxyvernolepin is synthesized from α-santonin via angular methyl activation and subsequent furan ring opening.

Acceleration of actin polymerization and rapid microfilament reorganization in cultured hepatocytes by cyclochlorotin, a hepatotoxic cyclic peptide.

Cyclochlorotin (= chloropeptide, CC) is a hepatotoxic mycotoxin of Penicillium islandicum Sopp. The effect of CC on actin polymerization was examined by the measurement of changes in fluorescence intensity using pyrene-labeled actin and high shear viscosity. In the presence of CC, the time course of actin polymerization was accelerated in a dose dependent manner (2.5 ng/ml-2.5 microg/ml), without affecting the final level of viscosity. CC exerted a strong stabilizing effect on actin, enabling it to maintain its filamentous form in the presence of members of actin-binding proteins, including those of the gelsolin family prepared from hepatocytes. Microscopic observation revealed that in cultured hepatocytes, 1.0 microg/ml of CC induced bleb formation and changes in the microfilament. These observations indicated that after contact of the hepatocyte with CC, the following events were probable. The toxin passed through the cell membrane by a transport system and immediately reacted with the actin-actin binding proteins underlying the lipid bilayer. Bleb formation and hepatotoxicity were thus induced.

Structure of lslandic acid, a new metabolite from Penicillium islandicum Sopp.

The structure of islandic acid a new anit-tumour metabolite isolated from P. islandicum Sopp., has been determined by the application of 13C–{1H} long range selective proton decoupling experiments on its methyl ester.