Manzamenones L–N,new dimeric fatty-acid derivatives from an Okinawan marine sponge Plakortis sp.

Three new polyketides, manzamenones L–N (1–3), have been isolated from an Okinawan marine sponge of the genus Plakortis. The structures of 1–3 were elucidated on the basis of spectroscopic data. Manzamenones L–N (1–3) were new dimeric fatty-acid derivatives consisting of a tetrahydroindenone with three carboxy groups and two hexadecanyl chains. Manzamenones M (2) and N (3) showed antimicrobial activity against several bacteria and fungi.     

Inhibitory effects of metachromins L–Q and its related analogs against receptor tyrosine kinases EGFR and HER2

Metachromins are a series of sesquiterpenoid quinones isolated from Okinawan marine sponges. Inhibitory effects of metachromins L–Q (1–6), sesquiterpenoid quinones with an amino acid residue, and their related analogs (7–18) prepared from metachromins A (19) and C (20) against receptor tyrosine kinases EGFR and HER2 were investigated. Two analogs 11 and 12 showed relatively stronger inhibitory activity against EGFR, while metachromins L–Q (1-6) and seven analogs (8, 10, 11, and 15–18) showed inhibitory activities against HER2.     

Intermolecular Forces Involved in the Gelation and Gel Stability of Sesame 13S Globulin

The effect of various reagents on the formation and stability of heat-induced gels of sesame 13S globulins were investigated. Electrostatic interaction, the hydrophobic bond and the disulfide bond were important for forming the network structure of gels, and the hydrogen bond also had an influence on the formation of the gel. Hydrophobic bonds mainly contributed to the stability of the gel. Subunit analyses of the proteins solubilized from the gels showed the presence of a free acidic subunit (AS) and basic subunit (BS), a polymer of AS, a dimer of BS and the dimer of a fragment from AS or BS. From the results, sulfhydryl-disulfide exchange reactions during gelation are suggested.     

Mechanism of the Acid-catalyzed Rearrangement of Thionocarbamates

A mixture of two thionocarbamates was subjected to the acid-catalyzed rearrangement. A sample of the reaction mixture was analyzed by glpc and resolved into four components. From the cross-over result, it has been concluded that the acid-catalyzed rearrangement of alkyl thionocarbamates into the isomeric thiolcarbamates proceeds by an intermolecular alkylating mechanism. This conclusion was supported by the detection of a transalkylated intermediate.     

Leucine Dehydrogenase from Corynebacterium pseudodiphtheriticum: Purification and Characterization

Leucine dehydrogenase [EC 1.4.1.9] was purified to homogeneity from Corynebacterium pseudodiphtheriticum ICR 2210. The enzyme consisted of a single polypeptide with a molecular weight of about 34,000. Stepwise Edman degradation provided the N-terminal sequence of the first 24 amino acids, and carboxypeptidase Y digestion provided the C-terminal sequence of the last 2 amino acids. Although the enzyme catalyzed the reversible deamination of various branched-chain l-amino acids, l-valine was the best substrate for oxidative deamination at pH 10.9 and the saturated concentration. The enzyme, however, had higher reactivity for l-leucine, and the k_cat/Km value for l-leucine was higher than that for l-valine. The enzyme required NAD⁺ as a natural coenzyme. The NAD⁺ analogs 3-acetylpyridine-NAD⁺ and deamino-NAD⁺ were much better coenzymes than NAD ⁺. The enzyme activity was significantly reduced by sulfhydryl reagents and pyridoxal 5′-phosphate. d-Enantiomers of the substrate amino acids competitively inhibited the oxidation of l-valine.     

The First and Second Dissociation Constants of Subtilisin BPN′-Plasminostreptin Complex Determined by a Polarographic Method,and the Effects of pH on Them

A polarographic method based on the Brdi?ka current (the polarographic catalytic hydrogen evolution current produced by proteins in the presence of cobalt salts) was applied to direct titration of subtilisin BPN′ (S.BPIST) with plasminostreptin (PS) at a concentration level of 10”⁸ m. The first and second dissociation constants of the S.BPN-PS complex were determined by fitting theoretical curves to the titration data, in which the multiple equilibria involving microscopically distinct forms of S.BPN-PS complex were taken into account. The intrinsic free energy change in the first binding of S.BPN′ to dimeric PS was larger than that in the second binding. The dependence of the microscopic dissociation constants of S.BPN′-PS complex on pH indicates the participation of ionizable groups of pK_a 8.0 and 9.4 in the complex formation. The repulsive effect between negatively charged molecules of S.BPN′ and PS in the complex formation at elevated pH is suggested.