Keiichi Aso

Trypsin-catalyzed Oligomerization of L-Lysine Esters

The oligomerization of L-lysine esters with a free α-amino group was done using trypsin as a catalyst in aqueous media, and some reaction parameters were examined. The pH-dependence of the reaction suggested that aminolysis by the substrate species having non-protonated α- and ɛ-amino groups was a dominant factor governing the reaction progress. At the beginning of the reaction lysine oligomers containing up to 8 residues were observed, but much of the dimer was accumulated during prolonged incubation due to secondary hydrolysis of highly polymerized products. The reaction yield depended on the ratio of enzyme and substrate; an overall reaction yield higher than 70% was attained after 2 hr of reaction when 1,000 mM of L-lysine ethyl ester was treated with 200 μM of trypsin at pH 10.0. The oligomerization was apparently enhanced by an addition of NaCl and by using the longer alkyl esters.

Trypsin-catalyzed synthesis of the arginyl-arginine dipeptide froml-arginine ethyl ester

SummaryTrypsin has been found to catalyze oligomerization ofl-arginine ethyl ester in aqueous reaction media. More than 40% of the substrate has been converted mostly to arginyl-arginine under the optimized reaction conditions (pH 10; [trypsin]≥10μM; [substrate]≥0.5M).

Tryptophan-, Threonine-, and Lysine-enriched Plasteins from Zein

(1974). Tryptophan-, Threonine-, and Lysine-enriched Plasteins from Zein. Agricultural and Biological Chemistry: Vol. 38, No. 3, pp. 679-680.

PEG-papain catalyzed synthesis of a Kyotorphin derivative in aqueous organic media

SummaryPEG-papain catalyzed synthesis of a Kyotorphin derivative has been investigated in aqueous organic solvents using Bz-Tyr-OEt and Arg-OMe as substrates. PEG-papain has shown increased resistance to high pH and high ethanol concentration; 42 % of Bz-Try-OEt has been converted to Bz-Tyr-Arg-OH under the optimized reaction condition (pH 7.0–9.0; 40 % EtOH).

Location and State of Methionine Residues in a Papain-synthesized Plastein from a Mixture of Soybean Protein Hydrolysate and l-Methionine Ethyl Ester

With the aid of papain, a plastein was synthesized from a 1 : 10 mixture of l-methionine ethyl ester and a peptic hydrolysate of soybean protein. Dialysis of the whole reaction-product yielded a methionine-incorporated plastein (Met-plastein) as the nondialyzable fraction, its yield being 78.2% on a dry-matter basis, of the whole reaction-product. Methionine content in this Met-plastein was 7.22% on a weight basis, while its content in the material hydrolysate was only 1.25%. Carboxypeptidase A treatment of Met-plastein liberated methionine at an outstandingly rapid rate. A similar, but not so outstanding, rate was observed for the methionine liberation from Met-plastein by treatment with leucine aminopeptidase. Methyl isothiocyanate treatment and subsequent cyclization yielded a mixture of methylthiohydantoins from Met-plastein. Gas chromatographic analysis of this mixture after trimethylsilylation showed a result that methionine occupied 33.2%, on a molar basis, of the total N-terminal amino acids. Lith...

A NEW APPLICATION OF HOLLOW FIBER SYSTEM TO SUBSTRATE-DEPENDENT TUMORS

A new compact hollow fiber system which may promise suppression of substrate-dependent tumor cells was proposed. This system consists of a hollow fiber dialyzer, ion-exchange columns and a neutralizing injector. By using this system, L-asparagine in bovine blood was eliminated more effectively than by ordinary hemodialysis system. This approach appears advantageous for treatment of the asparagine-dependent cancers of the reticuloendothelial system.