Hiromichi Kato

Taste of free amino acids and peptides

Abstract Although much attention has been given to olfaction, little attention has been given to taste. It is generally assumed that there are five primary tastes: sweetness, sourness, saltiness, bitterness, and umami. Free amino acids and peptides play important roles eliciting characteristic tastes of foods. In this paper, some tastes of free amino acids and some peptides are discussed.

Mode of degradation of myofibrillar proteins by an endogenous protease, cathepsin L

The mode of degradation of myofibrils and their constituent proteins by cathepsin L (EC 3.4.22.15) of rabbit skeletal muscle was studied. Sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis showed that cathepsin L degraded myosin heavy chain, alpha-actinin, actin, troponin T and troponin I assembled in myofibrils and produced mainly fragments of 160 000 and 30 000 daltons in the acidic pH region. This degradation was most intense around pH 4. Degradation of myosin in the isolated state by cathepsin L resulted in the disappearance of the heavy chain and the decrease of light chains 1, 2 and 3, producing fragments of 160 000, 92 000, 83 000 and 60 000 daltons. The degradation of the heavy chain was most severe at pH 4.2. Cathepsin L degraded actin into fragments of 40 000, 37 000 and 30 000 daltons. This action was most intense at pH 4.7. Tropomyosin was not degraded. Troponin T and troponin I were degraded into fragments of 30 000 and 13 000 daltons at pH 3.7--6.7, which were degraded further into smaller fragments. Troponin C was not degraded. alpha-Actinin was degraded into several fragments, the major one of which showed an Mr of 80 000. This degradation was most intense at pH 3.0--3.5.

METABOLISM OF 3-DEOXYGLUCOSONE, AN INTERMEDIATE COMPOUND IN THE MAILLARD REACTION, ADMINISTERED ORALLY OR INTRAVENOUSLY TO RATS

The Amadori rearrangement compound, the product in the early step of the Maillard reaction of proteins with glucose, is known to be degraded into 3-deoxyglucosone (3DG), a 2-oxoaldehyde. In order to elucidate the metabolic pathway of 3DG, [14C]3DG was synthesized from [14C]-glucose and administered to rats orally and intravenously. 2 h after oral administration of [14C]3DG, the percentages of radioactivity (RaI%) in stomach, small intestine and urine were 3.9, 60 and 6.4%, respectively, while RaI% in liver, kidney, spleen, blood and CO2 were less than 0.5%. The absorption rate of 3DG was obviously lower in comparison with that of glucose. 3 h after intravenous administration of [14C]3DG, the RaI% in urine was 72% and those in liver, kidney, spleen, blood and CO2 were less than 1%. It therefore appeared that the absorbed 3DG was not biologically utilized by the rats, but was rapidly excreted in the urine. Some metabolites of [14C]3DG were detected in urine by TLC-autoradiography. The main metabolite was purified and identified as 3-deoxyfructose by FD-MS and 13C-NMR spectroscopy, indicating that the aldehyde group of 3DG was reduced to an alcohol.

Scavenging of Active Oxygen Species by Glycated Proteins

Scavenging of active oxygen species by glycated proteins was investigated. Glycated proteins were prepared from bovine serum albumin (BSA), insulin, and lysozyme incubated with glucose. Glycated BSA at concentration of 0.5% scavenged 34% of hydroxyl radicals by ESR experiments using DMPO as a spin-trapping reagent. The ability to scavenge hydroxyl radicals by glycated BSA was higher than that by BSA. Hydrogen peroxides also were largely scavenged with an increase in the concentration of glycated proteins. However, the ability to scavenge superoxides by glycated BSA was lower than that by BSA because glycated proteins produced superoxides. Experiments using model compounds such as Amadori compound and caproyl pyrraline suggested that the scavenging ability of glycated proteins against hydroxyl radicals depends on Maillard reaction products in the advanced stage, while the ability against hydrogen peroxides is dependent upon Maillard reaction products in the early stage and brown pigments.

Purification of cathepsin D from rabbit skeletal muscle and its action towards myofibrils

Cathepsin D (EC 3.4.23.4) was purified from rabbit skeletal muscle using acetone-dried muscle powder as starting material. After the acetone-dried powder was extracted with 0.2 mM ATP, the extract was fractionated with acetone an subjected to DEAE-Sephadex A-50 and Sephadex G-100 column chromatography. Rechromatography on a Sephadex G-100 column resulted in a purified preparation. SDS-polyacrylamide gel electrophoresis of the purified enzyme showed one major band of 42,000 daltons and some bands of contaminants. Since gel filtration also indicated a value of 42,000 daltons for the enzyme, it was concluded that muscle cathepsin D has no subunit structure. The enzyme acted optimally towards myofibrils around pH3, resulting in the degradation of the myosin heavy chain and production of a 30,000-dalton component.

Desmutagenic effect of α-dicarbonyl and α-hydroxycarbonyl compounds against mutagenic heterocyclic amines

Abstract The desmutagenic effects of α-hydroxycarbonyl compounds, such as glyceraldehyde, glycolaldehyde, dihydroxyacetone, furtural, 5-hydroxymethylfurfural, maltol, acetol and acetoin and α-dicarbonyl compounds, such as diacetyl, glyoxal, methyl glyoxal and 2,3-pentanedione were investigated against the mutagenic heterocyclic amines, such as Trp-P-1, Trp-P-2, Glu-P-2 and IQ. Most of the carbonyl compounds suppressed the mutagenicity of heterocyclic amines for S. typhimurium TA98, α-dicarbonyl compounds showing a higher desmutagenic effect than α-hydroxycarbonyl compounds. Among the α-hydroxycarbonyl compounds, glyceraldehyde, glycolaldehyde and dihydroxyacetone showed more effective desmutagenicity, and diacetyl among the α-dicarbonyl compounds had the highest desmutagenic effect. These carbonyl compounds alone also showed mutagenecity to S. typhimurium TA100 without S9 mix. The reaction of carbonyl compounds with mutagenic heterocyclic amines also eliminated the mutagenicity of the former for S. typhimurium TA100.

Mode of degradation of myofibrillar proteins by rabbit muscle cathepsin D

The mode of degradation of myofibrillar proteins by the action of highly purified rabbit muscle cathepsin D (EC 3.4.23.5) was studied using SDS-polyacrylamide gel electrophoresis. Cathepsin D optimally degraded myosin heavy chain, alpha-actinin, tropomyosin, troponin T and troponin I at around pH 3. It did not degrade actin or troponin C. Degradation of myosin heavy chain produced four major fragments of 155000, 130000, 110000 and 90000 daltons. Troponin T was hydrolyzed to 33000-, and 20000- and 11000-dalton fragments. Troponin I was degraded into fragments of 13000 and 11000 daltons. Degradation of alpha-actinin and tropomyosin was not as rapid as that of myosin and troponins T and I. Tropomyosin gave a fragment of 30000 daltons, but alpha-actinin showed no distinct band of this fragment on gels.

Changes of volatile components of tomato fruits during ripening

Abstract Volatile components obtained by simultaneous steam distillation-extraction from two varieties of tomato fruits at various ripening stages and their artificially ripened tomato fruits were analyzed by GC and GC-MS using a glass capillary column. One hundred and thirty compounds were identified. Of these, quantitative changes in the major thirty-six compounds were investigated. Hexanal, trans -2-hexenal, 2- iso -butylthiazole, 2-methyl-2-hepten-6-one, geranylacetone and farnesylacetone, which were estimated to be important volatile components of fresh tomato aroma by the GC-Sniff method, increased with natural and artificial ripening. However, many volatile components showed complicated changes in the case of artificially ripened tomato fruits.

Purification of α-ketoaldehyde dehydrogenase from the human liver and its possible significance in the control of glycation

Alfa-ketoaldehyde dehydrogenase, which was extracted and purified from human livers, may act on carbonyl compounds, such as 3-deoxyglucosone, and be involved in the control of glycation (Maillard reaction) in the body.

Morphological changes in myofibrils and glycerinated muscle fibers on treatment with cathepsins D and L.

Morphological changes in myofibrils and glycerinated muscle fibers on treatment with cathepsins D and L obtained from rabbit skeletal muscle were studied by phase contrast and electron microscopy. Cathepsin D degraded the Z-line and filaments adjacent to the H-zone. Cathepsin L caused the fragmentation of myofibrils, and degraded the Z-line and M-line. Both cathepsins induced disturbance of the lateral arrangement of myofibrils.