Biochemical Studies on Rice Bran Lipase

Some chemical properties of the rice bran lipase were studied. The enzyme protein contained 14.98% nitrogen and consisted of 312 amino acid residues. It also contained a certain amount of lipid. The amino-terminal amino acids of the enzyme protein were shown to be glutamic acid and the carboxyl-terminal amino acids to be glycine and serine. The treatment of the enzyme protein with 8 m urea containing 1×10^?3m EDTA (ethyl-enediaminetetraacetic acid) seemed to cause dissociation of the subunits of the enzyme protein. From this observation and the results of the terminal amino acids analysis, it was presumed that the enzyme protein was composed of at least two types of subunits.     

Studies on Biochemistry of the Thiobacilli

In the oxidation of thiosulfate at pH 4.5 tetrathionate was formed as an intermediate, and the thiosulfate-oxidizing enzyme was active in acidic pH range in contrast to the enzyme of T. thioparus and Thiobacillus X.

Phosphate did not seem to affect the oxidation of thiosulfate but rather affect the conversion of tetrathionate. In the absence of phosphate, tetrathionate, which was produced from thiosulfate oxidation, seemed to accumulate without undergoing further conversion.

Quantitative oxidation of tetrathionate to sulfate was achieved with freshly harvested cells of T. thiooxidans; pH optimum for the oxidation of tetrathionate by the washed cells was 2~3, and the activity fell markedly at pH above 3.5.

Tetrathionate might be enzymatically dismuted to pentathionate and trithionate under anaerobic conditions with crude extracts of T. thiooxidans; pH optimum for the reaction was about 2.7 and the activity fell strikingly at pH 4.7. The formed trithionate might be further hydrolyzed to thiosulfate and sulfate.     

Studies on the Flavors of Roast Barley (Mugi-Cha)

Five weakly acidic carbonyl compounds and two neutral carbonyl compounds were newly isolated as their 2,4-dinitrophenylhydrazones besides the previously reported compounds by using column and thin-layer chromatographies.

These compounds were characterized and identified by their IR, UV and MS spectra and the mixed melting points test.

The newly isolated and identified compounds were as follows; weakly acidic carbonyl compounds: 2-pyrrolealdehyde, vanillin, p-hydroxybenzaldehyde, syringaldehyde, proto-catechuic aldehyde, neutral carbonyl compounds: glyoxal, 5-hydroxymethylfurfural.

These compounds, particularly vanillin, protocatechuic aldehyde, 2-pyrrolealdehyde and 5-hydroxymethylfurfural, appeared to be concerned with the flavor of roast barley (Mugi-Cha).     

Influence of Protein Source on Growth-depressing Effect of Excess Amino Acids in Young Rats

The influence of protein quality on the growth-depressing effect of excessive amount of 12 individual essential and semiessential amino acids was examined. Growing rats were fed for 3 weeks diets containing either 10.5% egg albumin or 11.6% wheat gluten (equivalent to the protein content of a 10% casein diet) supplemented with 5% of each of the l-amino acids. In general, the pattern of growth depression produced by the addition of excess amino acids to the egg albumin or the wheat gluten diet was similar to that of the case of casein diet obtained previously under the same experimental conditions. However, the extent of these effects was dependent not only upon the kind of amino acid supplemented with but also upon the source of protein used, and the depressing effect of each of excess amino acids added to the wheat gluten diet was usually severer than those added to casein and egg albumin diets. No evidence was noted of any striking changes in the liver protein and nucleic acid concentrations by either diets, but total liver protein, RNA and DNA contents were decreased in some amino acid groups of the egg albumin diet and in all amino acid groups of the wheat gluten diet except the lysine addition. The free amino acid level in plasma generally showed extreme elevation for the amino acid supplemented in excess in the diet, and in most cases the extent of the elevation was correlated with the growth depression.     

Edge-related changes in tree communities in the understory of mesic temperate forest fragments of northern Japan

We have assessed the effects of habitat fragmentation on understory tree communities in mesic temperate forests of the Tokachi plain of northern Japan. Tree community composition was analyzed across 13 forest fragments of various sizes ranging from 0.30 to 8.51 ha. The community composition varied along the edge-to-interior gradient: there was a lower abundance of shade-tolerant shrubs in forest edges than in forest interiors, while saplings of dominant canopy trees and pioneer trees were more abundant near the edges. The edge influence extended approximately 56 m into the forest interiors. Even the interior area of small fragments were likely to be affected not only by the nearest edge but also by more distant edges. Consequently, most areas in fragments smaller than 2 ha were covered by these “edge-type” communities. These results indicate that it is of primary importance to conserve and restore forests with an area at least larger than several hectares to sustain forest-interior tree communities.     

The Structure-taste Relationships of Aspartyl Dipeptide Esters

The molecular features common to sweet-tasting dipeptide esters are described. The molecular features of sweet amino acids were represented by the Fischer projection formulas and sweet peptides were related to the sweet amino acids through the Fischer projection formulas of the peptides. It was concluded that a peptide is sweet when it takes the formula 5a, whereas when it takes the formula 5b it is not sweet. It was also concluded that a third binding site (R₁ in 5a) besides the postulated AH–B system in a sweet molecule is necessary for an intense sweetness potency. The location of the site in the molecule relative to the AH–B system is important, as well as the shape and size of this site, because the third binding site is considered to participate in hydrophobic interaction with a similar binding site on the taste receptor. Increased sweetness is observed when these requirements are satisfied.     

Microbial Reduction of 1,2-Diketones to Optically Active α-Hydroxyketones

We have attempted to develop an intraoral method which can measure the textural changes in foodstuffs during chewing by using electromyography (EMG). Forty-three foodstuffs with variable textural attributes were used.

Total chewing energy for these foodstuffs during chewing varied from 3 to 108 for the masseter muscle and 13 to 154 for the digastric muscle, respectively. Large differences in total chewing energy could be observed by EMG among the foodstuffs. The chewing energy for many foodstuffs revealed distinct differences throughout the chewing process. Foodstuffs could be categorized into six groups according to the changing patterns of chewing energy. EMG data and the number of strokes were influenced by masticatory index and salivary flow rate.     

Gelation and Its Related Changes in Amylose Solution

The phase change for an amylose solution in the binary solvent system of dimethylsulfoxide (DMSO) with water was investigated under various conditions from sol to gel. The phase change was determined with measurements of the fluorescent depolarization and other methods by varying the solvent constitution at 25°C, and then varying the temperature at 10% of DMSO concentration.

The phase diagrams obtained with both variables were substantially similar and were also similar to those for an aqueous agarose solution. This similarity in phase diagram suggests a similar gel formation mechanism of amylose to agarose.

It was found that the phase separation point for the amylose solution agreed with the gel formation point and also with the starting point of retrogradation.