Danji Fukushima

Recent progress of soybean protein foods: chemistry, technology, and nutrition

Abstract The most important chemical reactions during the process of soybean protein foods are the intermolecular reactions among the residues exposed on the surface of the protein molecules through the denaturation process. In native soybean protein molecules, most amino acid residues responsible for the reactions—such as cysteine (‐SH), cystine (S‐S), and hydrophobic amino acid residues—are buried in the inside region of the molecule, inaccessible to water. These residues become reactable with each other through the exposure from the inside by heat denaturation during processing. The unique textures of soybean protein foods, such as tofu, kori‐tofu, yuba, and texturized products produced by extruder, etc., are the results of both the intermolecular interchange reaction between the exposed ‐SH and S‐S groups and the intermolecular hydrophobic reaction among the exposed hydrophobic amino acid residues. The exposure of amino acid residues is also important for the hydrolysis of soybean proteins by enzymes,...

Structures of plant storage proteins and their functions

Abstract The complete amino acid sequence of plant storage protein molecules has been determined over the past decade by sequence analysis of full‐length cDNA and genomic clones for most cereal and legume seeds. At the same time, knowledge on the biosynthesis of the storage proteins has also been accumulated at the molecular level. According to the data on the gene structures of the plant storage proteins, the homology of their amino acid sequences, and the mechanisms of their accumulation into the protein bodies in the biosynthesis, the storage proteins which are classified as glutelins by a traditional sequential extraction method should be classified as either globulins or prolamins on the basis of the molecular structures. For instance, both orizenin, the rice main storage protein, and glutenin, the most important protein component of wheat proteins, have been classified as glutelins, but they should be classified as globulins and prolamins from the molecular base standpoint, respectively. The amino a...

A new enzyme, proline acylase (N-acyl-l-proline amidohydrolase) from Pseudomonas species

Abstract A new enzyme, proline acylase, extracted from a strain of Pseudomonas species has been purified to apparent homogeneity and has been shown to hydrolyze specifically N- acyl - l - proline derivatives such as N- acetyl - l - proline and chloroacetyl- l -proline. N -Acetylamino acids other than l -proline were unsusceptible, or nearly so. The enzyme also hydrolyzed the carboxyterminal proline residue in a peptide when its penultimate position was occupied by a glycine, such as Z-Gly- l Pro and Z-Gly- l Pro- l Leu-Gly- l Pro. It has a pH optimum at pH 6.0 and was inhibited by chelating reagent. The molecular weight was estimated to be 597 000 and 623 000 by sedimentation equilibrium and gel filtration, respectively. Upon disc electrophoresis in 1% SDS, the purified preparation migrates as a single band of molecular weight 55 000. The sedimentation coefficient and isoelectric point, determined by polyacrylamide gel electrophoresis, were s 20, w 0 = 18 S and pH = 5.0, respectively.

Oxidative Browning of Amadori Compounds from Amino Acids and Peptides

The oxygen-dependent browning (oxidative browning) of Amadori compounds from amino acids or peptides was studied since it was an important reaction contributing to the discoloration and deterioration of some foodstuffs containing sugars and amino compounds during storage in contact with atmospheric oxygen.

Conformational Changes of Aspergillus sojae Alkaline Proteinase with Denaturing Reagents

The conformational changes of the alkaline proteinase of Aspergillus sojae were analyzed, after the treatments with urea and guanidine hydrochloride, by the optical rotatory dispersion, Cotton effects, ultraviolet difference spectra, and viscosity measurements. The results are as follows; (1) The treatment with 8M urea (pH 7.0) seemed to cause at least two different conformational changes assumed from the changes in the Moffitt parameter, a0. One is a rapid and reversible change and the other is a gradual and irreversible change. During the process of the later change, it was observed that the complete disruption of the α-helices assumed from the b0 value and the Cotton trough at 233mμ proceeded in parallel with the loss of enzymatic activity. (2) The conformational change after the treatment with 1.6M guanidine hydrochloride (pH 7.0) was considered to be rather small, judging from the changes in the a0 value and intrinsic viscosity. However, by this treatment, the two tryptophan residues which are buried in the interior of the molecule were exposed to the solvent, the α-helices were completely disrupted, and the enzymatic activity was completely lost.