Shunichi Dosako

Lactoperoxidase suppresses acid production in yoghurt during storage under refrigeration

Abstract Three types of fermented milk were prepared using either Lactobacillus bulgaricus, Streptococcus thermophilus , or their mixed culture. Five mgkg −1 of lactoperoxidase (LPO) suppressed acid production in the yoghurts during refrigerated storage. The most effective suppression was observed with the mixed starter culture. Addition of LPO did not affect the incubation time at 41 °C except for the L. bulgaricus single culture. While the viable cell counts of the single cultures were constant during storage, with or without the addition of LPO, the viable cell counts of L. bulgaricus in the mixed culture decreased in the presence of LPO. A significant decrease in LPO activity was observed during incubation. The concentration of thiocyanate in LPO-treated yoghurt was lower than that in the control by 2–3 mg kg −1 . The addition of LPO produced a new type of yoghurt which retains acceptable quality during storage for at least two weeks.

Amino Acid Residue Substitution at T-Cell Determinant-flanking Sites in β-Lactoglobulin Modulates Antigen Presentation to T Cells through Subtle Conformational Change

We compared T-cell responses to regions in residues 21-40 of A and B variants of bovine milk β-lactoglobulin (β-LG) that vary by two different amino acid residues at 64 and 118. Results showed that T cells from C57/BL6 and C3H/HeN mice immunized with peptide 21-40 or BALB/c mice immunized with peptide 21-32 or 25-40 responded more vigorously to β-LG B than to β-LG A. This difference in response to 25-40 in BALB/c mice was not observed when β-LGs B and A were denatured, suggesting that the conformation difference affects display of the determinant 25-40. Reactivity of anti-β-LG monoclonal antibodies and molecular modeling using molecular dynamics calculations revealed subtle differences in the three-dimensional structure of these two variants. Furthermore, substitution of two amino acid residues at sites distant from the T-cell determinant induced differential determinant display on antigen-presenting cells, possibly due to subtle conformational changes in β-LG.

Long term culture of mouse hybridoma HB8852 cells in a protein free medium

SummaryWe developed a protein free medium based on ERDF medium containing 80 μM FeSO4, ethanolamine and selenite. Although this medium contained neither transferrin nor insulin, the medium could support long term culture of mouse hybridoma HB8852 without any significant changes in antibody production.

Generation of hybrid hybridomas secreting human IgM class hybrid antiricin and antidiphtheria toxin antibodies

Two lines of mouse-human hybridomas were fused to produce human bifunctional antibodies. A hybridoma that secretes human IgM (kappa) class antiricin monoclonal antibody was treated with actinomycin D to inhibit cell growth. Another cell line, secreting human IgM (lambda) class antidiphtheria toxin monoclonal antibody, was 6-thioguanine resistant (HAT sensitive). Six hybridomas secreting IgM with both kappa and lambda light chains were obtained. Two of them secreted antibodies with antiricin specificity (kappa and lambda light chains) and antidiphtheria toxin specificity (kappa and lambda light chains). Antidiphtheria toxin antibodies secreted from other hybrid hybridomas did not contain kappa light chain, but lambda chain. A hybrid hybridoma clone 5-29 secreted complete hybrid IgM with lowered affinity to diphtheria toxin. These results suggested unbalanced recombination of immunoglobulin polypeptide chains in hybrid hybridomas.

Adaptation of mouse-human hybridomas to a protein free medium

SummaryFive mouse-human hybridoma cell lines secreting human IgM class monoclonal antibodies were examined for possible adaptation to a protein free medium. Four were successfully adapted to the medium. The adapted cell lines could be cultured for more than two months without any changes in their cell growth abilities.

Human hybrid immunoglobulin M containing immunoglobulin A

SummarySome hybridoma clones made by fusion of a human lymphoblastoid cell line, HO323 with human B lymphocytes, secreted not only IgA but also IgM-like immunoglobulin molecules. The IgM-like immunoglobulin had a molecular size of 900 K which corresponded to that of IgM. Immunochemical analyses revealed that the IgM-like immunoglobulin contained two monomeric IgA and three monomeric IgM molecules. In the IgA moieties, half of original light chains were replaced withx chains derived from the IgM, and vice versa.

Purification and some properties of proliferation suppressing factor from human lung adeno carcinoma PC-8

Extracts by 3 M KCl from a human lung adenocarcinoma cell line, PC-8, suppressed the proliferation of phytohemagglutinin activated lymphocytes. The proliferation suppressing facfor (PSF) was purified from the extracts by ammonium sulfate precipitation, gel filtration and ion exchange chromatography. The purified PSF had a molecular weight of 50 kDa by SDS-PAGE and was acid-and heat-labile. Since the PSF also suppressed the proliferation of three established human cell lines, it is unlikely that the PSF hinders the interaction between lymphocytes and mitogens.

Fluorescence Polarization of αs1, κ-Caseins and αs1-κ-Casein Complex

Conjugates of αs1-,κ-caseins and αs1-,κ-casein complex were prepared with dimethylaminonaphthalenesulfonate and pyrenebutyrate. Their fluorescence lifetimes and the rotational relaxation times were measured by single photon counting technique and fluorescence depolarization technique, respectively. Both dimethylaminonaphthalenesulfonate and pyrenebutyrate conjugates had more than two lifetimes and the longer lifetime of pyrenebutyrate conjugates was near 140 nsec.The rotational relaxation time of pyrenebutyrate αs1-,κ-casein complex was smaller than that of pyrenebutyrate κ-casein polymer, which suggested that the complex formation of αs1- and κ-casein polymers led to dissociation of the κ-casein polymer.Changes of the rotational relaxation time as a function of weight ratio of αs1- and κ-casein polymers (αs1/κ) showed the specific variation and it was suggested that 4 moles of αs1-κ-casein complex were formed from one mole of κ-casein polymer.

Prevention from Hardening of Fibrous Soybean Protein

繊維状大豆蛋白質を凍結保存し, 解凍後調理冷凍食品などに加工すると硬さを増加する。この変化を繊維状大豆蛋白質製造時に防止し得る工程を見い出す目的で若干の検討を行った。因子として, リン酸緩衝液浸漬の有無, 食塩水浸漬の有無, ソルビトールコーテングの有無, ラードコーテングの有無および凍結速度を選び, 直交表L16による実験を行い繊維状大豆蛋白質の切断力を測定した。その結果, リン酸緩衝液あるいは食塩水浸漬, およびソルビトールコーテングが切断力を有意に低下させた。また, 急速と緩慢凍結の間では, 切断力を低下させた上記処理を行わなければ, 急速凍結の方が低い切断力を示す傾向にあったが, これらの処理を行うと両者に有意差を認めなかった。更に, 切断力を小さくする最適工程条件を推定し, リン酸緩衝液あるいは食塩水に浸漬した後にソルビトールをコーテングすれば, 緩慢凍結を行っても繊維状大豆蛋白質が硬くなる変化を有意に防止し得ることが推察された。この条件下では, 何ら防止処理を行わない時に比較し, 切断力は約55%となることが推定された。