核酸酶P_1固定化研究

利用正交试验法对钛氯活化纤维素固定核酸酶Ｐ_１的工艺条件进行优化，获得了较优的固定化工艺条件，酶活力回收提高到８４．５％，降解酵母ＲＮＡ的５＇－核苷酸生成率平均可达７４．２％。     

Contents of amino acids,organic acids and 5′-nucleotides in Tricholoma giganteum

Tricholoma giganteum fruiting-bodies ere collected in a grassy place in Amami Oshima (Kagoshima Pref.) in October 1988 and the quantitative difference of 5′-nucleotides, free amino acids and organic acids, hich are responsible for the taste of dried mushrooms ere investigated. The amount of 5′-CMP, 5′-AMP, 5′-UMP and 5′-GMP ere 1250, 637, 863 and 566 mg kg^?1 respectively. 5′-GMP amounted to 17.1% of the total 5′-nucleotides. In the amino and organic acids, alanine, glutamic acid, serine, aspartic acid, succinic acid, oxalic acid and acetic acid ere present in the largest amounts.     

A novel selective nucleoside phosphorylating enzyme from Morganella morganii

A selective nucleoside phosphorylating enzyme was purified to homogeneity from Morganella morganii NCIMB10466 crude extract. The enzyme appeared to consist of six subunits identical in molecular mass (M_r 25,000). It phosphorylated various nucleosides at the 5′-position to produce nucleoside-5′-monophosphates using pyrophosphate as the phosphate source. Energy-rich compounds, such as carbamylphosphate and acetylphosphate, were also very effective phosphate donors. The enzyme also exhibited phosphatase activity, and dephosphorylated various phosphate esters, but had a weak effect on nucleoside-3′-monophosphates. Based on the results of the kinetic study, the enzyme appeared to be an acid phosphatase. Its activity was partly inhibited by sulfhydryl reagents and heavy metal ions, but not by chelating reagents such as EDTA. Using the purified enzyme, 32.6 mM 5′-IMP was synthesized from inosine with a 41% molar yield, but the synthesized 5′-IMP was hydrolyzed back to inosine and phosphate as the reaction time was extended.     

5＇-磷酸二酯酶强化香菇风味基料中鲜味成分

研究了5＇-磷酸二酯酶强化香菇鲜味成分的工艺条件及其作用.在香菇打浆料中添加5＇-磷酸二酯酶及酵母粉,研究各因素对5＇-核苷酸产量的影响.结果表明,酵母粉用量、5＇-磷酸二酯酶用量、酶解体系pH值、酶解温度及时间等因素对鲜味核苷酸生成有重要影响,正交试验优化的酶解工艺条件为：酵母粉用量5%,5＇-磷酸二酯酶用量5%,pH值4.0,酶解温度60℃,酶解时间60min.在此条件下制备的香菇风味基料中鲜味核苷酸（5＇-IMP、5＇-GMP）产量达到30.01 mg/g,较未经5＇-磷酸二酯酶处理基料的鲜味核苷酸产量提高了3倍.     

Antinutritional effects and ecological significance of dietary condensed tannins may not be due to binding and inhibiting digestive enzymes

The digestive enzymes alkaline phosphatase and 5-nucleotide phosphodiesterase, solubilized from bovine intestinal mucosa and purified to homogeneity, were found to be strongly inhibited in vitro by condensed tannins (proanthocyanidins) purified from sorghum seeds and from quebracho. Tannin inhibition was prevented and reversed by the detergent Triton X-100 (protein-binding agent), by soluble polyvinylpyrrolidone (tannin-binding agent), or by phosphatidylcholine (membrane component). When tested as a crude particulate membrane fraction more characteristic of their in vivo condition, both enzymes were inhibited much less than either purified enzyme at the same tannin concentration. Because the enzymes appear to be relatively insensitive to inhibition by tannin in conditions which mimic in vivo conditions, and because the proportion of the dietary tannin which is available to interact with these enzymes in the digestive tract is likely to be rather small, we suggest that the antinutritional effects and ecological significance of dietary tannins are not due to tannin inhibition of these or other digestive enzymes by direct binding to them.