ADA2 isoform of adenosine deaminase from pleural fluid

Adenosine deaminase isoenzyme 2 (ADA2) was isolated from human pleural fluid for the first time. Molecular and kinetic properties were characterized. It was shown that the inhibitors of adenosine deaminase isoenzyme 1 (ADA1), adenosine, and erithro-9-(2-hydroxy-3-nonyl)adenine (EHNA) derivatives are poor inhibitors of ADA2. Comparison of the interaction of ADA2 and ADA1 with adenosine and its derivative, 1-deazaadenosine, indicates that the isoenzymes have similar active centers. The absence of ADA2 inhibition by EHNA is evidence of a difference of these active centers in a close environment. The possible role of Zn2+ ions and the participation of acidic amino acids Glu and Asp in adenosine deamination catalyzed by ADA2 were shown.     

Bioconversion of phospholipids by immobilized phospholipase A2

Phospholipase A₂ selectively hydrolyses the ester linkage at the sn-2 position of phospholipids forming lysocompounds. This bioconversion has importance in biotechnology since lysophospholipids are strong bioemulsifiers. The aim of the present work was to study the kinetic behaviour and properties of immobilized phospholipase A₂ from bee venom adsorbed into an ion exchange support. The enzyme had high affinity for CM-Sephadex^® support and the non-covalent interaction was optimum at pH 8. The activity of immobilized phospholipase A₂ was comparatively evaluated with the soluble enzyme using a phospholipid/Triton X-100 mixed micelle as assay system. The immobilized enzyme showed high retention activity and excellent stability under storage. The activity of the immobilized system remained almost constant after several cycles of hydrolysis. Immobilized phospholipase A₂ was less sensitive to pH changes compared to soluble form. The kinetic parameters obtained (V_max 883.4 μmol mg⁻¹ min⁻¹ and a K_m 12.9 mM for soluble form and V_max = 306 μmol mg⁻¹ min⁻¹ and a K_m = 3.9 for immobilized phospholipase A₂) were in agreement with the immobilization effect. The results obtained with CM-Sephadex^®-phospholipase A₂ system give a good framework for the development of a continuous phospholipid bioconversion process.     

商品果胶酶中endo－PG的分离纯化及其部分性质研究

以Ａ．ｎｉｇｅｒ来源的果胶酶为材料,经过ＣＭ－ＳｅｐｈａｄｅｘＣ－５０及ＳｅｐｈａｄｅｘＧ－１００两步骤分离纯化得到电泳均一的ｅｎｄｏ－ＰＧ１及ｅｎｄｏ－ＰＧ２,其亚基分子量分别为３５ｋＤ及３７ｋＤ,含糖量为１１．２２％及８．３％,最大紫外吸收峰分别在２７４ｎｍ及２６９ｎｍ处,氨基酸组成分析结果表明Ｇｌｙ含量较高,Ｍｅｔ含量较低,不含Ｃｙｓ,并且酸性氨基酸含量高于碱性氨基酸,圆二色谱结果表明二级结构主要为α螺旋和β折叠,其中ｅｎｄｏ－ＰＧ１含α螺旋４５．１％,β折叠２４．９％;ｅｎｄｏ－ＰＧ２含α螺旋３９．６％,β折叠３６．５％。