细胞色素c(Cyt c)诱导烟草悬浮细胞(BY-2)凋亡

用不同浓度细胞色素c(Cyt c)诱导继代时间不同的烟草悬浮细胞48 h后观察形态学特征的结果表明,继代培养10和13 d的细胞均在10 mmol·L-1Cyt c时出现最高的细胞凋亡率,而继代5 d的细胞在Cyt c浓度为12.5 mmol·L-1时细胞凋亡的诱导率仍表现上升趋势;DNA电泳检测结果显示凋亡处理的细胞中DNA呈现较明显的DNA梯度.     

蛇苔细胞色素C（Cyt C）的序列分析及功能预测

通过核酸序列比对,在蛇苔cDNA文库中获得细胞色素C（Cyt C）基因序列,并对其编码的蛋白质产物从同源性、氨基酸组成、理化性质、亚细胞位点、结构和功能等进行生物信息学分析和预测。结果表明,该cDNA序列具有完整的开放阅读框（ORF,104—442bp）,推测编码蛋白为112个氨基酸,与向日葵、荞麦、玉米等Cyt C存在着较高的保守性（相似性分别为84％、85％和84％）,同属于细胞色素C超家族;蛇苔CytC蛋白的分子量为11998．7Da,不含信号肽,成熟的CytC起始于Ala2,其活性位点为Cys23、Cys26、His27和Met89;对蛋白质的翻译后修饰预测表明Ala2存在乙酰化修饰,Lys81和Lys95分别进行三甲基赖氨酸修饰。这些特点与其他植物CytC保持一致,表明该基因为蛇苔cyt c基因,在进化上相对保守。     

猪Pitx2c基因4个SNPs的鉴定及其与肉质性状的关联分析

为研究猪Pitx2c基因与肉质性状的关系,在猪Pitx2c基因中共发现了8个SNPs位点,对其中的4个SNPs位点在4个商业猪种及8个中国地方猪种进行了等位基因频率检测,并在大白×梅山猪F2资源家系中进行了性状关联分析.结果显示,位点c.474C〉T（P〈0.01）及c.636C〉T（P〈0.05）与肉色（MCV1）存在显著或极显著相关;位点c.＊37G〉A及c.＊47G〉A与滴水损失（DLR）、系水力（WHC）及肉色（MCV1）均存在显著相关（P〈0.05）.连锁不平衡分析表明,临近的位点两两之间存在连锁不平衡（LD）.单倍型分析显示,存在两种主要单倍型,并且两拷贝的单倍型-CCGG-有利于肉质的改善.     

微生物谷氨酰胺转氨酶催化细胞色素c赖氨酸残基的定点修饰

研究微生物谷氨酰胺转氨酶(mTG)催化细胞色素c(Cytc)的PEG定点修饰的可行性,并优化修饰条件,研究PEG修饰对Cytc性质的影响。将单甲氧基聚乙二醇氨(mPEG-NH_2)与N-苄氧羰基-谷氨酰胺-甘氨酸(CBZ-QG)共价结合制备含谷氨酰胺残基的甲氧基聚乙二醇衍生物(N-苄氧羰基-谷氨酰胺-甘氨酰-单甲氧基聚乙二醇,CBZ-QG-mPEG);mTG分别催化mPEG-NH_2、CBZQG-mPEG(mTG)修饰Cytc,研究酶法定点修饰Cytc残基的可行性;改变酶的用量、温度、反应时间和p H等反应条件优化谷胺酰胺转氨酶催化修饰Cytc的条件。研究结果表明:(1)mPEG-NH_2不能作为mTG的底物修饰Cytc,甲氧基聚乙二醇氨(mPEG-NH_2)分子上引入谷氨酰胺残基后,在mTG的催化作用下了实现Cytc的PEG修饰,而且基于mTG的底物特异性实现了PEG定点修饰Cytc的赖氨酸(Lys)残基;(2)37℃温度下,p H 8.0的溶液中,1mg/ml的mTG催化修饰反应2h是最佳修饰反应条件;(3)化学法PEG修饰Cytc产物复杂,是多种多点修饰产物的混合物,酶法催化PEG修饰Cytc只产生单一产物;(4)与天然Cytc相比,修饰后Cytc的活力、稳定性都有所提高。提出的谷胺酰胺转胺酶催化修饰法解决了蛋白质Lys残基难以定点修饰的难题,拓展了mTG在蛋白质修饰方面的应用。     

黄花棘豆脱水素OoY_2K_4的鉴定及表达分析

该研究以黄花棘豆cDNA为模板,采用同源克隆法,从黄花棘豆转录组数据库中克隆获得1个响应逆境胁迫的胚胎发育晚期丰富蛋白基因,命名为OoY_2K_4;OoY_2K_4基因ORF为786bp,编码261个氨基酸,含有2个保守的Y片段和4个K片段,为典型的Y_2K_4类脱水蛋白亚家族成员;OoY_2K_4蛋白不具有跨膜结构域,不存在信号肽,亲水性极强,含有1个糖基化位点和17个磷酸化位点;亚细胞定位显示,OoY_2K_4蛋白定位于细胞质中。多序列比对发现,OoY_2K_4蛋白与其他物种第二组LEA蛋白(脱水素)序列高度保守;进化树分析显示,该序列与三叶草、蒺藜苜蓿和紫花苜蓿相似度最高,亲缘关系最近。采用qRT-PCR对OoY_2K_4基因在干旱、高盐、低温以及脱落酸、乙烯、赤霉素处理下的表达分析显示,干旱和高盐胁迫可显著诱导OoY_2K_4基因表达,而低温胁迫下基本无变化;激素处理均可诱导OoY_2K_4基因高效表达,其中脱落酸诱导下OoY_2K_4基因表达最显著。研究推测,OoY_2K_4基因可能通过依赖ABA的信号途径参与黄花棘豆对干旱和高盐逆境胁迫的应答反应。     

乳腺癌CDK4/6抑制剂设计策略的生物信息学研究

通过多种生物信息学工具对CDK4/6蛋白质特性进行系统性分析,对这2种蛋白质产生更深入的了解,并以分析结果为基础,提出针对乳腺癌的CDK4/6抑制剂的设计策略。利用三维建模、位点预测、蛋白相互作用网络构建等软件对CDK4/6的蛋白质结构、翻译后修饰位点、蛋白质相互作用关系及其参与的生物学过程、通路等进行预测分析。CDK4/6均具有较为特殊的三级结构,可为其抑制剂的设计提供有利条件;2种蛋白都存在一定数量的蛋白磷酸化位点及O-糖基化位点,但不存在N-糖基化位点;与CDK4/6产生相互作用的蛋白质数量众多,但大部分为CDK蛋白家族成员及CCN蛋白家族成员;GO及KEGG分析结果显示,2种蛋白共同参与p53信号通路及PI3K-Akt信号通路,并在细胞对外界刺激的反应中起到作用。预测及分析结果表明,可通过空间特异性结合、修饰位点抢占及变构、多通路多形式共同抑制等方式对CDK4/6抑制剂进行设计和改造。为该类研究的进一步发展铺垫了理论基础,为探索多元化癌细胞抑制方案提供了新的思路和角度。     

西藏小型猪细胞色素b基因序列的比较

目的对西藏小型猪Cyt b-基因序列进行分析,研究其遗传背景及其与国内家猪的亲缘关系。方法提取西藏小型猪和巴马小型猪、贵州香猪、五指山猪的全基因组DNA,设计引物扩增Cyt b基因,测序后进行碱基序列比对,建立亲缘关系树,分析西藏小型猪的遗传背景。结果西藏小型猪等国内部分品种猪的Cyt b基因序列与欧洲猪相比有14个变异位点;但是西藏小型猪与国内品种猪相比存在两个特殊碱基位点即在420位点T→C转换的同时在883位点存在G→A转换。结论西藏小型猪与巴马小型猪、贵州香猪、五指山猪等国内家猪有很近的亲缘关系。同时进一步证实西藏小型猪群体内存在一定的遗传分化。     

SGTA基因及其蛋白的生物信息学分析

[目的]对SGTA基因及其蛋白的结构和特征进行生物信息学分析,为研究SGTA与肿瘤形成和发展的相关性提供理论基础。[方法]运用生物信息学数据库和软件对SGTA基因的结构、单核苷酸多态性位点(SNP)、SGTA基因与其他基因的相互作用网络、SGTA蛋白的理化性质、二级结构、蛋白结构域、蛋白翻译后修饰、蛋白质之间相互作用网络进行分析。[结果]人SGTA基因有5种可变剪接产物,编码区存在78个SNP位点,其中错义突变31个,无义突变1个。人SGTA蛋白由313个氨基酸组成,是稳定性不高的亲水蛋白,α-螺旋是其主要二级结构元件,属于TRP超家族,预测有3个磷酸化激酶修饰位点和数个潜在泛素化修饰位点。与SGTA存在相互作用的基因和蛋白多数与维持体内蛋白质稳定的分子伴侣功能相关。[结论]SGTA基因及其蛋白的生物信息学分析为进一步实验研究其在肿瘤形成和发展中的地位及调控机制奠定了基础。     

间隔子修饰引物对扩增产物电泳行为的作用初探

目的:初步研究利用C3Spacer间隔子修饰引物对扩增产物电泳行为的影响及作用。方法:选取1个常用短串联重复序列(STR)位点,利用间隔子修饰该位点荧光标记引物,以DNA标准物质为模板进行PCR扩增,记录相应扩增产物DNA片段长度,进行修饰与长度变化的相关性分析。结果:选取STR位点D13S317,分别利用TTTTC3SpacerC3Spacer、TTTTC3Spacer、TTTT修饰R0X标记引物,相应扩增产物长度为182.67±0.05、182.19±0.11和181.6±0.19bp,未进行修饰的对照组引物扩增产物长度为177.09±0.15 bp,产物DNA片段长度随不同修饰基团的修饰发生规律性变化。结论:发现了一种修饰基团,用该基团修饰引物后,可在体外通过PCR反应改变扩增产物等位基因片段的大小,从而在不改变特异性引物信息的前提下使产物发生规律性位移,修饰基团与DNA片段大小呈内在相关性。     

光合细菌2c菌株益生特性的实验研究

目的研究沼泽红假单胞菌2c菌株益生特性。方法利用耐酸、耐胆盐、体外黏附、平板抑菌试验及大鼠摄入2c菌株后在其体内的存活和持续时间实验研究其益生特性。结果pH2.5条件下处理30min及0.5%或0.9%牛胆盐处理对2c菌株活菌数无显著影响(P0.05);2c菌株体外对4株临床致病菌无抑制作用,体外黏附性能一般。2c菌株在大鼠体内存活和持续时间与摄入剂量有关,停止摄入3d后便不能富集出。结论2c菌株具有较好益生特性。     

Quantum chemical investigation of the intra- and intermolecular proton transfer reactions and hydrogen bonding interactions in 4-amino-5-(2-hydroxyphenyl)-2H-1,2,4-triazole-3(4H)-thione

The intramolecular thione-thiol tautomerism and intermolecular double proton transfer reaction of the hydrogen-bonded thione and thiol dimers in the title triazole compound were studied at the B3LYP level of theory using 6?311++G(d,p) basis function. The influence of the solvent on the single and double proton transfer reactions was examined in three solvents (chloroform, methanol and water) using the polarizable continuum model (PCM) approximation. The computational results show that the thione tautomer is the most stable isomer with a very high tautomeric energy barrier both in the gas phase and in solution phase, indicating a quite disfavored process. The solvent effect is found to be sizable with increasing polarity. In the double proton transfer reaction, the thione dimer is found to be more stable than thiol dimer both in the gas phase and in solution phase. The energetic and thermodynamic parameters of the double proton transfer process show that the double proton exchange from thione dimer to thiol dimer is thermodynamically unfavored. However, the exchange from thiol dimer to thione dimer for the gas phase and water phase seems to be feasible with a low barrier height and with a negative value in enthalpy and free energy changes. In addition, the hydrogen bonding interactions were analyzed in the gas phase regarding their geometries and energies. It is found that all complex formations are enthalpically favored, and the stability of the H-bonds comes in the order of S1—H2···N2 > N2—H2···S1 > N3—H3B···O1. Finally, non-linear optical properties were carried out at the same calculation level in the gas phase.

Intramolecular hydrogen bonding: synthesis and crystal structure of nickel(II) and copper(II) complexes of a tetradentate amine oxime

In the reaction of the tetradentate ligand 3,3′-(1,4- butanediyldiamino) bis (3-methyl-2-butanone)-dioxime (BnAO) with nickel(II) and copper(II), the monomeric [Ni(BnAO-H)]I·H₂O and a mixed monomer/dimer salt [Cu(BnAO-H)H₂O]₂[(Cu(BnAO-H))₂](ClO₄)₄, respectively, are formed, and all complexes have an intramolecular hydrogen bond between cis oxime groups. The OHO bonds give the characteristic infrared absorptions as well as the downfield proton-NMR signal (Ni complex). [Ni(BnAO-H)]I·H₂O crystallizes in space group P2₁/a with a=13.511(2), b=10.599(2), c=14.096(2) Å, β=97.52°, Z=4 and D_c=1.623 g/cm³. The structure was solved by Patterson and Fourier methods and refined by full-matrix least-squares techniques to a final R of 0.021 for 2124 reflections with I 2σ(I). The nickel(II) atom in the complex has slightly distorted square planar geometry with an intramolecular O···O contact of 2.417(7) Å. The copper(II) complex crystallizes in space group P2₁/c with a =13.425(2), b=21.446(3), c=14.349(4) Å, β= 104.4(5)°, Z=8 (monomers) and D_c=1.485 g/cm³. The final R value for this complex was 0.053 for 3033 reflections with I 2σ(I). This structure contains a monomeric [Cu(BnAO-H)H₂O]⁺ ion and a dimeric [(Cu(BnAO-H))₂]²⁺ ion, having intramolecular O···O hydrogen bonds of 2.421(5) and 2.531(5) Å, respectively. The copper(II) ions have square-pyramidal coordination with the axial positions occupied by an oxygen of the water of hydration in the monomer and by an oxime oxygen atom in the dimer. A center of symmetry relates the two halves of the dimer. The copper atom in each case is out of the plane of the four nitrogen atoms toward the axial site. The copper(II) complex is unusual in that the crystal contains both a monomer and a dimer.     

Fluorescence studies on concanavalin-A

Using the lectin-concanavalin-A, the tryptophan fluorescence as a function of pH was studied. The pH dependent, fluorescence intensity changes were significantly higher when excited at 305 nm, than when irradiated at 280nm. Only one tryptophanyl per monomer of concanavalin-A was available for oxidation by N-bromosuccinimide in the dimeric form at pH 4·9; no tryptophanyl could be oxidised in the demetallised dimer (pH 3·0) and native tetramer (pH 7·0). Based on this fluorescence data and the already known crystal structure data, it appears that tryptophanyl 88 in concanavalin-A may be selectively excited by 305 nm radiation     

Preliminary crystallographic data for Azotobacter cytochrome c5.

Two closely related crystal forms of dimeric cytochrome c₅ from Azotobacter rinelandii have been grown. The crystals belong to space groups (C2 with $\text{a = 45·0, b = 38·4, c = 41·3}\text{A}\text{?}\text{and}\text{β = 101 ° 0′}$; and C1 (a centered triclinic cell) with $\text{a = 46·0, b = 37·6, c = 49·4}\text{A}\text{?}$, α = 87 ° 20′, β = 96 ° 40′ and γ = 90 ° 0′. In C2 the 24,000 molecular weight dimer lies on a Crystallographic 2-fold axis; in C1 the entire dimer occupies the asymmetric unit.     

Formation of homovanillic acid dimer by enzymatic or Fenton system - catalyzed oxidation

Homovanillic acid is the most extensively employed reagent for the fluorometric detection of peroxidase. However, the assays based on the determination of the oxidation product of homovanillic acid do not allow a selective detection of the enzyme, because chemical or physical factors can interfere with the fluorometric determination. The aim of this work was to verify if other enzymatic or non-enzymatic systems might catalyze the homovanillic acid oxidation. The reaction was investigated by spectrophotometric and fluorometric assays; HPLC analysis was used to separate homovanillic acid from its oxidation product and to obtain information on the oxidation process. The results obtained showed that soybean lipoxygenase in the presence of hydrogen peroxide can oxidize homovanillic acid with the formation, by an o,o'-biphenyl linkage, of the corresponding dimer as the sole reaction product. The reaction followed Michaelis-Menten kinetics, for both homovanillic acid and hydrogen peroxide. Other systems, such as cytochrome c/H(2)O(2) and Fenton reagents, were also able to oxidize homovanillic acid to its dimer. It can be affirmed that possible interference by other oxidative systems - that could be present in the biological materials tested - should be considered in assays of peroxidase activity based on the detection of the dimer of homovanillic acid.     

尿激酶抗人交联纤维蛋白-D-二聚体单抗化学偶合体的制备

利用双功能试剂Ｎ－琥珀酰亚胺－３（２－二硫吡啶）丙酸酯（ＳＰＤＰ）作交联剂,合成了尿激酶（ＵＫ）－抗人交联纤维蛋白降解物Ｄ－二聚体单抗（ＭＡ－ＨＩＤ１）化学偶合体（ＵＫＭＡ－ＨＩＤ１）,并用苯甲脒－Ｓｅｐｈａｒｏｓｅ６Ｂ及人交联纤维蛋白降解物Ｄ－二聚体－Ｓｅｐｈａｒｏｓｅ４Ｂ亲和柱纯化,获得偶合体产物．ＳＤＳ－ＰＡＧＥ呈现一条带,其分子量约为２０００００．纤维蛋白平板法测活结果显示,偶合体中酶比活为５３０００ＩＵ／ｍｇ尿激酶蛋白,与偶联前的５４３００ＩＵ／ｍｇ蛋白相仿．ＥＬＩＳＡ测试显示,偶合体对人交联纤维蛋白降解物Ｄ－二聚体有免疫反应性,并且与偶联前的抗Ｄ－二聚体单抗对此抗原的反应性相当     

Affinity interaction of hydroxypyruvate reductase from Methylophilus spp. with Cibacron blue F3GA-derived poly(HEMA EGDMA) microspheres: partial purification and characterization

A methylotrophic hydroxypyruvate reductase was partially purified and characterized from Methylophilus spp. using the biomimetic dye, Cibacron Blue F3FA attached to poly(HEMA-EGDMA) microspheres. The absorption capacities of the dye-affinity microspheres were determined by changing pH and the concentration of the proteins in the adsorption medium. Hydroxypyruvate reductase was desorbed from the dye-affinity support specifically with 2 mM NADH solution. The enzyme was purified 10·4-fold with 47% yield. The molecular mass and subunit molecular mass of the enzyme was estimated to be 75 kDa and 37 kDa on the basis of its mobility in polyacrylamide and SDS-polyacrylamide gels, respectively. This suggested a homogeneous dimer structure. The optimal pH was between 5·0 and 7·0, and the maximum enzyme activity was obtained at 50°C. The K_m values of hydroxpyruvate reductase were 0·222 mM for hydroxpyruvate and 0·067 mM for NADH.     

Photosynthetic membrane development in Rhodopseudomonas sphaeroides. Spectral and kinetic characterization of redox components of light-driven electron flow in apparent photosynthetic membrane growth initiation sites

The kinetics of light-driven electron flow and the nature of redox centers at apparent photosynthetic membrane growth initiation sites in Rhodopseudomans sphaeroides were compared to those of intracytoplasmic photosynthetic membranes. In sucrose gradients, these membrane growth sites sediment more slowly than intracytoplasmic membrane-derived chromatophores and form an upper pigmented band. Cytochromes c1, c2, b561, and b566 were demonstrated in the upper fraction by redox potentiometry; c-type cytochromes were also detected electrophoretically. Signals characteristic of light-induced reaction center bacteriochlorophyll triplet and photooxidized reaction center bacteriochlorophyll dimer states were observed by EPR spectroscopy but the Rieske iron-sulfur signal of the ubiquinol-cytochrome c2 oxidoreductase was present at a 3-fold reduced level on a reaction center basis in comparison to chromatophores. Flash-induced absorbance measurements of the upper pigmented fraction demonstrated reaction center primary and secondary semiquinone anion acceptor signals, but cytochrome b561 photoreduction and cytochrome c1/c2 reactions occurred at slow rates. This fraction was enriched approximately 2- and 4-fold in total b- and c-type cytochromes, respectively, per reaction center over chromatophores, but photoreducible b-type cytochrome was lower. Measurements of respiratory activity indicated a 1.6-fold higher level of succinate-cytochrome c oxidoreductase/reaction center than in chromatophores, but the apparent turnover rates in both preparations were low. Overall, the results suggest that complete cycles of rapid, light-driven electron flow do not occur merely by introduction of newly synthesized reaction centers into respiratory membrane, but that subsequent synthesis and assembly of appropriate components of the ubiquinol-cytochrome c2 oxidoreductase is required.     

Pregnancy zone protein,a proteinase binding α-macroglobulin. Stopped-flow kinetic studies of its interaction with chymotrypsin

Human pregnancy zone protein (PZP) is a major pregnancy-associated plasma protein, strongly related to α₂-macroglobulin (α₂M). The proteinase binding reaction of PZP is investigated using chymotrypsin as a model enzyme. The time-course of the interaction is studied by measuring the change in intrinsic protein fluorescence of PZP-chymotrypsin reaction mixtures as a function of time after rapid mixing in a stopped-flow apparatus. Titrations show the changes of fluorescence at equilibrium to correspond with the formation of a chymotrypsin-PZP(tetramer) species. The kinetic results show the formation of the species to take place in an overall second-order process dependent on the concentrations of chymotrypsin and of PZP(dimers), k = 5 · 10⁵M⁻¹ ·s⁻¹. Reactions of PZP-thiol groups do not give rise to fluorescence changes. The fluorescence changes most likely reflect the formation of an intermediate with intact thiol esters. Further analysis of the kinetic results suggests that the chymotrypsin-PZP(tetramer) intermediate is formed in two reaction steps: (1) initially native PZP(dimers) are cleaved at bait regions by enzyme molecules, and that is the rate determining reaction of the fluorescence changes; (2) association with another PZP(dimer) or PZP(dimer)-chymotrypsin complex in a very fast reaction that leads to the formation of 1:1-chymotrypsin-PZP(tetramer) intermediate, probably with intact thiol esters. The interactions studied apparently are established early in the path of the reaction and the fluorescence changes probably reflect noncovalent enzyme-PZP contacts, which are not changed when covalent binding occurs. Further, fluorescence changes are seen only in reactions of PZP with enzymes, not with methylamine.     

The development of SS''-polymethylenebis(methanethiosulphonates) as reversible cross-linking reagents for thiol groups and their use to form stable catalytically active cross-linked dimers within glyceraldehyde 3-phosphate dehydrogenase.

The synthesis of a series of SS'-polymethylenebis(methanethiosulphonates) including the pentane, hexane, octane, decane and dodecane derivatives is described. These derivatives were synthesized by condensation between dibromoalkanes and potassium methanethiosulphonate in refluxing methanol and this seems an especially versatile reaction for the synthesis of asymmetric thiosulphonate derivatives. The synthesis of SS'-[1,8-3H4]-octamethylenebis(methanethiosulphonate) was also perfomed. Cross-linking was demonstrated in the four enzymes lactate dehydrogenase, phosphofructokinase, pyruvate kinase and glyceraldehyde 3-phosphate dehydrogenase. For all four enzymes cross-linking was efficiently reversed by reducing conditions in denaturing solvents. The reaction with glyceraldehyde 3-phosphate dehydrogenase was unique in that only the cross-linked dimer was produced in significant amounts (greater than 90% of total products as dimer). This reaction was followed in detail with radioactive cross-linking reagent. Inhibition of enzyme activity was extremely fast and showed an asymmetric distribution of enzyme activity on subunits. Thus complete modification of only one subunit resulted in up to 75% inhibition of enzyme activity. Reaction of glyceraldehyde 3-phosphate dehydrogenase with 1.25 mol of SS'-octamethylenebis(methanethiosulphonate) per mol of enzyme subunit produced two species of protein. The first species was obtained in 20% yield and was only partially re-activated on mild reduction with 2-mercaptoethanol. The second species was isolated in 66% yield and was completely re-activated on mild reduction. Before reduction there was 4 mol of inhibitor per tetramer for the latter species, and more than 95% of the enzyme was present as a dimer on non-reducing electrophoresis. After mild reduction 2 mol of inhibitor was still bound per tetramer, the enzyme was now catalytically active and the dimer was still the major structure on non-reducing electrophoresis. Thus mild reduction of SS'-octamethylenebis(methanethiosulphonate-treated glyceraldehyde 3-phosphate dehydrogenase enabled the production of active enzyme in which there is a stable cross-link across one of the molecular axes of the tetrameric enzyme. This cross-link was only reversed if reduction was performed when the enzyme was denatured. The molecular weight of cross-linked and re-activated cross-linked glyceraldehyde 3-phosphate dehydrogenase was established as 144000 (tetramer) by sucrose-density-gradient centrifugation. These observations are interpreted in terms of the molecular structure of glyceraldehyde 3-phosphate dehydrogenase.