人体胆汁液晶光学性质的研究

在单偏光和正交偏光显微镜下对人体胆汁液晶的光学性质进行研究。结果表明：人体胆汁中的液晶以球形的微粒分散于胆汁中,其多色性、吸收性不明显,但边缘和贝克线很清楚,折射率大于胆汁折射率;在正交偏光镜下,呈现出特殊的干涉图样,载物台在３６０度转动过程中呈现出四次消光现象,光性符号是单轴正性的;干涉色级是一级灰白,双折射率△ｎ＝０．０１１－０．０１５。     

Physico-chemical properties and evidence for electrophoretic variants of rat transcortin

Isolation of rat plasma transcortin was carried out by affinity chromatography, as previously described for human. The protein was shown to be pure by PAGE and one single N-terminal amino acid was identified (Ser), which suggested that the protein molecule has a single polypeptide chain. This assumption is supported by SDS-PAGE. The amino acid composition was reported and compared with the one of human transcortin. The purified protein always migrated in PAGE (with or without SDS) as a double band; the faster component being more intense than the slower one. Whether transcortin was free or bound to corticosterone, the same aspect was observed. Molecular weight of these two variants were determined by SDS-PAGE as 65,900 and 75,800. Polymers only appeared after irreversible denaturation of the protein, as previously described for human transcortin. Various other physical parameters were determined: a sedimentation coefficient of 3.71 S +/- 0.18 was calculated by ultracentrifugation in sucrose gradient, association constants at 4 degrees C for corticosterone and cortisol (2.7 X 10(9) M-1 and 4.2 X 10(8) M-1, respectively).     

Comparison of chemical properties of purified plasma membranes and secretory vesicle membranes from the bovine adrenal medulla

Summary A highly enriched fraction of plasma membranes from the bovine adrenal medulla has been isolated by differential and sucrose gradient centrifugation. The membranes were found to occur as 0.1–0.5 diameter vesicles and to equilibrate at a density of 1.13–1.14 g/ml. This fraction was characterized by 4-fold elevated levels of adenylate cyclase and 20-fold elevated levels of 5-nucleotidase. Secretory vesicle membranes, isolated by repeated hypotonie and hypertonic shocks of whole vesicles, were found to equilibrate between d = 1.08 and d = 1.12 on a sucrose density step gradient. These membranes were highly enriched in cytochrome b₅₆₂ and dopamine--hydroxylase. Proteins in the two membranes were compared by SDS gel electrophoresis. All protein size classes found in the vesicle membrane fraction were also represented in the plasma membrane fraction, though in different proportions on the basis of staining intensity. The plasma membrane fraction contained prominent bands co-migrating with the - and -bands of tubulin, as well as a component co-migrating with actin. These bands were absent from the vesicle membranes. Fingerprint analysis of stained bands from the membrane fraction demonstrated that the components were indeed tubulin and actin. The plasma membranes contained twice as much sialic acid residues as did the chromaffin granule membranes, but had only half the cholesterol content on a weight basis. The cholesterolphospholipid ratio in the plasma membranes was 0.63, while in the secretory vesicle membranes it was 1.04. These results show that plasma membranes and secretory vesicle membranes are functionally and structurally different.Supported, in part, by a stipend to O.Z. from The Grant Foundation, New York     

Properties of polyphenol oxidase from tubers of the yam Dioscorea bulbifera

The subunit MW of Dioscorea bulbifera polyphenol oxidase (MW 115 000 ± 2000) determined by SDS-PAGE is ca. 31 000 indicating that the enzyme is an oligomeric protein with four subunits. K_i values of various inhibitors and their modes of inhibition have been determined with catechol and pyrogallol as substrates. p-Nitrophenol, p-cresol, quinoline and resorcinol are competitive inhibitors of catechol binding while only orcinol and p-nitrophenol behave in the same way towards pyrogallol as substrate. From the effect of pH on V_max, groups with pK values ca. 4.7 and 6.8 have been identified to be involved in catalytic activity. The Arrhenius activation energy (E_a) at pH 4.0 is 8.9 kcal/mol between 40–65°. At pH 7.0, the value is 22.1 kcal/mol between 40 and 60°. The enthalpies (ΔH) at pH 4.0 and pH 7.0 are 2.3 kcal/mol and 32.4 kcal/mol respectively. The results are discussed considering the conformational changes of the enzyme during substrate binding.     

A study of the surface-active properties of the Mg2+-activated ATPase from cytoplasmic membranes of Streptococcus faecalis

The surface activity and enzymic properties of the factor F₁, the catalytic moiety of Streptococcus faecalis H⁺-ATPase, has been studied at the air-water and phospholipid-water interfaces. F₁ does not interact with the monolayer phospholipids, hence its adsorption on a biological membrane must be due mainly to its recognition of proteins of the hydrophobic complex. The dimensions of the F₁ molecule at the air-water interface have been estimated. In the presence of Mg²⁺, base area is $\text{S = 1.8 · 10}{}^4\text{A}\text{?}{}^2$, height $\text{h = 27}\text{A}\text{?}$. Bearing in mind the size of a globular subunit, it follows from the measurements that the major F₁ subunits should all lie in the same plane. The ATPase activity of F₁ at the interface is inversely proportional to the monolayer density. With low density monolayer, the specific ATPase activity is higher at the interface than in the bulk of the solution.Adsorption of F₁ at the interface shifts the isoelectric point of the protein, apparently due to changes in its conformation. The findings are discussed relative to the proton-active transport mechanism.     

The influence of pH on the EPR and redox properties of cytochrome c oxidase in detergent solution and in phospholipid vesicles

The EPR signals of oxidized and partially reduced cytochrome oxidase have been studied at pH 6.4, 7.4, and 8.4. Isolated cytochrome oxidase in both non-ionic detergent solution and in phospholipid vesicles has been used in reductive titrations with ferrocytochrome c.The g values of the low- and high-field parts of the low-spin heme signal in oxidized cytochrome oxidase are shown to be pH dependent. In reductive titrations, low-spin heme signals at g 2.6 as well as rhombic and nearly axial high-spin heme signals are found at pH 8.4, while the only heme signals appearing at pH 6.4 are two nearly axial g 6 signals. This pH dependence is shifted in the vesicles.The g 2.6 signals formed in titrations with ferrocytochrome c at pH 8.4 correspond maximally to 0.25–0.35 heme per functional unit (aa₃) of cytochrome oxidase in detergent solution and to 0.22 heme in vesicle oxidase. The total amount of high-spin heme signals at g 6 found in partially reduced enzyme is 0.45–0.6 at pH 6.4 and 0.1–0.2 at pH 8.4. In titrations of cytochrome oxidase in detergent solution the g 1.45 and g 2 signals disappear with fewer equivalents of ferrocytochrome c added at pH 8.4 compared to pH 6.4.The results indicate that the environment of the hemes varies with the pH. One change is interpreted as cytochrome a₃ being converted from a high-spin to a low-spin form when the pH is increased. Possibly this transition is related to a change of a liganded H₂O to OH^? with a concomitant decrease of the redox potential. Oxidase in phosphatidylcholine vesicles is found to behave as if it experiences a pH, one unit lower than that of the medium.     

The mechanism of deuterium oxide-induced protein degradation in Lemna minor

Transfer of Lemna minor fronds to culture medium containing 50% (v/v) deuterium oxide induces a large increase in the rate of protein breakdown, which is not due to an increase in the activity of acidic or neutral proteolytic enzymes or peptidases. Biochemical and ultrastructural evidence indicates that deuterium oxide affects the properties of certain membranes, particularly the tonoplast, and allows vacuolar proteolytic enzymes to pass into the cytoplasm and cause the increased protein breakdown.Abbreviations BAPA benzylarginine-p-nitroanilide - LPA leucine-p-nitroanilide - TCA trichloroacetic acid     

Passive cable properties of hippocampal CA3 pyramidal neurons

The passive electrical cable properties of CA3 pyramidal neurons from guinea pig hippocampal slices were investigated by applying current steps and recording the voltage transients from 25 CA3 neurons, using a single intracellular microelectrode and a 3-kHz time-share system. Two independent methods were used for estimating the equivalent electrotonic length of the dendrites, L, and the dendritic to somatic conductance ratio, . The first method is similar to that used by Gorman and Mirolli (1972) and gave an average L of 0.96; the average was 2.44. The second method is derived here for the first time and assumes a finite-length cable with lumped soma. It is an exact solution for L and , using the slopes and intercepts of the first two peeled exponentials. The average L was 0.94; the average was 1.51. The results, using both methods, are in close agreement. The average membrane time constant for all 25 CA3 neurons was 23.6 ms, suggesting a large (23,600 cm²) average membrane resistivity. It is concluded that CA3 neurons are electronically short.This work was supported by Grants NS 11535 and NS 15772 from the National Institute of Neurological and Communicative Disorders and Stroke, National Institutes of Health, U.S. Public Health Service.     

Purification and properties of O-acetyl-L-serine sulphydrylase from wheat leaves

O-Acetyl-L-serine sulphydrylase (OASS), the enzyme which produces L-cysteine from O-acetyl-L-serine (OAS) and sulphide, is     

An unusual allantoinase from Dolichos biflorus

An unusual allantoinase from Dolichos biflorus has been purified 62-fold. The purified enzyme has an unusual pH activity profile with a shoulder at pH 4 and a peak at pH 7.5. This is due to a single enzyme which does not need metal ions for activation. In the fully reduced state the enzyme exhibits a single sharp peak at 7.5; when it is not in the sulfhydryl form (in the fully oxidized SS form?) the enzyme shows a single pH optimum at pH 4. K_m values for (±)-allantoin were 5.5 mM at pH 4 and 1.43 mM at pH 7.5. Allantoinase activity has been demonstrated in the resting seed, and increased linearly with time during the first 5 days of seedling growth.