大壁虎的染色体及减数分裂联会复合体的研究

大壁虎(Gekko gecko)的染色体数目为2n=38,核型由2对中着丝粒(Nos.1.4.)、3对亚中着丝粒(Nos.2.3.5)及14对端着丝粒和亚端着丝粒(Nos.6—19)染色体组成。一对核仁组织者(NOR_s),位于第7对端着丝粒染色体的末端。同时,本文还对大壁虎的减数分裂以及联会复合体(S.C)的结构和组型,进行了详细的观察和分析。     

In vitro effects of cycloheximide and luteinizing hormone on the estradiol-to-progesterone shift in follicular steroidogenesis

The objectives of this study were to establish a completely in vitro system that would simulate the in vivo effects of cycloheximide (cyclo) on preovulatory serum levels of estradiol (E2) (prolonged) and progesterone (P4) (reduced). Graafian follicles were removed from proestrous hamsters at 0900 h and incubated for a basal hour (Hour 1) with various doses of cyclo before the medium was replaced; in Hour 2, 100 ng luteinizing hormone (LH) was added with cyclo added every hour for 5 or 6 h. The endpoints were steroid levels/follicle/h per ml medium of P4, 17 alpha-hydroxyprogesterone (170HP), androstenedione (A), and E2. The goal was best accomplished with hourly addition of 400 ng cyclo, which reduced follicular protein synthesis by 76%. Cyclo suppressed P4 and 170HP and prolonged the accumulation of A and E2, in Hour 5 and Hour 6, correlated with sustained thecal C-17,20-lyase/17 alpha-hydroxylase as determined by enzyme assays. Cyclo therefore prevented the early demise of the enzyme complex after LH stimulation and hence prolonged the ability of the theca to provide androgens for conversion to E2 by the granulosa cells. Our earlier work established that one of the major effects of LH is to recruit the granulosa compartment as a source of C-21 steroids, and cyclo interferes with the availability of cholesterol to mitochondrial side-chain cleavage (Greenwald and Limback, 1984). Thus, cyclo affects follicular steroidogenesis through different mechanisms in theca and granulosa.     

Urea hydrolysis by immobilized urease in a fixed-bed reactor: analysis and kinetic parameter estimation

Urea hydrolysis by urease immobilized onto ion exchange resins in a fixed-bed reactor has been studied. A modified Michaelis-Menten rate expression is used to describe the pH-dependent, substrate- and product-inhibited kinetics. Ionic equilibria of product and buffer species are included to account for pH changes generated by reaction. An isothermal, heterogeneous plug-flow reactor model has been developed. An effectiveness factor is used to describe the reaction-diffusion process within the particle phase. The procedure for covalent immobilization of urease onto macroporous cation exchangers is described. Urea conversion data are used to estimate kinetic parameters by a simplex optimization method. The best-fitted parameters are then used to predict the outlet conversions and pH values for systems with various inlet pH values, inlet urea and ammonia concentrations, buffers, particle sizes, and spacetimes. Very good agreement is obtained between experimental data and model predictions. This immobilized urease system exhibits quite different kinetic behavior from soluble urease because the pH near the enzyme active sites is different from that of the pore fluid. This effect results in a shift of the optimal pH value of the V(max) (pH) curve from 6.6 (soluble urease) to ca. 7.6 in dialysate solution, and ca. pH 8.0 in 20mM phosphate buffer. The reactor model is especially useful for estimating intrinsic kinetic parameters of immobilized enzymes and for designing urea removal columns.     

Growth and death in overagitated microcarrier cell cultures

The effects of hydrodynamic forces on cell growth are investigated for animal cells growing on microcarriers. A reduction in net growth was observed with high levels of agitation. DNA measurements indicated that the reduction in net growth was due entirely to cell death, from hydrodynamic forces. No inhibition or enhancement of cell replication appeared to occur with high levels of agitation.     

Ca2+ channels in chick neural retina cells characterized by 1,4-dihydropyridine antagonists and activators

The voltage-sensitive calcium channel in cultured chick neural retina cells was characterized by the actions of the enantiomers of Bay K 8644 and 202-791 and other 1,4-dihydropyridines. These cells showed time- and voltage-dependent Ca2+ uptake that was stimulated by K+ depolarization and blocked by the inorganic calcium channel blockers Cd2+ and Co2+. A small fraction only (15% maximum) of the uptake was inactivated by predepolarization of the cells with 80 mM K+. Ca2+ uptake was sensitive to the 1,4-dihydropyridine calcium channel antagonists and activators. (S)-Bay K 8644 and (S)-202-791 stimulated the Ca2+ uptake, and (R)-Bay K 8644 and (R)-202-791 as well as nitrendipine and PN 200-110 inhibited Ca2+ uptake stimulated by K+ depolarization or channel activators. The K+ depolarization-stimulated uptake was inhibited by 90%, but the activator-stimulated uptake was completely blocked by the 1,4-dihydropyridine antagonists. The potencies of these agents as inhibitors of Ca2+ uptake were significantly lower than the binding affinities in membrane preparations from the same cells or their binding and pharmacologic affinities in vascular smooth muscle. K+ depolarization or (S)-Bay K 8644 induced 45Ca2+ uptake was not observed in a glial cell culture. [3H]Nitrendipine and [3H]PN 200-110 bound to membrane preparations of the cells consistent with the presence of a single type of high affinity binding site.(ABSTRACT TRUNCATED AT 250 WORDS)     

Stimulation of progesterone and prostaglandin E2 production by lipoxygenase metabolites of arachidonic acid

The role of several lipoxygenase metabolites of arachidonic acid in the action of luteinizing hormone-releasing hormone (LHRH) on ovarian hormone production was investigated. Like LHRH, treatment of rat granulosa cells with 5-HETE, 5-HPETE, 12-HETE, 15-HETE or 15-HPETE stimulated progesterone (P) and prostaglandin E2 (PGE2) production. 12-HEPE was most potent and stimulated P and PGE2 equally well. By contrast, 5-HETE stimulated P better than PGE2, while 15-HETE was a potent stimulator of PGE2 but not of P. Stimulation of P and PGE2 by LHRH or 12-O-tetradecanoylphorbol 13-acetate (TPA) was further augmented by several HETEs and HPETEs. Like protein kinase C, arachidonic acid metabolites appear to mediate the multiple actions of LHRH in the ovary.     

Molecular genetics of phenylketonuria in Orientals: linkage disequilibrium between a termination mutation and haplotype 4 of the phenylalanine hydroxylase gene.

Phenylketonuria (PKU) is a common metabolic disorder among Chinese, with a prevalence of about 1 in 16,500 births. This frequency is very similar to that among Caucasians. Individual exons of the phenylalanine hydroxylase (PAH) gene with flanking introns were amplified by polymerase chain reaction and cloned into M13 for sequence analysis. An Arg111-to-Ter111 mutation has been identified in exon 3 of the PAH gene in a Chinese PKU patient. The mutation is in linkage disequilibrium with the mutant haplotype 4 alleles which are the most prevalent haplotype among the Orientals. The mutation accounts for about 10% of the Chinese PKU alleles and is absent from the Caucasians, demonstrating that independent mutational events have occurred in the PAH locus after racial divergence.     

Analysis of a glucose-containing tetrasaccharide by high-performance liquid affinity chromatography

In the present work we have explored conditions for using a pulsed amperometric detector for on-line analysis of oligosaccharides eluted from a high-performance liquid affinity chromatography column. A monoclonal antibody that specifically binds a glucose-containing oligosaccharide is coupled to a SelectiSphere-10-activated tresyl column. The system is eluted isocratically and easily detects 10 ng of the oligosaccharide with a linear response up to 250 ng. Analysis of both serum and urine samples from normal individuals and patients with acute pancreatitis gives a single retarded peak with a retention time identical to that of authentic (Glc)4. Retarded material pooled from several analyses of urine was positively identified as (Glc)4 by GC-MS analysis. As this method requires little cleanup and no chemical derivitization of the sample and is performed rapidly (less than 20 min) at sensitivities of at least 10 micrograms/liter in biological fluids, it represents a substantial improvement over previous GC-MS, radioimmunoassay, and enzyme-linked immunoadsorbent assay methods used to determine (Glc)4.