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Biomedical subjects

Y Z Ma

Publications and source records attributed to Y Z Ma.

At least 19 recordsLinked to original sources
PubMed2001

Temporal patterns of circulating leptin levels in lean and obese adolescents: relationships to insulin, growth hormone, and free fatty acids rhythmicity.

Alterations in nutritional status, such as obesity, markedly influence insulin, leptin, GH secretion, and free fatty acid (FFA) levels. We measured every hour for 24 h circulating leptin, insulin, GH, and FFA levels in lean and obese adolescents to determine: 1) the impact of adolescent obesity on the diurnal changes in leptin concentrations; and 2) the temporal relationships between the diurnal patterns of circulating leptin levels and insulin, GH, and FFA levels. During puberty, we found that the 24-h profile of circulating plasma leptin levels follows a bimodal pattern with minimal concentrations occurring early in the afternoon and a nocturnal elevation starting after midnight and culminating early morning. The time course of the diurnal variation in leptin levels in the obese adolescents was not different from that in lean controls. Of note, however, in obese girls leptin 24-h excursion and leptin night to day ratio were lower than those found in lean girls. In obese adolescents, mean GH levels varied significantly less during the day and night than lean controls. During the day, there were distinct preprandial increases and postprandial decreases in FFA levels, whereas after midnight FFA levels rose in both lean and obese adolescents. A significant positive correlation was found between mean plasma insulin levels between 0800 h and 2000 h and peak in leptin in lean and obese girls and boys (r = 0.63, P: < 0.001). Peak leptin was inversely correlated with the area under the nocturnal GH levels in all groups (r = -0.31, P: < 0.0003), whereas it was positively correlated with the nocturnal peak in FFA levels (r = 0.45, P: < 0.004). In summary, we report in obese adolescent girls a blunted relative diurnal excursion in leptin levels. This abnormal rhythmicity may, in part, explain their leptin resistance state. The nocturnal rise in leptin was paralleled by a nocturnal rise in GH and FFA levels. Additional studies are needed to test the potential link between the adipose-derived peptide and GH axis in humans.

Adolescent↗
PubMed2001

[Development of donor cells in chicken-duck chimeric embryos].

Chicken W chromosome-specific DNA fragments were obtained after transformation, extraction, purification and digestion with EcoR I of pUGD1201. The W chromosome-specific DNA probe was a 1.2 kb insert, which was labelled by the random-technique using a Digoxigenin Labeling Kit. Chicken PGCs from a line of White Leghorns were microinjected into Maya duck blastoderms at stage X. The embryos at 6,8,9,12,16,18 days of incubation were used to study the development of chicken PGCs in the chimeric embryos. Used chicken W chromosome-specific DNA probes by in situ hybridization, development of donor cells in chicken-duck chimeric embryos were studied. In 54 chimeric embryos, there were different degrees of chimerism in the organs. The chimeric rate of the livers was the highest, which of the gonads was the lowest. It is demonstrated that somatic and germline chimeras can be yielded successfully by transferring stage X chicken blastodermal cells.

Animals↗
PubMed2000

Kinetics of absorbance and anisotropy upon excited state relaxation in the reaction center core complex of a green sulfur bacterium.

Properties of the excited states in reaction center core (RCC) complexes of the green sulfur bacterium Prosthecochloris aestuarii were studied by means of femtosecond time-resolved isotropic and anisotropic absorption difference spectroscopy at 275 K. Selective excitation of the different transitions of the complex resulted in the rapid establishment of a thermal equilibrium. At about 1 ps after excitation, the energy was located at the lowest energy transition, BChl a 835. Time constants varying between 0.26 and 0.46 ps were observed for the energy transfer steps leading to this equilibrium. These transfer steps were also reflected in changes in polarization. Our measurements indicate that downhill energy transfer towards excited BChl a 835 occurs via the energetically higher spectral forms BChl a 809 and BChl a 820. Low values of the anisotropy of about 0.07 were found in the 'two-color' measurements at 820 and 835 nm upon excitation at 800 nm, whereas the 'one-color' kinetics showed much higher anisotropies. Charge separation occurred with a time constant varying between 20 and 30 ps.

Journal Article↗
PubMed2000

Augmentation of alimentary insulin secretion despite similar gastric inhibitory peptide (GIP) responses in juvenile obesity.

Insulin secretion rates are greater after oral glucose than after parenteral administration of an equivalent glucose load. This augmented beta-cell secretory response to an oral glucose load results from the release of mainly two gut hormones: gastric inhibitory polypeptide (GIP) and glucagon-like peptide-1, which potentiate glucose-induced insulin secretion. Because of their insulinotropic action, their abnormal secretion may be involved in the pathogenesis of the hyperinsulinemia of childhood obesity. In this study, we used the hyperglycemic clamp with a small oral glucose load to assess the effect of childhood obesity on GIP response in seven prepubertal lean and 11 prepubertal obese children and in 14 lean adolescents and 10 obese adolescents. Plasma glucose was acutely raised to 11 mM by infusing i.v. glucose and kept at this concentration for 180 min. Each subject ingested oral glucose (30 g) at 120 min, and the glucose infusion was adjusted to maintain the plasma glucose plateau. Basal insulin and C-peptide concentrations and insulin secretion rates (calculated by the deconvolution method) were significantly greater in obese children compared with lean children (p < 0.001). Similarly, during the first 120 min of the clamp, insulin secretion rates were higher in obese than lean children. After oral glucose, plasma insulin, C-peptide, and insulin secretion rates further increased in all four groups. This incretin effect was 2-fold greater in obese versus lean adolescents (p < 0.001). Circulating plasma GIP concentrations were similar at baseline in all four groups and remained unchanged during the first 120 min of the clamp. After oral glucose, plasma GIP concentrations rose sharply in all groups (p < 0.002). Of note, the rise in GIP was similar in both lean and obese children. In conclusion, under conditions of stable hyperglycemia, the ingestion of a small amount of glucose elicited equivalent GIP responses in both lean and obese children. However, despite similar GIP responses, insulin secretion was markedly augmented in obese adolescents. Thus, in juvenile obesity, excessive alimentary beta-cell stimulation may be independent of the increased release of GIP.

Administration, Oral↗
PubMed2000

Effect of carotenoid biosynthesis inhibition on the chlorosome organization in Chlorobium phaeobacteroides strain CL1401.

We have studied the effect of the absence of carotenoids on the organization of bacteriochlorophylls (BChls) in chlorosomes of Chlorobium (Chl.) phaeobacteroides strain CL1401. Carotenoid-depleted chlorosomes were obtained by means of 2-hydroxybiphenyl-supplemented cultures. In the presence of the inhibitor, isorenieratene (Isr) and beta-Isr biosynthesis were inhibited to more than 95%, leading to an accumulation of the colorless precursor phytoene inside the chlorosomes. In addition, there was a 30-40% decrease in the baseplate BChl a content. The absorption spectrum of the carotenoid-depleted chlorosomes showed a 10 nm blue shift in the BChl e Qy absorption peak. Under reducing conditions, a decrease in the BChl a/BChl e fluorescence emission ratio was observed in carotenoid-depleted chlorosomes relative to that in control chlorosomes, caused mainly by the decrease in the BChl a content. The steady-state fluorescence emission anisotropy in the BChl e region dropped from approximately 0.24 for native chlorosomes to approximately 0.14 for carotenoid-depleted ones, indicating reorganization of BChl e. The circular dichroism (CD) signal of the carotenoid-depleted chlorosomes was increased two times in the BChl e Qy region. A simple model based on the structure proposed was used to explain the observed effects. Carotenoids might affect the angle between the direction of the BChl e Qy transition and the axis of the rod. The orientation of BChl a in the baseplate remains unchanged in carotenoid-depleted chlorosomes, although there is a partial loss of BChl a as a consequence of a decrease in the baseplate size. The carotenoids are most likely rather close to the BChls and appear to be important for the aggregate structure in Chl. phaeobacteroides.

Carotenoids↗
PubMed2000

[Molecular cytogenetic characterization of a new wheat line YW443 with resistance to barley yellow dwarf virus].

A new wheat line YW443 with BYDV resistance and good traits was developed from the combination of PP9-1/Shan7859¿Fengkang 8. The wheat line YW443 was identified by BYDV resistance analysis, genomic in situ hybridization (GISH), RFLP and RAPD analysis. The results indicated as follows: (1) YW443 was resistant to GPV and GAV strains of BYDV; (2) YW443 is a homozygous wheat-Thinopyrum intermedium translocation line with a pair of BYDV resistance genes; (3) The 7StL segment of Th. intermedium carring BYDV resistance gene was transferred onto the distal end of the wheat chromosome 7D long arm, the line YW443 was 7DS.7DL-7StL translocation; (4) A RAPD marker OPR19(-900) could detect the DNA of Th. intermedium 7StL in L1 and L1 derivatives including translocation lines YW443, YW642 etc. The markers may be used as a selecting marker for the BYDV resistance breeding program.

In Situ Hybridization↗
PubMed2000

[Identification of the barley chromosome in wheat by GISH and RFLP].

The barley chromosome in wheat was identified by genomic in situ hybridization (GISH) in which biotin labelled total genomic DNA of barley Betzes was used as probe and the unlabelled total DNA of common wheat Chinese Spring (CS) as blocking DNA. A series of wheat materials were tested as follows: two disomic alien substitution and monosomic alien addition lines, 2n = 43; two monosomic alien substitution lines, 2n = 42; seven disomic alien substitution lines, 2n = 42. RFLP probe psr131 on the short arm of the homologous group 2 was used to analyze the barley chromosome in wheat. The result indicated that there was a same band in barley Betzes and substitution line A5. The chromosome 2A of A5 was substituted by the chromosome 2H of barley. These materials will be useful in transferring the valuable genes in the chromosome 2H to wheat.

Chromosomes↗
PubMed1998

[Using the lower leg lateral skin flap to reconstruct oral and maxillofacial soft tissue defects (9 cases report)]

OBJECTIVE:In order to investigate the clinical value of lower leg lateral skin flap for the reconstructin of soft tissue defects at oral-maxillofacial regions. METHODS: 9 cases of different soft tissue defects of oral and maxillofacial regions were under went surgery with leg lateral skin flap transplantion in out patients department. RESULTS: All the 9 flaps were got success of one stage repair. This paper describes in detail the anatomy of the flap,technique of make up the flap, clinical application,advantages and disadvantages. CONCLUSION: The lower leg lateral skin flap is versatile flap,but is not the one for first choice.

Journal Article↗
PubMed1997

Kinetic mechanism of a monomeric kinesin construct.

The kinetic mechanism is analyzed for a monomeric human kinesin construct K332. In the absence of microtubules, the rate constants of the ATPase cycle are very similar to dimeric human kinesin K379 and whole kinesin from bovine brain. The microtubule-activated ATPase is 60 s(-1) at 20 degrees C; Km(Mt) is 5 microM; dissociation constants in the presence of ATP and ADP are 9 microM and 16 microM, respectively. The values of dissociation constants are 5 times larger than for K379. Binding of K332 to microtubules increased the rate of the hydrolysis step from 7 s(-1) to greater than 200 s(-1) and the 2'-(3')-O-(N-methylanthraniloyl) (mant) ADP dissociation step from 0.02 s(-1) to greater than 100 s(-1). At higher ionic strength, more than one ATP is hydrolyzed before dissociation of MtK332 (small processivity). Data are fitted to the kinetic scheme. [equation: see text] Approximate values of rate constants are k1 = 500 s(-1), k2 > or = 200 s(-1), k3k4/(k3 + k4) = 100 s(-1), k(dis) = 80+/-10 s(-1). Two experiments to measure k4 gave 110 s(-1) from the maximum rate of dissociation of mant ADP for reaction of K x ADP with microtubules and 300 s(-1) from extrapolation to zero concentration of rate of binding of mant ADP to MtK. It is proposed that mant ADP dissociation is a two-step process. In the simple scheme, k4 is the effective rate of the two-step release of ADP, k4 = 150 s(-1) to 200 s(-1), and k3 = 150 s(-1) to 200 s(-1) to account for the steady state rate.

Adenosine Diphosphate↗
PubMed1997

Interacting head mechanism of microtubule-kinesin ATPase.

Kinetic and equilibrium properties are compared for a monomeric kinesin construct (K332) and a dimeric construct (K379). MtK379 has a low affinity (5 x 10(4) M(-1)) and a high affinity (5 x 10(6) M(-1)) binding site for mant ADP while MtK332 has a single low affinity site (5 x 10(4) M(-1)). Rate constants of dissociation of mant ADP are <1 s(-1) for the high affinity site and 75-100 s(-1) for the low affinity site for MtK379. For MtK332, the effective rate constant is 200-300 s(-1). It is proposed that the two heads of the dimer are different through the interaction with the microtubule, a strongly bound head with low affinity for 2'-(3')-O-(N-methylanthraniloyl) adenosine 5'-diphosphate (mant ADP), similar to the single strongly bound head of the monomer and a weakly bound or detached head with high affinity for mant ADP. Rate of binding of mant ADP gave an "S"-shaped dependence on concentration for MtK379 and a hyperbolic dependence for MtK332. Binding of K379 x mant ADP dimer to microtubules releases only one mant ADP at a rate of 50 s(-1). The second strongly bound mant ADP is released by binding of nucleotides to the other head. Rates are 100 s(-1) for ATP, 30 s(-1) for AMPPNP or ATPgammaS, and 2 s(-1) for ADP. The rate of binding of mant ATP to MtK379 showed an "S"-shaped concentration dependence and limiting rate at zero concentration is <1 s(-1) while MtK332 gave a hyperbolic dependence and limiting rate of 100 s(-1). The limiting rate is determined by the rate of dissociation of mant ADP in the hydrolysis cycle. The evidence is consistent with an interacting site model in which binding of ATP to one head is required for release of ADP from the other head in the hydrolysis cycle. This model, in which the cycles are maintained partly out of phase, is an extension of the alternating site model of Hackney (Hackney, D. D. (1994) Proc. Nat. Acad. Sci. U.S.A. 91, 6865-6869). It provides a basis for a processive mechanism.

Adenosine Diphosphate↗
PubMed1995

Kinetic mechanism of kinesin motor domain.

The kinetic mechanism of the human kinesin ATPase motor domain K379, expressed in Escherichia coli, was determined by transient and steady-state kinetic studies. The steps in nucleotide binding were measured using the fluorescent substrate analogues, methylanthraniloyl ATP (mant-ATP) and mant-ADP. Both nucleotides gave a two-step fluorescence signal, an increase followed by a decrease, which indicates that two isomerizations are induced by nucleotide binding. The ATPase mechanism is fitted by a six-step reaction: [formula: see text] where, T, D, and P refer to nucleotide triphosphate, nucleotide diphosphate, and inorganic phosphate, respectively; K(T) and K(D) are states in rapid equilibrium with the free nucleotide. A set of kinetic constants for 20 degrees C 50 mM NaCl is K1 = 2 x 10(4) M-1, k2 = 200 s-1, k3 = 9 s-1, k5 = 0.01 s-1, and K6 = 2 x 10(-5) M. Values of K1 and K6 are estimates for mant-ATP and mant-ADP, respectively. ADP dissociation is the rate-limiting step. The rate constant for a decrease in fluorescence for the transitions from the high fluorescence K.T state to the low fluorescence K.D state is equal to k3, the rate constant of the hydrolysis step measured by quench flow experiments. The decrease could occur in step 3 or step 4 if k4 > k3.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Diphosphate↗
PubMed1995

Mechanism of microtubule kinesin ATPase.

A six-step mechanism is derived for the activation of kinesin K379 ATPase by microtubules. The data are fitted by the kinetic scheme [Formula see text] where T, D, and P refer to nucleotide triphosphate, nucleotide diphosphate, and inorganic phosphate, respectively; MtK refers to the complex of a K379 unit with the microtubule binding site. The initial binding and release steps, 1 and 6, are treated as rapid equilibria: k2 = 200 s-1, k3 = 100 s-1, k5 = 35-40 s-1, maximum steady-state rate = 25 s-1 (50 mM NaCl, 20 degrees C). k2 was obtained from the maximum rate of fluorescence enhancement with mant-ATP as substrate, k3 was obtained from the hydrolysis transient phase for ATP or mant-ATP, and k5 was obtained from the rate of decrease in fluorescence of mant-ADP in the reaction [Formula see text]. A large excess of ATP was present with the Mt to block rebinding of mant-ADP. The rate was measured as a function of microtubule concentration and extrapolated to give the maximum rate k5. The same method was used to obtain k5 for ADP by mixing K.ADP with microtubules plus excess mant-ATP. The enhancement of fluorescence for the binding of mant-ATP is followed by a decrease in fluorescence with a rate constant of 35-40 s-1. Since the decrease must occur after hydrolysis, it may be correlated with a step or steps leading to the low fluorescence MtK.D state. In the kinetic scheme, steps 4 and 5 both contribute to determining the maximum turnover rate. At higher ionic strengths or lower protein concentrations, the MtK complex is dissociated by ATP. The maximum rate is 12 +/- 2 s-1 in 50 mM NaCl; consequently, hydrolysis occurs before dissociation. The dissociation constant of MtK in the presence of ADP is twice as large as the dissociation constant in the presence of ATP and four times larger than the KM for microtubule activation. The proposed kinetic scheme, which treats the K379 units of a dimer as independent, provides a satisfactory description of the transient and steady-state properties of the system with the possible exception of results at very low substrate concentrations.

Adenosine Diphosphate↗
PubMed1994

Kinetic mechanism of myofibril ATPase.

The kinetic mechanism of myofibril ATPase was investigated using psoas and mixed back muscle over a range of ionic strengths. Myofibrils were labeled with pyrene iodoacetamide to measure the rate constants for the binding of ATP and formation of the weakly attached state. The velocity of shortening was measured by stopping the contraction at various times by mixing with pH 4.5 buffer. The transient and steady-state rates of ATP hydrolysis were measured by the quench flow method. The results fitted the kinetic scheme [formula: see text] The rate constants (or equilibrium constants for steps 1 and 6) were obtained for the six steps. k5 was calculated from the KM for shortening velocity, K1, and k2. The rate constants were essentially equal for myofibrils and acto-S-1 at low ionic strength. Increasing the ionic strength up to 100 mM in NaCl increased the rate of the hydrolysis step and the size of the phosphate burst and the effective rate of product release became the rate-limiting step. The step calculated from the velocity of shortening, k5, and k2 is 15 nm, based on a model in which step 4 is the force-generating step.

Adenosine Diphosphate↗
PubMed1993

Comparison between catalytic activity and activity changes during denaturation by guanidine hydrochloride of enzymes in crystalline state and in solution.

The catalytic activity and activity changes during denaturation by guanidine hydrochloride of glyceraldehyde-3-phosphate dehydrogenase, lactate dehydrogenase and alpha-chymotrypsin in crystalline state and in solution have been compared. The catalytic activities are lower in crystalline state than in solution. Enzymes in crystalline state are more stable than in solution during denaturation by guanidine hydrochloride. Ammonium sulfate has different effects on catalytic activities of different enzymes and shows protection on all enzymes studied during denaturation by guanidine hydrochloride. The protection is more obvious at high concentrations of guanidine hydrochloride than at low concentrations. It is suggested that the flexibility or mobility of enzyme is required for the catalytic activity and related to the stability of enzymes. Enzymes with less flexibility or mobility are more stable.

Ammonium Sulfate↗
PubMed1991

Comparison of the activity and conformation changes of lactate dehydrogenase H4 during denaturation by guanidinium chloride.

The inactivation and unfolding of lactate dehydrogenase (LDH) during denaturation by guanidinium chloride (GuHCl) under diverse conditions have been compared. Unfolding of the native conformation, as monitored by fluorescence and c.d. measurements, occurs in two stages with increasing GuHCl concentrations, and the inactivation approximately coincides with, but slightly precedes, the first stage of unfolding. The enzyme is inhibited to about 60-70% of its original activity by cross-linking with glutaraldehyde or in the presence of 1 M-(NH4)2SO4, with its conformation stabilized as shown by the requirement for higher GuHCl concentrations to bring about both inactivation and unfolding. Low concentrations of GuHCl (0.2-0.4 M) activate the cross-linked and the (NH4)2SO4-inhibited enzyme back to the level of the native enzyme. For the enzyme stabilized by (NH4)2SO4 or by cross-linking with glutaraldehyde, inactivation occurs at a markedly lower GuHCl concentration than that required to bring about its first stage of unfolding. It is concluded that the active site of LDH is situated in a limited region relatively fragile in conformation as compared with the molecule as a whole. The GuHCl activation of LDH stabilized in (NH4)2SO4 or by cross-linking with glutaraldehyde suggests that this fragility and consequently flexibility of the active site is required for its catalytic activity.

Animals↗
PubMed1989

Actin and Myosin in pea tendrils.

We demonstrate here the presence of actin and myosin in pea (Pisum sativum L.) tendrils. The molecular weight of tendril actin is 43,000, the same as rabbit skeletal muscle actin. The native molecular weight of tendril myosin is about 440,000. Tendril myosin is composed of two heavy chains of molecular weight approximately 165,000 and four (two pairs) light chains of 17,000 and 15,000. At high ionic strength, the ATPase activity of pea tendril myosin is activated by K(+)-EDTA and Ca(2+) and is inhibited by Mg(2+). At low ionic strength, the Mg(2+)-ATPase activity of pea tendril myosin is activated by rabbit skeletal muscle F-actin. Superprecipitation occurred after incubation at room temperature when ATP was added to the crude actomyosin extract. It is suggested that the interaction of actin and myosin may play a role in the coiling movement of pea tendril.

Journal Article↗
PubMed1989

Main stem sink manipulation in wheat : effects on nitrogen allocation to tillers.

The role of main stem (MS) sink size on N use by field-grown soft red winter wheat (Triticum aestivum L. cv Hart) was determined. At Feeke's growth stage 8 (last leaf just visible), 100 micromoles of 99 atom% (15)N-ammonium was injected into the lower MS. At anthesis, MS sink size was adjusted by removal of 0, 33, 66, and 100% of the MS spikelets; tiller spikes were left intact. The MS and tiller average kernel size was unaffected by MS sink manipulations. The MS kernel N concentration increased when MS spikelets were removed. Tiller kernel N concentrations were unaffected except when the entire MS reproductive sink was removed, which caused an increase in tiller kernel N concentration. Net losses of MS vegetative N during grain fill were similar for all treatments except for plants lacking MS spikelets, which mobilized 30% less N from the MS. Labeled N was predominately (>90%) associated with the insoluble reduced N fraction of plant tissues at anthesis. Allocation of labeled N to tillers was not proportional to reduction in MS sink size. These results indicate that the reproductive sink on an individual culm has first priority for vegetative N mobilized during grain fill even when sink demand is reduced substantially.

Journal Article↗