A role for zeta protein kinase C in nerve growth factor-induced differentiation of PC12 cells

Studies were undertaken to compare the signal-induced redistribution of conventional protein kinase C (cPKC) to nonclassical protein kinase C (nPKC) family members in response to phorbol 12-myristate 13-acetate (PMA) or nerve growth factor (NGF) treatment of PC12 cells. cPKC-alpha and -beta and nPKC-delta and -epsilon were predominantly cytoplasmic, whereas PKC-zeta displayed approximately equal distribution between the cytoplasm and membrane fraction. Treatment of PC12 cells with PMA induced rapid translocation of both c- and nPKC isoforms to the membrane fraction, although the kinetics varied between isoforms with epsilon being most sensitive, followed by delta > zeta > alpha. Both PKC-epsilon and delta translocated in the presence of minute concentrations of PMA, whereas cPKC was less sensitive, and PKC-zeta was least sensitive. NGF treatment, on the other hand, induced translocation of cPKCs and delta and epsilon nPKC, albeit with differential magnitude, whereas PKC-zeta was found predominantly in the cytoplasm. Chronic treatment of PC12 cells with PMA (1 microM) caused a rapid disappearance of alpha, beta, delta, and epsilon PKC isoforms, whereas the expression of PKC-zeta was unaltered over 4 days. NGF induced an increase in cytoplasmic PKC-zeta in control, or PMA down-regulated PC12 cells. Moreover, the increase in cytoplasmic PKC-zeta was blocked by pretreatment with sphingosine (2.5 microM). Furthermore, PKC-zeta was activated by NGF in PMA down-regulated PC12 cells, as determined by the extent of epsilon-peptide phosphorylation using a permeabilized cell assay. In addition, the zeta-pseudosubstrate peptide inhibited NGF-induced activation of PKC-zeta.(ABSTRACT TRUNCATED AT 250 WORDS)

Binding of purine nucleotides to two regulatory sites results in synergistic feedback inhibition of glutamine 5-phosphoribosylpyrophosphate amidotransferase

Glutamine 5-phosphoribosylpyrophosphate amidotransferase from Escherichia coli is subject to synergistic feedback regulation by adenine and guanine nucleotides. Inhibition assays and equilibrium binding measurements have established that synergistic inhibition by AMP and GMP results from synergistic binding to two sites/enzyme subunit in the homotetramer. Although each nucleotide can bind to both sites, analyses of the wild type and mutant enzymes indicate that binding of GMP to an A (allosteric) site and AMP to a proximal C (catalytic) site are necessary for synergistic inhibition. K326Q and P410W amino acid replacements result in decreased binding affinity for GMP and AMP and lead to corresponding reductions in feedback inhibition. The K326Q A site mutation results not only in decreased affinity of GMP for the mutant A site but also has an adverse effect on AMP affinity for the C site. Similarly, the P410W C site mutation has a detrimental effect on binding of AMP to the mutant C site and also on affinity of GMP to the A site. The fact that a mutation in one site affects binding of nucleotides to both sites provides further evidence for synergistic binding of nucleotides.

Two genes for de novo purine nucleotide synthesis on human chromosome 4 are closely linked and divergently transcribed

A cDNA encoding human glutamine phosphoribosylpyrophosphate amidotransferase for step one in de novo purine nucleotide synthesis was cloned, sequenced, and expressed in Chinese hamster ovary cells to yield functional enzyme. Enzyme function was dependent upon removal of an 11-amino-acid propeptide. A mutant enzyme having three propeptide amino acid replacements was not processed and was not active. The human genes GPAT, encoding the amidotransferase, and AIRC, encoding a bifunctional enzyme for steps six and seven in the pathway, were cloned and characterized. GPAT and AIRC are closely linked and divergently transcribed from an intergenic region of approximately 625 base pairs. Expression of a luciferase reporter from the GPAT promoter was approximately 3-4-fold higher than from the AIRC promoter. The GPAT gene was mapped to the q12 region of chromosome 4.

[Discovery and clinical investigation of Lyme disease in Beijing area]

The investigation of Lyme disease in Beijing area is reported for the first time. The sera of 1314 local residents were examined by indirect immunofluorescent assay. 11.9% of them were seropositive to Borrelia burgdorferi. The principal vector was Haemapsysalis longicornis. Six strains of B. burgdorferi were isolated from ticks or patients using modified BSK medium. Spirochetes were found in 5 of 30 patients' skin biopsy samples. Penicillin or ceftriaxone was used to treat the patients, and the effective rates were 64% and 88%, respectively.

Traditional Chinese medicine typing of affective disorders and treatment

According to the theory of Traditional Chinese Medicine (TCM), 50 patients with affective disorders were typed into the categories of depressed liver resulting in fire, mild Yang deficiency and mild Yin deficiency and were treated with Xiao Yao San Jia Wei. The results are 26 patients with marked improvement, 17 patients with improvement and 7 patients with no improvement.

Efficiency of searchpatterns

Search theory deals with the efficiency of covering searchpatterns; a classical example is systematic row search with sweep spacing dependent upon window size. Human visual search is a function of contrast and size of the targets and of effective visual lobe size, this latter influenced by clutter and foveal load. Human searchpatterns often are optimal covers. Experimental results presented in this paper demonstrate that this is true for instrumental search with display windows controlled by human subjects and quantified with a formula for efficiency. Visual searchpatterns using free eye movements often develop complex irregular sequential searchpatterns.

Angiotensin-converting enzyme and myocardial fibrosis in the rat receiving angiotensin II or aldosterone

Angiotensin-converting enzyme (ACE) is present in tissues composed largely of fibrillar collagen such as heart valves, the adventitia of great vessels and intramyocardial coronary arteries, and the scar that follows myocardial infarction. We tested the hypothesis that such tissue ACE is related to fibrous tissue formation and that its appearance is independent of circulating renin and angiotensin peptides. For this purpose we selected experimental models that simulate primary and secondary hyperaldosteronism, each of which are associated with the appearance of myocardial fibrosis. ACE in the excised heart and aorta was localized by in vitro autoradiography with [125I]351A, while fibrosis was identified by light microscopy in sections stained with collagen specific picrosirius red. Tissue was obtained at 2, 4, and 6 weeks from various experimental groups: unoperated, untreated, age- and sex-matched controls; age- and sex-matched uninephrectomized control rats on a high sodium diet; and rats that had received either aldosterone (ALDO) or angiotensin II (AII). Compared with controls, we found ACE binding (1) unchanged after 2 weeks of ALDO, but increased in the adventitia of intramural coronary arteries after 4 weeks, in keeping with the perivascular fibrosis that appeared in each ventricle; (2) markedly increased after 6 weeks of ALDO, where it not only involved coronary vessels but also microscopic scars that appeared in atria and ventricles; (3) increased in the coronary adventitia and sites of scarring, each of which were present 2 weeks after AII; and (4) markedly increased after 4 and 6 weeks of AII as fibrosis became more extensive.(ABSTRACT TRUNCATED AT 250 WORDS)

Expression and characterization of rat kallikrein-binding protein in Escherichia coli

Rat kallikrein-binding protein is a novel serine-proteinase inhibitor that forms a covalent complex with tissue kallikrein. We have purified rat kallikrein-binding protein and cloned the cDNA and the gene encoding rat kallikrein-binding protein [Chao, Chai, Chen, Xiong, Chao, Woodley-Miller, Wang, Lu and Chao (1990) J. Biol. Chem. 265, 16394-16401; Chai, Ma, Murray, Chao and Chao (1991) J. Biol. Chem. 266, 16029-16036]. In the present study, we have expressed rat kallikrein-binding protein in Escherichia coli with a T7-polymerase/promoter expression system. A high level of expression was detected by an e.l.i.s.a. with an average of 24.2 mg of recombinant rat kallikrein-binding protein per 1 of culture. The recombinant protein appeared as a major protein in a crude extract of Escherichia coli on SDS/PAGE. It showed a molecular mass of 43 kDa and was recognized by polyclonal antibody to the native rat kallikrein-binding protein in Western-blot analysis. The recombinant rat kallikrein-binding protein has been purified to apparent homogeneity by DEAE-Sepharose CL-6B, hydroxyapatite Bio-Gel HPHT and Mono P 5/5 column chromatography. The purified recombinant rat kallikrein-binding protein showed immunological identity with the native rat kallikrein-binding protein purified from rat serum, in a specific e.l.i.s.a. To confirm the fidelity of the expression, the N-terminal ten amino acids of the recombinant rat kallikrein-binding protein were sequenced and were shown to match perfectly with those of the native rat kallikrein-binding protein. The purified recombinant rat kallikrein-binding protein formed SDS- and heat-stable complexes with rat tissue kallikrein (rK1) and T-kininogenase (rK10) in vitro, but not with other enzymes in the rat kallikrein gene family, such as tonin (rK2) and S3 protein (rK9), which indicates enzyme-specific binding. The properties of the recombinant rat kallikrein-binding protein including its size, charge, complex formation with target enzymes and immunological characteristics were compared with those of the native protein. This expression system provides a simple way to obtain a large amount of the biologically active recombinant protein, to study structure-function relationships of the rat kallikrein-binding protein and its interaction with its target enzymes.

Identification of sites for feedback regulation of glutamine 5-phosphoribosylpyrophosphate amidotransferase by nucleotides and relationship to residues important for catalysis

Glutamine phosphoribosylpyrophosphate amidotransferase, the key regulatory enzyme for de novo purine nucleotide synthesis, is subject to feedback regulation by adenine and guanine nucleotides. Affinity labeling with 5'-p-fluorosulfonylbenzoyladenosine (FSBA) and 8-azidoadenosine 5'-monophosphate (N3-AMP) was used to identify purine nucleotide sites for feedback control of the Escherichia coli amidotransferase. FSBA inactivated the amidotransferase with saturation kinetics. Specificity for inactivation was shown by the covalent attachment of 2.0-2.4 eq of [3H] sulfobenzoyladenosine (SBA) per subunit and protection by GMP and AMP against inactivation and incorporation of [3H]SBA. Six chymotryptic peptides modified with [3H]SBA were isolated and identified by differential labeling followed by high performance liquid chromatography and radioactivity. Mass spectrometry and Edman degradation analysis were used to identify 5 residues that were covalently modified by [3H]SBA: Tyr74, Tyr258, Lys326, Tyr329, and Tyr465. Tyr258 was also modified by N3-AMP. Mutant enzymes K326Q and Y329A had activity similar to that of the wild type enzyme. However, both mutants exhibited decreased sensitivity to inhibition by GMP and decreased binding of GMP but were inhibited by AMP. Mutant enzymes Y74A and Y258F were normally feedback-inhibited but were defective in glutamine amide transfer and synthase functions, respectively. Therefore Tyr74 and Tyr258 are important for activity and modification by FSBA and N3-AMP accounts for enzyme inactivation. These results localize residues important for catalysis in close proximity to a site for nucleotide binding. Two additional mutant enzymes, G331I and N351A, were constructed which were refractory to inhibition by GMP with little change in inhibition by AMP. A replacement of Tyr465 indicates that this residue is not essential for catalysis or feedback inhibition. Overall, these results are interpreted in terms of a two-nucleotide site model with Lys326, Tyr329, Gly331, and Asn351 defining a site required for inhibition by GMP. A second nucleotide site not affinity labeled by analogs is very close to or overlaps with the catalytic site.

A life-sized physical model of the human cochlea with optical holographic readout

A life-sized physical model of the human cochlea is demonstrated. The model consists of two fluid-filled chambers separated by a polymer membrane and connected through a small hole that serves the same functional purpose as the helicotrema. The dimensions of the two chambers were made identical to those of scala vestibuli and scala tympani in the real cochlea. The membrane's width and length are the same as the values measured for the biological basilar membranes, and its thickness is chosen to give it appropriate rigidity. A piezoelectric transducer drives the system via an elastic window (acting as the oval window) on one side of the scala vestibuli. The resulting vibration pattern on the basilar membrane is investigated with an optical novelty filter, with detection sensitivity of 0.3 A at 2 kHz with a 1-Hz bandwidth. The overall response of this model is found to be a good extrapolation of Bekesy's low-frequency data. However, the tuning curves of this model are not as sharp as those found by Rhode, Johnstone, and others from the in vivo measurements. Possible implications of these results are discussed.

[The C/D ratio in normal newborns]

The optic disc and the C/D ratio were examined in 122 newborns to find that the features of the C/D ratio were positive skewness distribution with leptokurtosis, a wide variability, lesser values of the mean, the median and the 95% upper limit, and non-correlation with the length of pregnancy and the height and weight of the baby at birth. The authors suggested that C/D > 0.3 or a binocular difference of > 0.2 could be regarded as one of the criteria of newborn glaucoma. It was also found that more greyish glial tissue was on the optic disc. The scope of the physiological optic cup was determined by the naked status of the central retinal vessels in the pale area.

Coronary microvascular fluid flux and permeability: influence of angiotensin II, aldosterone, and acute arterial hypertension

Vascular permeability of the coronary and mesenteric circulation is increased in association with the arterial hypertension that accompanies either endogenous activation of the renin-angiotensin-aldosterone system (RAAS) or exogenous administration of angiotensin II (AII). Whether this occurs as a result of increased intravascular pressure or of elevations in plasma concentrations of AII or aldosterone (ALDO) (or both) is unclear. This acute study of filtration-independent coronary fluid exchange and macromolecular permeability was undertaken to address these issues in open-chest, anesthetized dogs. The influence of arterial hypertension, with or without associated elevations in plasma AII or ALDO (or both), on coronary permeability was examined by monitoring the response in cardiac lymph flow, protein concentration, and capillary and intramural coronary artery structure. Experimental groups received a 90-minute intravenous infusion of either AII (n = 8), methoxamine (MX; n = 7), or ALDO plus MX (n = 5) in equipotent doses that raised arterial pressure to comparable levels. When we compared these animals with normotensive, instrumented controls (n = 5), we found that (1) lymph flow was a function of arterial and microvascular pressures in each group; (2) increased protein permeability, myocardial edema, extravasated red cells, and infused colloidal carbon were found in both ventricles with AII, together with endothelial discontinuities and enhanced abluminal capillary endothelial vesicle formation, when plasma ALDO had risen significantly in response to AII; and (3) macromolecular permeability was no different from that in controls after MX or ALDO plus MX. Based on this short-term study of acute arterial hypertension, we would conclude that acute elevations in microvascular pressure increase fluid flux, whereas increased circulating effector hormones of the RAAS, not plasma ALDO or hypertension alone, alter coronary microvascular structure and permeability to macromolecules Responsible mechanisms remain to be defined.

Photorefractive delay line for the visualization and processing of time-dependent signals

We present an optical time-delay line based on photorefractive beam coupling in a rotating crystal. The delay line can be tapped continuously or at selected positions.We demonstrate a 64-channel device with a BaTiO(3) crystal rotating at 1.5 rpm, which gives approximately a 167-Hz bandwidth and 0.5 s of time delay for each channel.

Myocardial fibrosis: role of angiotensin II and aldosterone

In this report we review the replacement (i.e., scarring) and reactive (i.e., perivascular and interstitial fibrosis) fibrous tissue responses found in the myocardium in response to effector hormones of the renin-angiotensin-aldosterone system. Experimental data are presented to indicate: a) endogenous or exogenous elevations in plasma angiotensin II are associated with acute cardiac myocyte necrosis and subsequent microscopic scarring; b) chronic elevations in plasma aldosterone (ALDO), relative to Na+ intake, are associated with a perivascular and interstitial fibrosis of the coronary and systemic circulations and are also seen in response to chronic administration of the mineralocorticoid hormone deoxycorticosterone (DOC); and c) chronic mineralocorticoid excess, due to ALDO or DOC, is associated with enhanced urinary K+ excretion, cardiac myocyte necrosis and scarring. Pharmacologic agents which interfere with these effector hormones (e.g., ACE inhibition and ALDO receptor antagonism) protect the myocardium against this pathologic structural remodeling created by the reactive and replacement (reparative) fibrosis. Evidence is also presented to indicate that chronic ACE inhibition is associated with a regression in reactive myocardial fibrosis. Based on these experimental findings we would suggest that clinical trials are indicated to address the prevention and regression of myocardial fibrosis--an important determinant of pathologic structural remodeling and abnormal myocardial stiffness.

A weighting method for predicting protein structural class from amino acid composition

A protein is generally classified into one of the following four structural classes: all alpha, all beta, alpha+beta and alpha/beta. In this paper, based on the weighting to the 20 constituent amino acids, a new method is proposed for predicting the structural class of a protein according to its amino acid composition. The 20 weighting parameters, which reflect the different properties of the 20 constituent amino acids, have been obtained from a training set of proteins through the linear-programming approach. The rate of correct prediction for a training set of proteins by means of the new method was 100%, whereas the highest rate of previous methods was 82.8%. Furthermore, the results showed that the more numerous training proteins, the more effective the new method.

[Glaucomatous hemodynamic changes in central retinal artery and ocular artery]

The hemodynamics of ocular artery (OA) and central retinal artery (CRA) in 100 eyes of 50 normal subjects and 61 eyes of 39 patients with glaucoma were studied with colour doppler image technique. The results showed the hemodynamic characteristics about normal and glaucomatous eyes and that the ischemic change of CRA was one of the high risk factors in glaucomatous visual functional damages. We propose a new classification of glaucomatous hemodynamics and the clinical application of hemodynamic parameters in glaucoma diagnosis. We also, for the first time, make use of hydrodynamic pressure to calculate the retinal perfusion pressure, which explain the phenomena of intraocular pressure increasing with blood flow decreasing and the effect of hyperviscosity as well as cardiovascular disease on glaucoma. A new approach to the research of glaucoma is presented.

[Comparison of constituents in Pueraria thomsonii Benth before and after processing]

Determinations of aqueous extract, alcoholic extract, flavonoids and puerarin as well as ten inorganic elements in Pueraria thomsonii have been made before and after processing. The results showed that the above mentioned ingredients all varied in amount.

Avian glutamine phosphoribosylpyrophosphate amidotransferase propeptide processing and activity are dependent upon essential cysteine residues

Avian glutamine phosphoribosylpyrophosphate amidotransferase contains an NH2-terminal propetide-like sequence. NH2-terminal sequence analysis of immunoaffinity purified enzyme from chicken liver indicates that the propeptide is processed and the mature enzyme starts with Cys. Propeptide processing was investigated by site-directed mutagenesis using a system for expression in HeLa cells. Glutamine-dependent activity and processing were abolished by replacement of the conserved cysteine at position 1, whereas NH3-dependent activity was retained. Cys1 is thus inferred to have a role in glutamine-dependent activity and in propeptide processing. Inactive, insoluble enzymes in which the propeptide was not processed were obtained as a result of replacements of cysteines 415 and 488. Cysteine residues at positions 415 and 488 are inferred to be ligands to an Fe-S cluster on the basis of sequence similarity to the enzyme from Bacillus subtilis. Mutation of Cys269 and Cys295 led to loss of enzyme activity and propeptide processing, although solubility was unchanged. The results suggest that incorporation of an Fe-S cluster is needed for native structure, resultant propeptide processing, and glutamine-dependent activity.

Fiber-optic acoustic Fourier transducer for audio sound processing

We demonstrate a fiber-optic acoustic transducer operating in the audio-frequency regime. The device is made of an array of 120 multimode optical fibers and a photorefractive novelty filter. Each fiber in the array acts as a cantilevered mechanical resonator. The resonant frequencies of the fibers logarithmically sample the acoustic spectrum from approximately 100 Hz to 5 kHz. Laser light is injected into all fibers simultaneously and is reflected from the end of each fiber. An optical novelty filter extracts the acoustic information from the reflected light. The output of the novelty filter is essentially a Fourier transform of the acoustic signal. The background intensity in the transducer output corresponds to a driving amplitude of approximately 50 A. We describe holographic storage of complex sound patterns that use a LiNbO(3) crystal and an acoustic transducer.

Breast volume measurement in 125 young Chinese women

The authors carried out research on breast volume and body surface anatomy of 125 unmarried young women. As a result, an average breast volume for young Chinese women was obtained (325.36 +/- 12.66 ml), and a table together with several linear equations for calculating breast volume were derived. These will provide plastic surgeons with useful tools for designing mammaplasty procedures.

[The study on ultrastructure of gap junction of rat atrial myocytes in primary culture]

We have studied the ultrastructure of gap junction of rat atrial myocytes of primary culture in situ embedded by ultramicrotomy. We observed a kind of gap junction-associated vesicles (GJAV), a kind of cluster of particles which are surrounded by plasma membrane, and a concatenate GJAV complexes (CGJAVC) in some big clusters. We found that both of GJAV and CGJAVC are very near the plasma membrane at the intercellular space, and at the same time they are usually adjacent the assembled GJ. So we infered that they are the pre-body or midproduct of the assembled GJ probably. This article analysed these observes and probed into the process about how to assemble the gap junction.

A clinical and laboratory study of ciclopirox olamine (8% Batrafen) in the treatment of onychomycosis

Ciclopirox olamine, a new synthetic substituted pyridone derivative, is an antimycotic agent with activity against a broad spectrum of pathogenic and nonpathogenic fungi. The clinical efficacy and safety of 8% ciclopirox olamine nail liquor were evaluated in 100 cases with finger (or great toe) onychomycosis. After 16 weeks and 24 weeks of treatment for finger and great toe onychomycosis, respectively, the overall therapeutic results were excellent in 36 cases, good in 17, fair in 24, and poor in 23. The period of treatment was extended in 31 cases; among them, 10 cases showed further improvement. As for in vitro inhibitory activity, the MIC of ciclopirox olamine against T. rubrum and C. albicans was 1 to 4 mg/L and 1 to 16 mg/L, respectively. This study indicates that 8% ciclopirox olamine nail liquor, with its satisfactory efficacy and lack of side effects, is a good remedy for onychomycosis.

[Screening studies on anti-inflammatory function of traditional Chinese herb Gardenia jasminoides Ellis and its possibility in treating soft tissue injuries in animals]

This paper reports the study of six fractions and one chemical constituent isolated from the traditional Chinese herb Gardenia jasminoides. The results showed that two fractions (G5.G6,), alcohol extract (G1) and genipoiside(A) had obvious anti-inflammatory effects and were comparatively effective in treating soft tissue injuries in animals.

Hair chromium levels in patients with vascular diseases

The chromium levels in the hair of patients with hyperlipemia and coronary heart disease were found to be similar to those of healthy controls (p greater than 0.2). In patients with cerebral hemorrhage and cerebral thrombosis, significantly higher hair chromium values were observed than in healthy subjects (p less than 0.001). The possible significance of these findings is discussed.

Clinical experience and surgical anatomy of 32 free anterolateral thigh flap transplantations

The anterolateral thigh flap, first described by Song, is one of the septocutaneous flaps in the thigh. Since November 1985 we have transferred 32 anterolateral thigh flaps successfully without any loss. Six of these flaps were performed in Australia. The vascular pedicles are divided into three types: fasciocutaneous perforator (37.5%-12/32), vertical musculocutaneous perforator (56.2%-18/32) and horizontal musculocutaneous perforator (6.6%-2/32). This paper presents the surgical anatomy of the flap and clinical experience.

[1-stage reconstruction of microtia associated with hemifacial soft tissue aplasia]

Four cases of microtia association with hemifacial aplasia were repaired by one-stage reconstruction. The operations included external ear reconstruction and correction of facial deformity with free vascularized dermis fat flaps. All were successful, the results were satisfied. The method and the device of the operation are described in detail. The advantages of the technique are discussed.

[Relation of the changes in hemorheologic indices and the site and size of cerebral infarction]

According to the CT findings, 83 cases of cerebral infarction were divided into two groups. One group consisted of cases with occlusion of the cerebral arterial main trunks and the other of those with occlusion of the penetrating arteries. The HCT and the whole blood viscosity were higher in the former group, whereas the rate of platelet aggregation was higher in the latter group. These results suggested that the physiopathology involved in the formation of the large cerebral infarction in the cerebral cortex and subcortex was different from that of the small infarction in the deep cerebral structures. Besides, it was found that the blood viscosity has positive relationship with the size of the cerebral infarction in the former group. It was presumed that the HCT and the blood viscosity should be reduced immediately for treating the larger cerebral infarction, but to lower the rate of platelet aggregation for treating the small infarction in the deep cerebral structures would be of benefit.

Experience using microvascular anastomotic rings for the transplantation of 20 free flaps

A new microvascular anastomosis technique was employed with success in 1985-1986 with the result of 18 free-flap survivals and 2 failures. The rate of success in microvascular anastomoses was 90.5 percent (38 of 42). The advantages of this technique are its simplicity, convenience, and safety, and it may shorten the duration of the operation. Our experience in using vascular anastomotic rings is presented.

Identical linkage and cooperativity of oxygen and carbon monoxide binding to Octopus dofleini hemocyanin

Employment of high-precision thin-layer methods has enabled detailed functional characterization of oxygen and carbon monoxide binding for (1) the fully assembled form with 70 binding sites and (2) the isolated chains with 7 binding sites of Octopus dofleini hemocyanin. The striking difference in the cooperativities of the two ligands for the assembled decamer is revealed through an examination of the binding capacities and the partition coefficient, determined as functions of the activities of both ligands. A global analysis of the data sets supported a two-state allosteric model assuming an allosteric unit of 7. Higher level allosteric interactions were not indicated. This contrasts to results obtained for arthropod hemocyanins. Oxygen and carbon monoxide experiments performed on the isolated subunit chain confirmed the presence of functional heterogeneity reported previously [Miller, K. (1985) Biochemistry 24, 4582-4586]. The analysis shows two types of binding sites in the ratio of 4:3.

An analytic solution to the Monod-Wyman-Changeux model and all parameters in this model

Starting from the Monod-Wyman-Changeux (MWC) model (Monod, J., J. Wyman, and J. P. Changeux. 1965. J. Mol. Biol. 12:88-118), we obtain an analytical expression for the slope of the Hill plot at any ligand concentration. Furthermore, we derive an equation satisfied by the ligand concentration at the position of maximum slope. From these results, we derive a set of formulas which allow determination of the parameters of the MWC model (kR, C, and L) from the value of the Hill coefficient, nH, the ligand concentration at the position of maximum slope [( A]0), and the value of nu/(n-nu) at this point. We then outline procedures for utilizing these equations to provide a "best fit" of the MWC model to the experimental data, and to obtain a refined set of the parameters. Finally, we demonstrate the applicability of the technique by analysis of oxygen binding data for Octopus hemocyanin.

A reexamination of the reported B----Z DNA transition in nucleosomes reconstituted with poly(dG-m5dC).poly(dG-m5dC)

Polynucleosomes with poly(dG-m5dC).poly(dG-m5dC) have been reconstituted, and well-defined nucleosome core particles from these have been prepared. Upon addition of MgCl2 to the levels used to induce the B to Z transition in this highly methylated DNA, significant changes in the circular dichroism spectrum are observed in solutions of these particles. However, such core particles also exhibit a noticeable instability when compared to chicken erythrocyte core particles under the same conditions. The change in circular dichroism can be entirely accounted for on the assumption that only free nucleotide, released by core particle dissociation, undergoes the B----Z transition. Therefore, no evidence has been found for "Z nucleosomes" in these solutions. In fact, the histone-DNA interaction in the nucelosome seems to partially inhibit the B to Z transition of the DNA. The analysis of our results is consistent with a model in which all of the DNA that remains bound to the histone octamer retains the B form.