[Relationship between smoking and the risk of morbidity of chronic obstructive pulmonary diseases among residents aged 30 years and above in Sichuan Province: a prospective study]

Objective: To investigate the morbidity of chronic obstructive pulmonary diseases (COPD) in residents aged 30 years and above in Sichuan Province, and analyze the effect of smoking on the risk of morbidity on COPD. Methods: From 2004 to 2008, people were randomly selected from Pengzhou, Sichuan Province. All the local people aged 30-79 years were asked to receive questionnaire survey, physical examination and pulmonary function testing, and long-term follow-up to determine the morbidity of COPD. Cox proportional hazard regression model was used to analyze the relationship between smoking and COPD. Results: In 46 540 participants, the current smoking rates were 67.31% in males and 8.67% in females, there were 3 101 new cases of COPD, with a cumulative incidence of 6.66%. Adjusted for age, gender, occupation, marriage, income level, educational level, BMI, daily total physical activity, current cooking frequency, whether there was smoke exhaust device at present and frequency of passive smoking exposure, multivariate Cox proportional hazard regression analysis showed that compared with the non-smoking population, current smoking and quitting smoking increased the risk of COPD, with HR of 1.42 (95%CI:1.29-1.57) and 1.34 (95%CI:1.16-1.53). Compared with people who never or occasionally smoke, the risk of morbidity on COPD increased with the increase of average daily smoking volume, mixed smoking at present, mixed smoking at the beginning increased the risk of COPD, with HR of 1.79 (95%CI: 1.42-2.25) and 2.12 (95%CI: 1.53-2.92), started smoking at the age of <18 years old and ≥18 years old increased the risk of COPD, with HR of 1.61 (95%CI:1.43-1.82) and 1.34 (95%CI: 1.22-1.48), inhaling into the mouth, throat and lung during smoking increased the risk of COPD, with HR of 1.30 (95%CI: 1.16-1.45), 1.63 (95%CI: 1.45-1.83) and 1.37 (95%CI: 1.21-1.55). Adjusted for multiple confounding factors and adjusted for regression dilution bias, the average daily smoking volume, the age of starting smoking and the depth of smoking inhalation had an impact on the incidence of COPD, and the gender difference was particularly prominent. Conclusions: Smoking increased the risk of morbidity on COPD, which was related to the average daily smoking volume, the type of smoking, the age of starting smoking and the depth of smoking inhalation. Tobacco control should comprehensively consider the specific characteristics of smoking, so as to prevent COPD.

Antigen Presentation and Proteome Study of Exosomes Secreted by Co-Culture of Macrophages and Talaromyces marneffei

It is known that intracellular pathogens interact and react with the cellular immune system through exosomes produced by macrophages. This study aimed to determine whether co-culture of macrophages and Talaromyces marneffei induces exosomes and leads to immune responses. T. marneffei was incubated to collect conidia, co-cultured with human macrophages, which then induced exosomes. In cellular experiments, after extraction and purification, the exosomes were then observed by electron microscopy and detected by flow cytometry and mass spectrometry. In animal experiments, flow cytometry and enzyme-linked immunosorbent assay were used to examine whether exosomes were antigenpresenting. The results showed that purified exosomes produced a pro-inflammatory response and stimulated production of TNF-α in non-fungal-treated macrophages. Protein mass spectrometry analysis of exosomes also indicated their potential ability to activate the internal immune response system and the pro-inflammatory response. Translation and ribosomes were the most abundant GO terms in proteins, and the most relevant KEGG pathway was the biosynthesis of secondary metabolites. Furthermore, in vivo experiments revealed that exosomes induced activation of lymphocytes and increased expression of TNF-α and IL-12 in the lung, mediastinum, and spleen area. In conclusion, exosomes can be released by co-culture of T. marneffei and macrophages, having antigen-presenting functions, promoting macrophage inflammation, and initiating adaptive immune responses. These processes are inextricably linked to the translation of secondary metabolites, ribosomes and biosynthesis.

Comprehensive Effects of Suppression of MicroRNA-383 in Human Bone-Marrow-Derived Mesenchymal Stem Cells on Treating Spinal Cord Injury

BACKGROUND/AIMS

Transplantation of bone-marrow-derived mesenchymal stem cells (MSCs) promotes neural cell regeneration after spinal cord injury (SCI). Recently, we showed that suppression of microRNA-383 (miR-383) in MSCs increased the protein levels of glial cell line derived neurotrophic factor (GDNF), resulting in improved therapeutic effects on SCI. However, the overall effects of miR-383 suppression in MSCs on SCI therapy were not determined yet. Here, we addressed this question.

METHODS

We used bioinformatics tools to predict all miR-383-targeting genes, confirmed the functional bindings in a dual luciferase reporter assay. The effects of alteration of candidate genes in MSCs on cell proliferation were analyzed by MTT assay and by Western blotting for PCNA. The effects on angiogenesis were assessed by HUVEC assay. The effects on SCI in vivo were analyzed by transplantation of the modified MSCs into nude rats that underwent SCI.

RESULTS

Suppression of miR-383 in MSCs not only upregulated GDNF protein, but also increased vascular endothelial growth factor A (VEGF-A) and cyclin-dependent kinase 19 (CDK19), two other miR-383 targets. MiR-383-suppression-induced increases in CDK19 resulted in a slight but significant increase in MSC proliferation, while miR-383-suppression-induced increases in VEGF-A resulted in a slight but significant increase in MSC-mediated angiogenesis.

CONCLUSIONS

Upregulation of CDK19 and VEGF-A by miR-383 suppression in MSCs further improve the therapeutic potential of MSCs in treating SCI in rats.

Suppression of MicroRNA-383 Enhances Therapeutic Potential of Human Bone-Marrow-Derived Mesenchymal Stem Cells in Treating Spinal Cord Injury via GDNF

Background/Aims: Transplantation of bone-marrow-derived mesenchymal stem cells (MSCs) has been used to treat spinal cord injury (SCI) to enhance tissue repair and neural cell regeneration. Glial cell line derived neurotrophic factor (GDNF) is an identified neural growth and survival factor. Here, we examined whether modification of GDNF levels in MSCs may further increase the potential of MSCs in promoting neural cell regeneration and subsequently the therapeutic outcome. Methods: We examined the mRNA and protein levels of GDNF in human MSCs by RT-qPCR and Western blot, respectively. Bioinformatics analyses were done to predict microRNAs (miRNAs) that target GDNF in MSCs. The functional binding of miRNAs to GDNF mRNA was examined by a dual luciferase reporter assay. MSCs were transduced with adeno-associated virus (AAV) carrying null or antisense for miR-383 (as-miR-383), which were transplanted into nude rats that underwent SCI. The intact tissue, cavity volume, and recovery of locomotor activity were assessed. Results: MSCs expressed very low GDNF protein, but surprisingly high levels of GDNF mRNA. Bioinformatics analyses showed that miR-383 inhibited protein translation of GDNF, through binding to the 3’-UTR of the GDNF mRNA. MSCs transduced with AAV-as-miR-383 further increased the intact tissue percentage, decreased cavity volume, and enhanced the recovery of locomotor activity in nude rats that underwent SCI, compared to MSCs. Conclusions: Suppression of miR-383 may increase the therapeutic potential of human bone-marrow-derived MSCs in treating SCI via augmentation of GDNF protein levels.

[Association of RTN4 gene rs2864052 and rs6545468 with the susceptibility of nasopharyngeal carcinoma in Guangxi Zhuang population]

Objective:To study the relationship of the polymorphism of RTN4 gene rs2864052 and rs6545468 and haplotype with the susceptibility of nasopharyngeal carcinoma in Guangxi Zhuang population. Method:The polymorphism of Nogo gene (rs2864052,rs6545468) and haplotype were analyzed using the method of single-base extension PCR and DNA sequencing in 282 cases of nasopharyngeal carcinoma (NPC) and 199 healthy persons (control group) in Guangxi Zhuang Autonomous Region. Result:There were no differences between the NPC's patients and controls in the genotype and allele frequencies of RTN4 gene rs2864052 site,or rs6545468 site. The frequency of AG haplotype in the NPC's patients was significantly lower than in the controls(P=0.004, OR=0.14,95%CI=0.31-0.68). Conclusion:The haplotype AG of RTN4 gene rs2864052 and rs6545468 sites may reduce the risk of nasopharyngeal carcinoma in Guangxi Zhuang population.

Regulatory effect of miRNA on multi-directional differentiation ability of mesenchymal stem cell in treatment of osteoporosis

This study was designed to evaluate the effect of miRNA acting in regulating multi-directional differentiation ability of mesenchymal stem cell in treatment of osteoporosis (OP), with the aim of finding a new idea and approach for clinical treatment of OP. Estrogen deficiency-induced OP mice model was established by means of ovariectomy (OVX). Additionally, a sham group was set up for control. Bone Marrow Mesenchymal Stem Cells (BMMSCs) of OVX group (O/BMMSCs) and BMMSCs of sham group (S/BMMSCs) were separately cultured. Then surface markers of BMMSCs were detected. Multi-directional differentiation ability was identified in the two groups by giving cells targeted induced stimulation. It was found that the bone trabecula, bone density and bone volume fraction of distal femoral metaphysis in the OVX group were much lower than those of the sham group. Moreover, trabecular bone space in the OVX group became larger; O/BMMSCs and S/BMMSCs both had normal expression of surface markers as well as potentials of osteogenic and adipogenic differentiation; O/BMMSCs had a weaker osteogenic capability but a stronger adipogenic capability than S/BMMSCs. All the findings suggest that the regulatory effect of miRNA on multi-directional differentiation ability plays a vital role in the treatment of OP, and there is a close correlation between them; deficiency or functional defect of BMMSCs can result in the occurrence of OP.

Actinomycin D inhibits cell proliferations and promotes apoptosis in osteosarcoma cells

Actinomycin D (ActD), a well known transcription inhibitors, has been widely reported to induce cell apoptosis in several types of tumor cells by inhibiting the anti-apoptotic gene transcriptions. However, how ActD affects osteosarcoma cells survival and its molecular mechanism is currently unclear. In the present study, results of proliferation assays and Hoechst stainings suggested that MG63 human osteosarcoma cells showed impaired cell proliferations and significant apoptosis after ActD treatment. Moreover, biochemical results showed that cleaved caspase-3 is gradually increased with the increasing ActD concentrations and treated times. Importantly, results of western blots indicated that protein levels of cyclin factors, such as cyclin A, D1 and E, were all reduced after ActD treatment. And ActD treatments may inhibit mRNA transcription levels of these cyclin factors, which may finally lead to cell cycle arrest and consequently apoptosis. The present study have revealed a novel mechanism by which ActD inhibits osteosarcoma cell proliferations and induces apoptosis, and will provide an useful clue to chemotherapy in future treatment of osteosarcoma.

Promotion of peripheral nerve regeneration of a peptide compound hydrogel scaffold

BACKGROUND

Peripheral nerve injury is a common trauma, but presents a significant challenge to the clinic. Silk-based materials have recently become an important biomaterial for tissue engineering applications due to silk's biocompatibility and impressive mechanical and degradative properties. In the present study, a silk fibroin peptide (SF16) was designed and used as a component of the hydrogel scaffold for the repair of peripheral nerve injury.

METHODS

The SF16 peptide's structure was characterized using spectrophotometry and atomic force microscopy, and the SF16 hydrogel was analyzed using scanning electron microscopy. The effects of the SF16 hydrogel on the viability and growth of live cells was first assessed in vitro, on PC12 cells. The in vivo test model involved the repair of a nerve gap with tubular nerve guides, through which it was possible to identify if the SF16 hydrogel would have the potential to enhance nerve regeneration. In this model physiological saline was set as the negative control, and collagen as the positive control. Walking track analysis and electrophysiological methods were used to evaluate the functional recovery of the nerve at 4 and 8 weeks after surgery.

RESULTS

Analysis of the SF16 peptide's characteristics indicated that it consisted of a well-defined secondary structure and exhibited self-assembly. Results of scanning electron microscopy showed that the peptide based hydrogel may represent a porous scaffold that is viable for repair of peripheral nerve injury. Analysis of cell culture also supported that the hydrogel was an effective matrix to maintain the viability, morphology and proliferation of PC12 cells. Electrophysiology demonstrated that the use of the hydrogel scaffold (SF16 or collagen) resulted in a significant improvement in amplitude recovery in the in vivo model compared to physiological saline. Moreover, nerve cells in the SF16 hydrogel group displayed greater axon density, larger average axon diameter and thicker myelin compared to those of the group that received physiological saline.

CONCLUSION

The SF16 hydrogel scaffold may promote excellent axonal regeneration and functional recovery after peripheral nerve injury, and the SF16 peptide may be a candidate for nerve tissue engineering applications.

Association of estrogen receptor alpha gene polymorphisms and risk of fracture

The association between estrogen receptor alpha (ESR1) gene polymorphisms and risk of fracture is still controversial and ambiguous. The objective of this study was to evaluate the effect of PvuII polymorphisms of the ESR1 gene on fracture risk in Chinese patients. A population-based control study of elderly subjects was conducted in 120 fracture patients and 120 controls. The PvuII pp genotype of the ESR1 gene was determined by using a polymerase chain reaction-restriction fragment length polymorphism assay. There was no relationship between ESR1 gene PvuII polymorphism and fracture risk. When stratifying by fracture type, it was found that vertebral fracture cases had a significantly higher frequency of the PvuII pp genotype (odds ratio=2.00, 95% confidence interval=1.03, 3.88; p=0.04) than controls. This study suggested that there was a modest but statistically significant association between the PvuII pp genotype of the ESR1 gene and vertebral fracture in Chinese patients. The molecular mechanism underlying this association needs further study.

Trypanosoma congolense infections: MHC class II-restricted immune responses mediate either protection or disease, depending on IL-10 function

BALB/c mice are highly susceptible and C57BL/6 relatively resistant to Trypanosoma congolense infections. Here we show that relatively resistant wild-type B6 mice infected with T. congolense survive significantly longer (> 200 days) than infected major histocompatibility complex (MHC) class II-deficient B6 mice (approximately 50 days). We also show that blocking of the interleukin-10 (IL-10) receptor induces early death of wild-type B6 mice infected with T. congolense (approximately 10 days), but does not affect the survival of infected MHC class II-deficient B6 mice. We conclude that MHC class II-restricted immune responses mediate protection and, when IL-10 function is impaired, MHC class II-restricted immune responses mediate early mortality in otherwise resistant B6 mice. Thus, in T. congolense infections, MHC class II-restricted immune responses mediate either protection or disease, depending on IL-10 function.

Experimental African trypanosomiasis: lack of effective CD1d-restricted antigen presentation

BALB/c mice are highly susceptible to African trypanosomiasis, whereas C57BL/6 mice are relatively resistant. Other investigators have reported that the synthesis of IgG antibodies to purified membrane form of variant surface glycoprotein (mfVSG) of Trypanosoma brucei is CD1 restricted. In this study, we examine the role of the CD1d/NKT cell pathway in susceptibility and resistance of mice to infection by African trypanosomes. Administration of anti-CD1d antibodies to Trypanosoma congolense-infected BALB/c mice neither affects the parasitemia nor the survival time. Correspondingly, CD1d(-/-) and CD1d(+/+) BALB/c mice infected with T. congolense or T. brucei show no differences in either parasitaemia or survival time. The course of disease in relative resistant C57BL/6 mice infected with T. congolense is also not affected by the absence of CD1d. Parasitaemia, survival time, and plasma levels of IgG2a and IgG3 parasite-specific antibodies in infected CD1d(-/-) C57BL/6 are not different from those of infected CD1d(+/+) C57BL/6 mice. We conclude that CD1d-restricted immune responses do not play an important role in susceptibility/resistance of mice infected with virulent African trypanosomes. We speculate that virulent trypanosomes have an evasion mechanism that prevents the induction of a parasite-specific, CD1d-restricted immune response by the host.

Chemistry and antioxidative factors in rosemary and sage

Rosemary and sage are common spices used in food. In our recent search of cancer chemopreventive agents from spices, the alcohol extracts of rosemary and sage showed strong antumorigenic activities. Rosemary and sage extracts contain active antioxidative factors such as phenolic diterpenes, flavonoids and phenolic acids. Here we discuss chromatographic methods used to separate and purify compounds from these spices and MS and NMR spectrometry to identify the isolated compounds. Several new compounds isolated from sage were determined to be 6-O-caffeoyl-beta-D-fructofuranosyl-(2-->1)-beta-glucopyranoside, 1-O-caffeoyl-beta-D-apiofuranosyl-(1-->6)-beta-D-glucopyranoside, 1-O-p-hydroxybenzoyl-beta-D-apiofuranosyl-(1-->6)-beta-D-glucopyranoside, 1-O-(3-methyl-2,3,4-trihydroxybutyl)-6-O-feruloyl-beta-D-glucopyranoside, 4-hydroxyacetophenone 4-O-[5-O-(3,5-dimethoxy-4-hydroxybenzoyl)-beta-D-apiofrunosyl]-(1-->2)-beta-D-glucopyranoside and 1-O-[2-hydroxy-5-(2-hydroxyethyl)phenyl]-6-O-trans-caffeoyl-beta-D-glucopyranoside.

High-energy collision-induced dissociation of ceramide ions from permethylated glycosphingolipids

Ceramide fragments from permethylated glycosphingolipids (GSLs) were studied by highenergy collision-induced dissociation (CID). In comparison with ceramlde fragments of underivatized GSLs, many more product ions including charge-remote fragment ions were observed. These ions provided detailed structural information on the ceramides. The relative intensity and the mass interval between the L and M ions were used to assign the position of the double bond. The position of the hydroxyl group was assigned with the Ln and K ions. Because the ceramide fragments and not the pseudomolecular ions were selected as the precursor ions, the size of GSLs had little effect on the quality of the product ion spectra. The sensitivity of this approach was in the range of picomoles.

Electron microscopy and hydrodynamic properties of blood clotting factor V and activation fragments of factor V with phospholipid vesicles

The electron microscopic and hydrodynamic properties of factor V and factor Va-vesicle complexes were determined. Images of negatively stained factor V bound to vesicles showed the protein as a relatively large globular domain (9.5 nm diameter) connected to the membrane through a narrow protein region 0.5-3 nm in length. This connecting region was not always visible and was measured as the distance between the globular region and the apparent vesicle edge. Factor V protein alone usually appeared as two connected globular regions of 10.2 and 6.5 nm diameter. The two-domain protein structure appeared consistent with both the image of factor V alone and bound to the membrane. Factor V had no biological activity in a phospholipid-free prothrombinase assay system used. The proteolytically activated form of factor V generated by digestion with thrombin (factor Va) was at least 30,000 times more active. The electron microscopic images of factor Va-vesicle complexes showed a smaller protein that was more closely associated with the vesicle surface than was factor V. The light chain (Mr about 80,000) component of factor Va also bound to the surface of the vesicles and appeared to be largely external to the membrane. Protein-induced hydrodynamic radius changes for the factor V-vesicle and factor Va-vesicle complexes were 12.8 and 6.3 nm, respectively. The images observed in the electron microscope were used to calculate protein-induced radius changes. Comparison of these values with the experimentally determined hydrodynamic radius changes showed approximate agreement for factor Va-membrane complexes. However, the images of factor V-vesicle complexes suggested smaller hydrodynamic radius changes than were actually observed.

Stopped-flow studies of myelin basic protein association with phospholipid vesicles and subsequent vesicle aggregation

When mixed with vesicles containing acidic phospholipids, myelin basic protein causes vesicle aggregation. The kinetics of this vesicle cross-linking by myelin basic protein was investigated by using stopped-flow light scattering. The process was highly cooperative, requiring about 20 protein molecules per vesicle to produce a measurable aggregation rate and about 35 protein molecules per vesicle to produce the maximum rate. The maximum aggregation rate constant approached the theoretical vesicle-vesicle collisional rate constant. Vesicle aggregation was second order in vesicle concentration and was much slower than protein-vesicle interaction. The highest myelin basic protein concentration used here did not inhibit vesicle aggregation, indicating that vesicle cross-linking occurred through protein-protein interactions. In contrast, poly(L-lysine)-induced vesicle aggregation was easily inhibited by increasing peptide concentrations, indicating that it did cross-link vesicles as a peptide monomer. The myelin basic protein:vesicle stoichiometry required for aggregation and the low affinity for protein dimerization suggested that multiple protein cross-links were needed to form a stable aggregate. Stopped-flow fluorescence was used to estimate the kinetics of myelin basic protein-vesicle binding. The half-times obtained suggested a rate constant that approached the theoretical protein-vesicle collisional rate constant.

Calcium effects on prothrombin and its reaction with bifunctional alkylating reagents

Monodisperse bovine prothrombin was prepared and its molecular states under several conditions examined. The protein showed no tendency to self-associate in the absence of calcium. Calcium (4 mM) caused small increases in the apparent molecular weight of the protein which may or may not represent protein dimerization with very low affinity. The allowed conclusion was that calcium-induced prothrombin dimerization is minimal up to protein concentrations of many mg/ml. Calcium-induced protein shape changes did not measurably alter the protein diffusion constant. A bifunctional alkylating reagent did produce extensive calcium-dependent prothrombin crosslinking. Prothrombin dimers formed by the crosslinking agent were not a measure of the state of native prothrombin.

Kinetic and hydrodynamic analysis of blood clotting factor V-membrane binding

The kinetics and hydrodynamic properties of factor V-membrane interaction were characterized. Factor V bound to membranes containing acidic phospholipids with a high collisional efficiency. For membranes of 20% phosphatidyl-serine-80% phosphatidylcholine, an association rate constant of (1.13 +/- 0.10) X 10(8) M-1 s-1 was obtained. These membranes contained about 20 factor V binding sites per vesicle of 3.6 X 10(6) daltons. This association rate represented about a 30% collisional efficiency. Dissociation of factor V was measured by a fluorescence energy transfer method with a dissociation rate constant of 0.0055 s-1 at 10 degrees C. The equilibrium dissociation constant for binding to these membranes at 10 degrees C and 0.14 M ionic strength was 5 X 10(-11) M. Ionic strength, pH, calcium, and charge density in the membrane had large effects on the rate of factor V-membrane dissociation, indicating a strongly ionic interaction between protein and membrane. In contrast, the association rate was nearly insensitive to ionic strength. The membrane-binding properties were relatively unchanged after thrombin digestion of factor V or after long-term protein storage which resulted in loss of procoagulant activity. Other proteins of the prothrombinase reaction greatly decreased the rate of factor Va-membrane dissociation. At protein saturation, factor V increased the hydrodynamic radius of phospholipid vesicles by 11.4 nm. In contrast, factor Va increased the hydrodynamic vesicle radius by only about 5 nm. The mass of membrane-bound protein was comparable for both proteins.

Effect of chymosin action on the hydrodynamic diameter of casein micelles

Quasi-elastic light scattering shows an initial decrease of about 5 nm in the hydrodynamic radius of casein micelles after adding chymosin, assuming the decrease to be equal for all micelles. This is consistent with the hypothesis that casein micelles have a hairy outer layer that is partly made up of the caseino-macropeptide part of kappa casein.

Deglycosylated prothrombin fragment 1. Calcium binding, phospholipid interaction, and self-assocation

The carbohydrate portion of prothrombin fragment 1 has been removed by fluorolysis in anhydrous HF. The deglycosylated protein retains its calcium- and membrane-binding properties. The slow, calcium-dependent protein transition monitored by changes in intrinsic protein fluorescence remains intact for the aglycoprotein. Calcium-dependent protein-membrane binding is also observed and can be quantitatively reversed with EDTA. The major alteration resulting from carbohydrate removal is the degree of protein self-association. Both the normal and deglycosylated proteins undergo a rapid self-association which approaches a dimer in the presence of calcium. This self-association is independent of the slow change in intrinsic fluorescence. The deglycosylated protein then undergoes a secondary self-association with kinetics identical with the fluorescence change. This secondary self-association also occurs on the membrane surface. This suggests that the calcium-dependent conformational change exposes a site on the protein which functions in secondary self-association. The carbohydrate apparently masks this site in the native molecule.

High concentration active enzyme centrifugation: analysis of active polymeric forms at up to 10 000-fold higher concentrations than with conventional methods

This paper describes the theoretical basis, experimental technique, and experimental evaluation of a new method of analysis called "high concentration active enzyme centrifugation". It extends by up to four orders of magnitude the upper concentration limits at which the technique of "active enzyme centrifugation" can be used for analysis of enzyme structure. This new theory is largely based on certain properties of Gaussian curves which we have described in previous publications [Wei, G.J., & Deal, W.C., Jr. (1976) Anal. Biochem. 75, 113-121; Anal. Biochem. (1978) 87, 433-446]. One of the most important aspects of this development is that it extends the concentration range upward so that experiments can be performed on enzymes in the active polymeric forms corresponding to their in vivo states. Furthermore, this expansion includes the range in which most enzymes go through all their association-dissociation transitions from one polymeric form to another. Hence, the method can be used to define the various concentration-dependent transitions and also to ascertain which of the various polymeric forms of an enzyme are active, under various conditions. This method also retains the many favorable characteristics inherent in the active enzyme centrifugation technique. In studies with lactate dehydrogenase, the results from this method of band sedimentation were identical within experimental error (about 1.5%) with results from conventional boundary sedimentation velocity studies.

Determination of polymer size distribution by combination of quasielastic light scattering and band transport: Evaluation of the effect of diffusion

In this paper we report a computer simulation study of the effect of diffusion on the size distribution obtained by combining light scattering with isokinetic band sedimentation or electrophoresis. We find that, under typical experimental conditions, the method yields reasonably accurate size distributions for samples of particles greater than 10 nm radius. However, caution should be exercised in interpreting the results for smaller particles, for which the distortion due to diffusion can be considerable.