Modulation of the redox potential of the [Fe(SCys)(4)] site in rubredoxin by the orientation of a peptide dipole

Rubredoxins (Rds) may be separated into two classes based upon the correlation of their reduction potentials with the identity of residue 44; those with Ala44 have reduction potentials that are approximately 50 mV higher than those with Val44. The smaller side chain volume occupied by Ala44 relative to that occupied by Val44 has been proposed to explain the increase in the reduction potential, based upon changes in the Gly43-Ala44 peptide bond orientation and the distance to the [Fe(SCys)(4)] center in the Pyrococcus furiosus (Pf) Rd crystal structure compared to those of Gly43-Val44 in the Clostridium pasteurianum (Cp) Rd crystal structure. As an experimental test of this hypothesis, single-site Val44 <--> Ala44 exchange mutants, [V44A]Cp and [A44V]Pf Rds, have been cloned and expressed. Reduction potentials of these residue 44 variants and pertinent features of the X-ray crystal structure of [V44A]Cp Rd are reported. Relative to those of wild-type Cp and Pf Rds, the V44A mutation in Cp Rd results in an 86 mV increase in midpoint reduction potential and the [A44V] mutation in Pf Rd results in a 95 mV decrease in midpoint reduction potential, respectively. In the crystal structure of [V44A]Cp Rd, the peptide bond between residues 43 and 44 is approximately 0.3 A closer to the Fe center and the hydrogen bond distance between the residue 44 peptide nitrogen and the Cys42 gamma-sulfur decreases by 0.32 A compared to the analogous distances in the wild-type Cp Rd crystal structure. The results described herein support the prediction that the identity of residue 44 alone determines whether a Rd reduction potential of about -50 or 0 mV is observed.

Bipartite modular structure of intrinsic, RNA hairpin-independent termination signal for phage RNA polymerases

The phage SP6 RNA and T7 RNA polymerases, which are closely related to each other, intrinsically stop at two signals in the Escherichia coli rrnB terminator t1 through different mechanisms. The downstream signal functioned without an RNA secondary structure formation, in which the signal was still active when separated from the upstream, hairpin-forming signal, and IMP incorporation enhanced its efficiency. The sequence from -15 to -1 was essential for the downstream, hairpin-independent termination (at -1). The results of SP6 transcription with heteroduplex templates and ribonucleotide analogs suggested that the downstream signal consists of two functionally different modules. The effects of iodo-CMP or IMP incorporation into RNA on termination efficiency were not sensitive to incorporation at -9 and upstream, but they were reactive to incorporation at -6 and -2, as reflected by strong iodo-rC:dG and weak rI:dC base pairing. Thus, the downstream module (from -8 approximately -6 to -1) appears to facilitate the release of RNA. Mismatches in the templates at -6 to +1 allowed for efficient termination, unlike those upstream of the sequence. The upstream module (from -15 to -9 approximately -7) functions as a duplex. Pausing of the SP6 elongation complex at the termination site was detected when RNA release was suppressed by the incorporation of 5-bromo-UMP, and it was dependent on the upstream module. Results of single-round SP6 transcriptions using 3'-deoxynucleotides and immobilized templates indicated that RNA was not released from the elongation complexes halted at the termination site on the template variants carrying mutations in the upstream or downstream module, whereas such complexes on the wild type template were dissociated. Thus, halting or simple pausing was not sufficient for termination even when the downstream module was intact. The upstream module appears to mediate such conformation change necessary for termination.

Effect of plasminogen activators on human recombinant apolipoprotein(a) having the plasminogen activation cleavage site

The serine-proteinase domain in human apolipoprotein(a) [apo(a)] and plasminogen exhibit 89% sequence identity including the catalytic triad. Cleavage of the Arg(561)-Val(562) activation site in plasminogen by either tissue- or urokinase-type plasminogen activator results in formation of the fibrinolytic enzyme plasmin. Apo(a) does not contain measurable amidolytic activity nor can it be activated by plasminogen activators. It has been suggested that the latter finding might be explained by the substitution of the plasminogen Arg-Val activation site by Ser-Ile in apo(a). To investigate if introduction of the Arg-Val activation site in apo(a) might result in sensitivity towards plasminogen activators, we expressed wild-type and Arg-Val mutant recombinant apo(a) [r-apo(a)] in human embryonic kidney and hepatocyte cell lines. Free r-apo(a) and lipoprotein-like particles [r-Lp(a)] were obtained in the culture supernatants of transfected 293 and HepG2 cells, respectively. Incubation of mutant r-apo(a)/r-Lp(a) with plasminogen activators produced neither plasmin-like activity nor cleavage at the Arg-Val activation site, even in the presence of various stimulators of plasminogen activation. Our data suggest that the high selectivity of activators for plasminogen activation requires interactions with regions in plasminogen distant from the activation disulfide loop which are not present in apo(a).

The effect of region of interest selection on dual energy X-ray absorptiometry measurements of the calcaneus in 55 post-menopausal women

Bone mineral density (BMD) of the calcaneus was assessed by dual energy X-ray absorptiometry (DXA) in four different regions of the calcaneus in 20 pre-menopausal and 55 post-menopausal women, none of whom were on treatment or suffering from conditions affecting bone. The total body option in the small animal software package of a Lunar DPX-L bone densitometer was used. The precision of the technique (%CV) varied from 0.7 to 2.2% depending on the region scanned. For post-menopausal women, BMD results in the mid and posterior parts of the calcaneus varied by < 7% while BMD in the anterior region was about 20% lower. DXA of the calcaneus was compared with measurements at the spine (L2-L4) and hip (femoral neck) and changes with age were estimated from cross-sectional data. BMD of the calcaneus was significantly reduced in 28 post-menopausal women with low lumbar spine BMD (-2SD) compared with women with normal spine BMD. Calcaneal BMD was significantly correlated to axial BMD (r = 0.45-0.77) and to age (r = 0.45 to -0.63). For a subgroup of 33 post-menopausal women measured twice after approximately 1 year, calcaneus BMD decreased by between 1.2% and 2.5% while axial BMD showed no significant change. Unlike spine or femoral neck BMD, the decrease in calcaneus BMD was significantly greater in women with low spine BMD than in normal women, possibly indicating improved detection of skeletal changes. The optimum measurement sites for BMD in the calcaneus were within the mid or posterior part of the calcaneus or enclosing the whole posterior calcaneus. The calcaneus was shown to be a precise, sensitive and simple measurement site suitable for the assessment of osteoporosis, especially in the elderly where degenerative changes in the spine and hip can complicate BMD assessment.

R'2 measured in trabecular bone in vitro: relationship to trabecular separation

Measurement of key parameters of the microstructure of trabecular bone is critical to the study of osteoporosis and bone strength. Density based methods cannot provide this information, and give only the total amount of bone present, and not its arrangement. Magnetic resonance imaging has shown the potential to provide information related to the microarchitecture of the trabecular bone matrix. Twelve samples (8 x 8 x 8 mm3 bone cubes) were cut from sheep vertebrae such that the trabeculae ran either parallel or perpendicular to each face. Detailed measurements of the structure of these bone cubes were made by histomorphometry, and compared to R'2 and R*2 measured with a spin and gradient-echo sequence, Partially Refocused Interleaved Multiple Echo, at 1.5 Tesla. The precision of the R'2 measurement (% coefficient of variation) was 8.7+/-5.1, and 7.7+/-4.3 for R*2. Uncorrected values of R'2 and R*2 were significantly correlated to density measured by quantitative computed tomography (r = 0.87, p = 0.0005, and r = 0.90, p = 0.0002, respectively), and trabecular bone area measured by histomorphometry (r = 0.80, p = 0.002, and r = 0.83, p = 0.0008, respectively). Density correction was effected by imaging the same slice of bone in two orientations (90 degrees and 0 degrees ) to the main magnetic field. For both R'2 and R*2 there was a significant difference between measurements in the 90 degrees and 0 degrees orientations (p < 0.01). The difference between the two values was used, and termed R'2net or R*2net. The net parameters were independent of bone mass. R'2net and R*2net were significantly correlated to trabecular separation (p < 0.05) with r = -0.58 and r = -0.62, respectively. These results demonstrate the ability of magnetic resonance imaging to characterize a key measure of the trabecular microstucture. An increase in trabecular separation has important biomechanical consequences in osteoporosis. This result also strengthens the hypothesis that the sensitivity of R'2 to osteoporosis-related bone changes is due to magnetic susceptibility effects in which rapid transitions between bone and marrow create local magnetic field inhomogeneities that result in an increase in R'2 values.

Z-curve: a computer program calculating DNA helical axis coordinates for three-dimensional graphic presentation of curvature

In order to predict curvature of DNA fragments, we previously developed a computer program for simply calculating a vectorial sum of all individual roll, tilt and twist wedge angles between the nearest base pairs for a given DNA fragment [Lee et al., (1991)]. Now, a new program, called Z-curve, was developed to calculate three-dimensional coordinates of the helical center of each base pair along the DNA, using helical axis deviations from B-form DNA by wedge angles. The output file of the new program was designed to become an input file for a graphics program, Insight II. Thus, we were able to obtain three-dimensional graphic presentations of DNA helical axis curvatures of any length. It visualized spatial details of the DNA curvature, where and how much it curves, and to which direction. It also allowed calculation of the three-dimensional distance between two ends of a DNA fragment, which could provide a measure of its curvature. Here, three DNA fragments, both curved and straight, were subjected to the Z-curve and Insight II programs. The results showed that their curvature details could be visualized to the level of the base pair, whether the DNA fragments contained an oligo(A) track or not. Their estimated curvatures were consistent with the experimental results of permutation gel mobility assay.

Soluble expression of cloned phage K11 RNA polymerase gene in Escherichia coli at a low temperature

The gene 1 of the Klebsiella phage K11 encoding the phage RNA polymerase was amplified using the polymerase chain reaction of the Pfu DNA polymerase, cloned and expressed under the control of tac promoter in Escherichia coli. Although the gene was efficiently expressed in E. coli BL21 cells at 37 degrees C, most of the K11 RNA polymerase produced was insoluble, in contrast to soluble expression of the cloned T7 RNA polymerase gene. Coexpression of the bacterial chaperone GroES and GroEL genes together did not help solubilize the K11 RNA polymerase. When the temperature of cell growth was lowered, however, solubility of the K11 RNA polymerase was increased substantially. It was found much more soluble when expressed at 25 degrees C than at 30 and 37 degrees C. Thus, the cloned K11 RNA polymerase gene was expressed in E. coli mostly to the soluble form at 25 degrees C. The protein was purified to homogeneity by chromatography using DEAE-Sephacel and Affigel-blue columns and was found to be active in vitro with the K11 genome or a K11 promoter. The purified K11 RNA polymerase showed highly stringent specificity for the K11 promoter. Low-level cross-reactivity was shown with the SP6 and T7 consensus promoters, while no activity shown with the T3 consensus promoter at all.

Repression of hepatitis B virus X gene expression by hammerhead ribozymes

The X protein (HBx) of human hepatitis B virus (HBV) is a transcriptional activator protein. The HBx protein plays an important role in viral replication in HBV infected cells and the liver diseases including hepatitis, cirrhosis, and hepatocellular carcinoma (HCC). Therefore, the repression of HBx gene expression by hammerhead ribozymes may be a good way to inhibit HBV replication and cure HBV-related liver diseases. We designed two hammerhead ribozymes, RzA and RzB, to cleave target sites at nucleotides 114 and 309 in the HBx open reading frame (ORF), respectively. In vitro, RzA and RzB cleaved HBx RNAs at their target sites up to 52 and 75%, respectively; however, the disabled ribozymes (dRzs) which have mutations in the catalytic site did not cleave the target RNAs at all. When each of the ribozymes were cotransfected into HepG2 cells with HBx expression plasmid, RzA and RzB reduced the level of HBx mRNA to 40 and 57%, respectively. The transactivation activity of HBx protein was also reduced dramatically by the ribozymes. These results suggest that the hammerhead ribozymes, RzA and RzB, can be used for the gene therapy of liver diseases caused by HBV.

Stabilization of the i-motif by intramolecular adenine-adenine-thymine base triple in the structure of d(ACCCT)

The crystal structure of d(ACCCT), solved by molecular replacement, shows a four-stranded i-motif conformation, where two parallel duplexes intercalate with one another in opposite orientations. Each duplex is stabilized by hemi-protonated C-C+ base pairing between parallel strands, and a string of water molecules bridge the cytosine N4 atoms to phosphate O atoms. This structure of d(ACCCT) shows examples of reversed Hoogsteen and Watson-Crick base pairing in both intermolecular and intramolecular manners to stabilize the tetraplex. Noticeably, the four-stranded complex is further stabilized at one end by a three-base hydrogen-bonding network, in which two adenines and a thymine form four hydrogen bonds via a reverse Hoogsteen and an asymmetric adenine-adenine base pairing. The structure of d(ACCCT) shows a similar local structure to that found in the d(TAA) part of the crystal structure of d(TAACCC) and provides further structural evidence that these base arrangements are essential for stabilizing these novel DNA super-secondary structures.

In vivo MRI measurements of bone quality in the calcaneus: a comparison with DXA and ultrasound

Magnetic resonance imaging (MRI) has shown promise in the assessment of bone architecture. The precision and feasibility of MRI measurements in osteoporosis in vivo have been assessed in this study. T2' was calculated from measurements of T2 and T2* in the calcaneus of 32 postmenopausal women using a gradient-echo sequence PRIME (Partially Refocused Interleaved Multiple Echo). This sequence allows the measurement of T2 and T2* in one acquisition. In vivo measurements of bone mineral density (BMD) by dual-energy X-ray absorptiometry (DXA) were made in the calcaneus, spine and femoral neck. The ultrasound parameters broadband ultrasound attenuation (BUA) and speed of sound (SOS) were also measured in the calcaneus. These three techniques have not previously been compared in the same study population. The precision of the MRI technique was poor relative to the DXA and ultrasound techniques, with a CV of 6.9% +/- 4.4% for T2' and 5.5% +/- 3.6% for T2*. Approximately 4% of this is due to system error as determined by phantom measurements. The postmenopausal women were classified as having low BMD if they had a lumbar spine (L2-4) BMD of less than 0.96 g/cm2 (more than 2 standard deviations below normal peak bone mass). Calcaneal T2' was significantly correlated with calcaneal BMD (r = -0.79, p < 0.0001), BUA (r = -0.59, p = 0.0004) and SOS (r = -0.58, p = 0.0006). T2' was significantly different in postmenopausal women with normal BMD and those with low BMD (p < 0.01). However, the difference was of only borderline significance (p < 0.06) after adjustment for age and years since menopause.

Effects of reflection-induced retardance on the immunity of bulk optic-material current sensors

Reflection-induced phase retardance inside bulk optic-material current sensors makes the state of polarization of the light change, which reduces the immunity of the sensors against electromagnetic interference. These effects are analyzed theoretically for the first time, to our knowledge. A comparison between the theoretical analysis and the experimental results are given.

Requirement of heavy neurofilament subunit in the development of axons with large calibers

Neurofilaments (NFs) are prominent components of large myelinated axons. Previous studies have suggested that NF number as well as the phosphorylation state of the COOH-terminal tail of the heavy neurofilament (NF-H) subunit are major determinants of axonal caliber. We created NF-H knockout mice to assess the contribution of NF-H to the development of axon size as well as its effect on the amounts of low and mid-sized NF subunits (NF-L and NF-M respectively). Surprisingly, we found that NF-L levels were reduced only slightly whereas NF-M and tubulin proteins were unchanged in NF-H-null mice. However, the calibers of both large and small diameter myelinated axons were diminished in NF-H-null mice despite the fact that these mice showed only a slight decrease in NF density and that filaments in the mutant were most frequently spaced at the same interfilament distance found in control. Significantly, large diameter axons failed to develop in both the central and peripheral nervous systems. These results demonstrate directly that unlike losing the NF-L or NF-M subunits, loss of NF-H has only a slight effect on NF number in axons. Yet NF-H plays a major role in the development of large diameter axons.

Viability of E. coli cells containing phage RNA polymerase and promoter: interference of plasmid replication by transcription

Strong transcription of phage promoters often renders the host E. coli cells containing the phage RNA polymerase inviable. When expression of the phage SP6 RNA polymerase gene in one plasmid was induced in the E. coli JM109 cells, cells that bear an active SP6 promoter were inviable. When it was not induced (the polymerase was still produced in low levels), viability of the host cells and stability of the promoter-bearing plasmids depended on the orientation of the promoter with respect to that of the replication origin and on the sequence of the origin. A group of SP6 promoter-bearing plasmids (group I plasmids) that had the promoter directed towards the ColE1 replication origin, rendered the polymerase-containing host cells inviable in selective media. When the sequence of the origin was different (group II plasmids), this adverse effect was not observed. When the promoter direction was same as the replication origin and the ampicillin-resistant gene (group III plasmids), many satellites formed around the colonies on ampicillin-containing agar plates. These effects were caused by strong transcription of the phage SP6 promoter by its RNA polymerase, since they were reduced or eliminated by inserting an active terminator just downstream of the promoter. The viability of host cells and copy number of the promoter/terminator-bearing plasmids appear to be quantitatively related with efficiency of initiation and termination of the phage transcription. These systems may be useful for in vivo screening for mutant variants of the phage promoter, polymerase and terminator that are affected in their efficiency.

Effects of cigarette smoking and 12-h abstention on working memory during a serial-probe recognition task

Nicotine has been shown to affect attentional and mnemonic processes. However, whether these effects are due to changes in perceptual and/or motor aspects of the tasks is not at all clear. This study tested the hypothesis that nicotine from cigarette smoking has differential effects on perceptual and motor processes, as reflected by event-related potentials (ERPs) and reaction times (RTs), respectively, and that perceptual effects may be specific to changes in working memory. ERPs. RTs and performance accuracy were recorded from smokers and nonsmokers during a serial-probe recognition memory task in which lists of words or "memory sets" were followed by a probe word that was either in-set or out-of-set. Smokers were tested in a "smoking" and a 12-h "deprived" condition. Smoking-smokers and deprived-smokers exhibited fast RTs to in-set and out-of-set probes relative to a group of nonsmokers. They exhibited even faster RTs when the inset probe word matched the first or last item in the memory set. Thus, smokers as a group showed enhanced primacy and recency effects suggesting that smoking specifically facilitates processes related to the motor output aspects of working memory. Different effects characterized the electrophysiology. Larger P300s were recorded to in-set compared to out-of-set probes by both subject groups. Smoking smokers exhibited enhanced P300s to both types of probes. When smokers abstained for 12 h (deprived smokers), the differences in P300 amplitude were reduced but not eliminated. Smoking smokers exhibited faster P300 latencies to in-set probes, while deprived smokers showed delayed latencies relative to nonsmokers. Primacy and recency P300 effects characterized nonsmokers and deprived smokers. However, this relationship was reversed in the Smoking condition. These results support the hypotheses that nicotine has distinct effects on memory-related perceptual and motor aspects of working memory. The increase in efficiency of the memory search with nicotine is consistent with the functional role of the cholinergic system in maintaining a state "appropriate for efficient information processing."

Probing RegA/RNA interactions using electrospray ionization-fourier transform ion cyclotron resonance-mass spectrometry

The interactions of bacteriophage T4 regA protein, a unique translational regulator, with RNAs of various size and sequence were studied using electrospray ionization-Fourier transform ion cyclotron resonance-mass spectrometry. Using very gentle interface conditions, regA/RNA complexes with a 1:1 binding stoichiometry were observed for all four target RNAs studied, consistent with solution binding studies. Competitive binding of target RNAs and their degradation products with regA demonstrated that the loss of a single nucleotide resulted in a dramatic change in binding affinity in some cases. Competitive binding of regA with four target RNAs revealed similar relative binding affinity order to that suggested by previous in vitro repression experiments. The use of sustained off-resonance irradiation for collisionally induced dissociation of a regA/RNA complex suggested the potential for directly obtaining information regarding the regA binding domain.

Comparison of ultrasound and dual energy X-ray absorptiometry measurements in the calcaneus

Ultrasound measurements have been proposed as a means of providing structural information on bone but have also been shown to correlate with density. High correlation coefficients have been obtained in vitro, but are lower for in vivo work. The aim of this study was to investigate the relationship of broadband ultrasound attenuation (BUA), speed of sound (SOS) and stiffness, to bone mineral density (BMD) measured in the calcaneus at a closely matched region of interest (ROI). Measurements were made in 55 post-menopausal and 20 young, normal women. Calcaneus BMD measurements were made using an ROI (fixed by reference to external axes) to represent the area and location of the ultrasound transducers and an ROI based on anatomical markers, positioned in the posterior part of the calcaneus. BUA was significantly correlated with calcaneus BMD in the fixed ROI (r = 0.77, p < 0.0001) and the anatomical ROI (r = 0.78, p < 0.0001). Correlation of BUA with axial BMD was lower at r = 0.63, p < 0.0001 for the spine (L2-L4) and r = 0.59, p < 0.0001 for the femoral neck. Results for SOS and stiffness were very similar. From the calcaneus dual energy X-ray absorptiometry (DXA) scan images the region representing the ultrasound measurement area was found to contain cortical bone edges in 60% of cases. In 16% of scans a small part (4.5 +/- 4.0%) of the ROI measurement area fell partially outside the heel. However, there was no obvious discrepancy in the ultrasound results in the individual cases where this occurred. The correlation between calcaneus BMD and BUA was improved from r = 0.72 to r = 0.86 when scans with a cortical edge in the measurement ROI were excluded. The values for SOS were similar. In summary, BMD of the calcaneus, when closely matched to the site of ultrasound measurement shows significant correlation with ultrasound measurements. By excluding scans in which the ultrasound measurement appeared to include bone edges, correlations of approximately r = 0.86 were obtained. However, the BMD result still does not explain all of the variance in the ultrasound results.

Absence of the mid-sized neurofilament subunit decreases axonal calibers, levels of light neurofilament (NF-L), and neurofilament content

Neurofilaments (NFs) are prominent components of large myelinated axons and probably the most abundant of neuronal intermediate filament proteins. Here we show that mice with a null mutation in the mid-sized NF (NF-M) subunit have dramatically decreased levels of light NF (NF-L) and increased levels of heavy NF (NF-H). The calibers of both large and small diameter axons in the central and peripheral nervous systems are diminished. Axons of mutant animals contain fewer neurofilaments and increased numbers of microtubules. Yet the mice lack any overt behavioral phenotype or gross structural defects in the nervous system. These studies suggest that the NF-M subunit is a major regulator of the level of NF-L and that its presence is required to achieve maximal axonal diameter in all size classes of myelinated axons.

[Surgical treatment of epispadias]

OBJECTIVE

To analyse the surgical treatment of 124 cases of epispadias (incomplete 27 cases, complete 21 and complex 76).

METHOD

Leadbetter's operation was used for anti-incontinence. Urethral tightening was used in 4 cases of complete female epispadias. Penile straightening was adopted for incomplete epispadias and penile lengthening for complete and complex male epispadias.

RESULT

In 97 cases of urinary incontinence, complete continence was achieved in 73.

CONCLUSION

The orthopedic effects of external genitals were satisfactory.

[Study on the power of O/E method]

This paper addresses the methodology of calculating the power of O/E method and introduces the relevant algorithm for estimating the sample size. Based on the principles of hyporthesis testing and Poisson distribution, the power can be worked out for given sample size, baseline rate(pi 0) and the factor of increasing (gamma). The power increases with the increase in sample size, pi 0 and gamma. In shape the power is not a continuous smooth line but a zigzag line. The method illustrated in this paper can be also used for estimaging the sample size of studies on the intervention of diseases.

Phylogenetic analysis of the nef gene reveals a distinctive monophyletic clade in Korean HIV-1 cases

To study the genetic variation of the HIV-1 strains prevalent in South Korea, we analyzed the nef sequences derived from 46 HIV-1-positive individuals living in various geographic regions in Korea. Phylogenetic analysis revealed four subtypes of HIV-1: A (3 patients), B (41 patients), D (1 patient), and a type that could not be clearly classified to any known subtype (1 patient). Thirty-five of the 41 Korean subtype B isolates formed a distinct monophyletic clade that is not related to any of the international sequences from the Los Alamos Database or GenBank as of June 1997. Indeed, the presence of unique conserved sequences was identified among the Korean isolates in this Korean subtype B group. The variations in the nucleotide sequences of a majority (32 of 35) subtype B samples within the Korean clade were 1.9% to 8.8%, and amino acid sequences varied from 3.9% to 15.5%. These results suggest that HIV-1 strains currently present in South Korea might have originated from a few sources or might be developing through a certain selective pressure. This is the first report on the molecular nature of the HIV-1 infection present in South Korea.

Lipoprotein(a) isoforms display differences in affinity for plasminogen-like binding to human mononuclear cells

Binding of lipoprotein(a) (Lp(a)) to membrane proteins of the monocyte-macrophage cell lineage may be an important event in atheroma formation. Since Lp(a) with distinct apolipoprotein(a) (apo(a)) isoforms may show differences in their affinity with regard to fibrin binding, the existence of such a functional behavior in the interaction of apo(a) in Lp(a) with these cells was explored using the monocytic cell line THP-1. Lp(a) preparations containing small size apo(a) isoforms (M(r) = 450,000 to 550,000) and high molecular mass isoforms (M(r) > or = 700,000) were purified from plasmas containing > 0.35 g/L of Lp(a) obtained from subjects (n = 14) with cardiovascular atherosclerotic disease. Binding of plasminogen to THP-1 cells was performed using the method of radioisotopic dilution. For binding of Lp(a) to cells, the THP-1 monocytic cells were incubated with varying concentrations of the different Lp(a) preparations; cells were then washed and the amount of Lp(a) bound was detected with a radiolabeled polyclonal antibody directed against apo(a). Binding due to kringle interactions with lysine residues was calculated by subtracting from the total bound the amount of Lp(a) bound (approximately 10%) in the presence of 6-aminohexanoic acid. Analysis of data with the Langmuir equation indicated identical and independent (non-interacting) sites and allowed evaluation of the Kd. Binding isotherms of small size isoforms showed saturation and a high affinity (Kd = 25.8 +/- 19 nmol/L) relative to that of plasminogen (Kd = 1750 +/- 760 nmol/L). A similar difference (Kd = 17.5 +/- 7.9 nmol/L versus Kd = 600 +/- 220 nmol/L) was found when binding experiments were performed with a fibrin surface. In contrast, binding isotherms of the high molecular mass isoforms did not show saturation at the highest Lp(a) concentrations used, thus indicating a lower affinity. In conclusion, these results show that apo(a) isoforms may display polymorphism-linked functional heterogeneity with regard to cell binding, which may explain the higher association with cardiovascular risk of small size isoforms. These qualitative differences in the binding of apo(a) isoforms to fibrin or cells may modulate the cardiovascular risk associated with high levels of Lp(a).