The MTHFR 677 C/T polymorphism influences plasma levels of adhesion molecules and nitric oxide

BACKGROUND

Hyperhomocysteinemia is an independent risk factor for cardiovascular events. The T allele of 677 C/T polymorphism at the methylenetetrahydrofolate reductase (MTHFR) gene has been reported to induce mild hyperhomocysteinemia. In the present study, we investigated the relationship between this polymorphism and adhesion molecules and total nitric oxide (NOx).

METHODS

The adhesion molecules tested in the present study were soluble E-selectin (sE-selectin), vascular adhesion molecule (sVCAM), and intercellular adhesion molecule (sICAM). A total of 297 subjects had data on these atherosclerotic biomarkers and the MTHFR genotypes. The genetic effect was estimated in the multivariate regression models with adjustment of covariates. Homocysteine, folate, vitamin B6 and vitamin B12 levels were measured in 181 subjects for the test of association between the biomarkers and homocysteine levels.

RESULTS

The genotype distribution was in Hardy-Weinberg equilibrium. The sVCAM levels increased with the number of the T allele, while the NOx levels decreased with the number of the T allele. We found that the T allele was significantly associated with high sVCAM levels (p=0.002) and low NOx levels (p=0.011) in the regression models. The MTHFR genotypes were associated with homocysteine levels (p=0.031). Mild hyperhomocysteinemia (>12 micromol/L) was significantly associated with sVCAM levels (p=0.036). The NOx levels were lower in the hyperhomocysteinemia group than in the normal homocysteine group, but the difference was not significant. The genotypes were not significantly associated with either sE-selectin or sICAM.

CONCLUSIONS

The detrimental T allele exerted an additive effect to increase sVCAM and decrease NOx concentrations, which may contribute to atherosclerosis.

B-group vitamins, MTHFR C677T polymorphism and carotid intima-media thickness in clinically healthy subjects

OBJECTIVE

Plasma B-group vitamins and age may affect the carotid intima-media thickness (IMT) in subjects with different 677TT genotype of the methylenetetrahydrofolate reductase (MTHFR) gene.

DESIGN

A hospital-based cross-study.

SETTING

Genomic and Vascular Center, Changhua Christian Hospital, Changhua, Taiwan.

SUBJECTS

Five hundred and forty-one clinically healthy subjects.

INTERVENTION

Fasting plasma, homocysteine (Hcy), vitamin B(6), vitamin B(12), folate and B-mode carotid ultrasound.

RESULTS

MTHFR genotype, plasma concentrations of folate, vitamin B(6) and vitamin B(12) and age were significantly correlated to the plasma Hcy concentration. MTHFR 677TT carriers had higher concentrations of Hcy than did subjects with the CC and CT genotypes. Age, sex, body mass index and plasma Hcy were independent contributors to increase carotid IMT. However, with stratification by mean value of age and B-group vitamins concentrations, we found that at advanced age, lower plasma folate and vitamin B(12) were three risk factors involved in the enhancing effect of the MTHFR 677TT genotype on the increase of plasma Hcy and carotid IMT.

CONCLUSION

MTHFR 677TT-related carotid atherosclerosis was only identified in healthy elderly subjects with lower level of plasma folate and vitamin B(12).

SPONSORSHIP

Changhua Christian Hospital.

G-protein coupled receptors: SAR analyses of neurotransmitters and antagonists

BACKGROUND

From the deductive point of view, neurotransmitter receptors can be divided into categories such as cholinergic (muscarinic, nicotinic), adrenergic (alpha- and beta-), dopaminergic, serotoninergic (5-HT1 approximately 5-HT5), and histaminergic (H1 and H2). Selective agonists and antagonists of each receptor subtype can have specific useful therapeutic applications. For understanding the molecular mechanisms of action, an inductive method of analysis is useful.

OBJECTIVE

The aim of the present study is to examine the structure-activity relationships of agents acting on G-protein coupled receptors.

METHOD

Representative sets of G-PCR agonists and antagonists were identified from the literature and Medline [P.M. Walsh (2003) Physicians' Desk Reference; M.J. O'Neil (2001) The Merck Index]. The molecular weight (MW), calculated logarithm of octanol/water partition coefficient (C log P) and molar refraction (CMR), dipole moment (DM), E(lumo) (the energy of the lowest unoccupied molecular orbital, a measure of the electron affinity of a molecule and its reactivity as an electrophile), E(homo) (the energy of the highest occupied molecular orbital, related to the ionization potential of a molecule, and its reactivity as a nucleophile), and the total number of hydrogen bonds (H(b)) (donors and receptors), were chosen as molecular descriptors for SAR analyses.

RESULTS

The data suggest that not only do neurotransmitters share common structural features but their receptors belong to the same ensemble of G-protein coupled receptor with seven to eight transmembrane domains with their resultant dipoles in an antiparallel configuration. Moreover, the analysis indicates that the receptor exists in a dynamic equilibrium between the closed state and the open state. The energy needed to open the closed state is provided by the hydrolysis of GTP. A composite 3-D parameter frame setting of all the neurotransmitter agonists and antagonists are presented using MW, Hb and mu as independent variables.

CONCLUSION

It appears that all neurotransmitters examined in this study operate by a similar mechanism with the G-protein coupled receptors.

Oxidative stress-related alteration of the copy number of mitochondrial DNA in human leukocytes

The role of oxidative stress in the regulation of the copy number of mitochondrial DNA (mtDNA) in human leukocytes is unclear. In this study, we investigated the redox factors in plasma that may contribute to the alteration of mtDNA copy number in human leukocytes. A total of 156 healthy subjects of 25-80 years of age who exhibited no significant difference in the distribution of subpopulations of leukocytes in blood were recruited. Small-molecular-weight antioxidants and thiobarbituric acid reactive substances (TBARS) in plasma and 8-hydroxy-2'-deoxyguanosine (8-OHdG) and 4,977bp deletion of mtDNA in leukocytes were determined. The mtDNA copy number in leukocytes was determined by real-time PCR. The results showed that the copy number of mtDNA in leukocytes was changed with age in a biphasic manner that fits in a positively quadratic regression model (P = 0.001). Retinol (P = 0.005), non-protein thiols (P = 0.001) and ferritin (P = 0.004) in plasma and total glutathione in erythrocytes (P = 0.046) were the significant redox factors that correlated with the mtDNA copy number in leukocytes in a positive manner. By contrast, alpha-tocopherol levels in plasma (P = 0.001) and erythrocytes (P = 0.033) were negatively correlated with the mtDNA copy number in leukocytes. Three oxidative indices including the incidence of 4,977 bp deletion of mtDNA (P = 0.016) and 8-OHdG content in leukocytes (P = 0.003) and TBARS in plasma (P = 0.001) were all positively correlated with the copy number of mtDNA in leukocytes. Taken these findings together, we suggest that the copy number of mtDNA in leukocytes is affected by oxidative stress in blood circulation elicited by the alteration of plasma antioxidants/prooxidants and oxidative damage to DNA.

Structure-activity relationship: analyses of p-glycoprotein substrates and inhibitors

OBJECTIVE

A large number of structurally and functionally diverse compounds act as substrates or modulators of p-glycoprotein (p-gp). Some of them possess multiple drug resistance (MDR)-reversing activity, but only a small number of them have entered clinical study. In order to uncover the factors which exert a significant impact on the interaction between substrates/modulators and p-gp, we have performed structure-activity relationship (SAR) analyses, including molecular modelling, two-dimensional (2D) and three-dimensional (3D) parameter-frame-setting analysis, quantitative structure activity relationship (QSAR) analysis among substrates/modulators, as well as clinically promising MDR-reversing agents.

METHODS

The physicochemical parameters C log P, CMR and all regression equations were derived by using C log P version 4.0 and the latest CQSAR software, respectively. Molecular modelling and all other parameter calculations were performed by using HyperChem version 5.0 program, after geometry optimization and energy minimization using the AM1 semiempirical method.

RESULTS

SAR analyses indicate that MDR reversal activity is correlated with the lipophilicity (C log P), molecular weight (log Mw), longest chain (Nlc) of the molecule and the energy of the highest occupied orbital (Ehomo). In addition, the presence of a basic tertiary nitrogen atom in the structure is also an important contributor to p-gp inhibitory activity. Some separation in space is achieved for different subsets of p-gp substrates and inhibitors using Nlc, C log P and Ehomo as three independent parameters in the 3D-parameter-frame setting.

CONCLUSION

A highly effective p-gp modulator candidate should possess a log P value of 2.92 or higher, 18-atom-long or longer molecular axis, and a high Ehomo value, as well as at least one tertiary basic nitrogen atom. The results obtained may be useful in explaining drug-p-gp interactions for different compounds, including drug interactions and the development of new MDR chemosensitizers.

In vitro study of ultrasound based real-time tracking for renal stones in shock wave lithotripsy: Part II--a simulated animal experiment

PURPOSE

We have previously developed and reported an ultrasound based real-time tracking system for renal stones. In the current study we continued to verify the reliability of this tracking system by a simulated animal test.

MATERIALS AND METHODS

We used 13 prerecorded ultrasound stone trajectories to test the system. The real-time tracking system was implemented on the Litemed 9200 electrohydraulic lithotriptor (LiteMed Co., Taipei, Taiwan). An artificial stone and tap water were sealed in a balloon. The balloon was inserted into the pelvis of a pig kidney. While the kidney was affixed to and moved by a simulator, it was immersed in a specifically designed simulated animal model tank containing tap water. The stone was localized by ultrasound. The kidney was moved by the simulator according to a prerecorded stone trajectory. A total of 3,000 shock waves were delivered to the stone. For each recorded stone trajectory experiments were done under nontracking and tracking conditions. We performed tests of the fragment-to-weight ratio, which denotes the performance of a shock wave lithotriptor when fragmenting a stone.

RESULTS

The mean fragment-to-weight ratio was 55.3% +/- 25.9% in the nontracking and 100% +/- 0% in the tracking group. The difference in these 2 groups was statistically significant (paired t test p <0.01).

CONCLUSIONS

The ultrasound based real-time tracking system proved to improve the performance of a shock wave lithotriptor significantly when fragmenting stones in a simulated animal test. We believe that the tracking system would greatly reduce the number of shocks and time needed for treating renal stones.

Alterations of plasma antioxidants and mitochondrial DNA mutation in hair follicles of smokers

The effects of long-term smoking on mitochondrial DNA (mtDNA) deletions in hair follicles were investigated in subjects with different antioxidant capacity. Twenty-two male smokers with a smoking index of greater than 5 pack-years and without any known systemic diseases were recruited for this study. Forty healthy nonsmoking males were included as controls. We found that the concentrations of ascorbate and alpha-tocopherol and the activities of glutathione S-transferase (GST) and glutathione peroxidase in blood plasma were significantly decreased in smokers. The levels of glutathione and protein thiols in whole blood and the incidence of a 4,977 bp deletion of mtDNA (dmtDNA) in hair follicles were significantly increased in smokers. A significantly higher incidence of the 4,977 bp dmtDNA was found in smokers with plasma GST activity less than 5.66 U/l (OR = 7.2, P = 0.020). Using multiple covariate ANOVA and logistic regression, we found that age and low plasma GST activity were the only two risk factors for the 4,977 bp dmtDNA. These results suggest that smoking depletes antioxidants and causes mtDNA deletions and that plasma GST may play an important role in the preservation of the mitochondrial genome in tissue cells of smokers.

De novo regeneration of Scrophularia yoshimurae Yamazaki (Scrophulariaceae) and quantitative analysis of harpagoside, an iridoid glucoside, formed in aerial and underground parts of in vitro propagated and wild plants by HPLC

A protocol for de novo regeneration and rapid micropropagation of Scrophularia yoshimurae (Scrophulariaceae) has been developed. Multiple shoot development was achieved by culturing the shoot-tip, leaf-base, stem-node and stem-internode explants on Murashige and Skoog (MS) medium supplemented with 4.44 microM N6-benzyladenine (BA) and 1.07 microM alpha-naphthaleneacetic acid (NAA). Stem-node and shoot-tip explants showed the highest response (100%) followed by stem-internode (74.4%) and leaf-base (7.7%) explants. The shoots were multiplied by subculturing on the same medium used for shoot induction. Shoots were rooted on growth regulator-free MS basal medium and the plantlets were transplanted to soil and acclimatized in the growth chamber. The content of harpagoside, a quantitatively predominant iridoid glycoside, in different plant material was determined by high performance liquid chromatography (HPLC). The analysis revealed that the content of harpagoside in the aerial and underground parts of S. yoshimurae was significantly higher than the marketed crude drug (underground parts of Scrophularia ningpoensis).

In vitro study of ultrasound based real-time tracking of renal stones for shock wave lithotripsy: part 1

PURPOSE

We developed a real-time tracking system for renal stones that decreases the number of shock waves and treatment time of shock wave lithotripsy.

MATERIALS AND METHODS

Ultrasound images were analyzed to identify the renal stones. A computer software module for ultrasound image processing was developed to monitor stone location instantaneously. Another computer software module controlled generator movement in real time for tracking the stone. We used 13 ultrasound stone trajectories recorded from patients to test the system in vitro. Two tests were established to verify tracking system reliability. One test focused on improvement in the coincidence ratio, which denotes the matching extent of the stone within the effective focal area. The other test focused on improvement in the efficiency ratio, that is a decrease in the number of shocks for stone fragmentation. For each recorded stone trajectory 2 experiments were done under tracking and nontracking conditions.

RESULTS

The average coincidence and efficiency ratios plus or minus standard deviation were 79.6% +/- 9.8% and 45.0% +/- 12.7% without tracking, and 97.0% +/- 3.0% and 85.5 +/- 6.8% with tracking, respectively. All tests were statistically significant (paired t test p <0.01).

CONCLUSIONS

An ultrasound based real-time tracking system proved to be significantly helpful for in vitro lithotripsy. It appears that the tracking system may greatly decrease the number of shocks and treatment time for renal stones.

A conserved sequence block in the murine and human T cell receptor Jalpha loci interacts with developmentally regulated nucleoprotein complexes in vitro and associates with GATA-3 and octamer-binding factors in vivo

A highly conserved sequence block (CSB) located in the mouse and human T cell receptor (TCR) Jalpha loci is recognized by tissue-specific factors and up-regulates TCR alpha enhancer activity. In this study, the properties of CSB-interacting factors were further explored to decipher the function of this cis-acting element. Thymocytes corresponding to different developmental stages were found capable of forming differential CSB-nucleoprotein complexes. Pronounced changes in the CSB-complex-forming activity were observed during the transition from double-negative to double-positive thymocytes. Furthermore, we showed that transcription factors Oct-1, Oct-2 and GATA-3 interacted with CSB both in vitro, as evidenced by electrophoretic mobility shift assays, and in vivo, as demonstrated by chromatin immunoprecipitation assays in mouse thymus. Importantly, we also demonstrated that GATA-3 associated in vivo with TCR alpha enhancer, the activity of which is known to be required in regulating chromatin accessibility to the V(D)J recombinase. Thus, CSB may temporally regulate local chromatin structure and help to spread TCR alpha enhancer activity over the entire 70-kb Jalpha locus by forming developmentally regulated CSB-nucleoprotein complexes and by interacting with other cis-regulatory element-nucleoprotein complexes present within the TCR alpha / delta locus.

Discrete species of activated oxygen yield different cytochrome P450 heme adducts from aldehydes

Aldehydes are known to inactivate cytochrome P450 in the reconstituted enzyme system containing NADPH and NADPH-cytochrome P450 reductase under aerobic conditions in a mechanism-based reaction involving heme adduct formation [Raner, G. M., Chiang, E. W. , Vaz, A. D. N., and Coon, M. J. (1997) Biochemistry 36, 4895-4902]. In the study presented here, artificial oxidants were used to examine the mechanism of aldehyde activation by purified P450 2B4 in the absence of the usual O(2)-reducing system, and the adducts that were formed were isolated and characterized. With hydrogen peroxide as the oxidant, 3-phenylpropionaldehyde gives an adduct with a mass corresponding to that of native heme modified by a phenylethyl group, presumably arising from the reaction of a peroxy-iron species with the aldehyde to give a peroxyhemiacetal, which upon deformylation yields the alkyl radical. NMR analysis indicated that the substitution is specifically at the gamma-meso position. In contrast, with m-chloroperbenzoic acid as the oxidant, an adduct is formed from 3-phenylpropionaldehyde with a mass that is consistent with the addition of a phenylpropionyl group, apparently arising by hydrogen abstraction from the aldehyde to give the carbonyl carbon radical. m-Chloroperbenzoic acid by itself forms a heme adduct with a mass corresponding to the addition of a chlorobenzoyloxy group apparently derived from homolytic oxygen-oxygen bond cleavage. These and other results with nonanal and 2-trans-nonenal support the concept that this versatile enzyme utilizes discrete oxidizing species in heme adduct formation from aldehydes.

Epidural catheter placement in the rabbit--a novel approach

BACKGROUND

Using a pediatric epidural set and through caudal approach, we studied a relatively non-invasive technique for epidural percutaneous cannulation in rabbit for chronic laboratory investigations.

METHODS

Ten rabbits weighing over 3 kg were chosen and anesthetized with intravenous pentothal. A #19 pediatric Touhy needle and 23-gauge catheter were used for cannulation. Via the caudal approach, the epidural space could be located either by a "give" or with a technique of loss of resistance. Under fluoroscopy the catheter was tested with the injection of contrast medium for the confirmation of the proper position. The catheter was then tunneled under the skin and secured. The rabbits were kept in standard care for 4 weeks and then sacrificed by intraperitoneal pentothal overdose. A pathologist blinded to the study carefully examined the whole spine by laminectomy from cervical to coccyx and the findings were recorded.

RESULTS

With the injection of contrast medium, the final position of the catheter was validated by fluoroscopy in all rabbits. Two rabbits sustained immediate complications from the contrast medium and/or technique, of which one died shortly after the contrast medium injection and the other had weakness of the hind legs for a week. At sacrifice, all the catheters were found in good position. Two had hematoma associated with signs of trauma. One developed subcutaneous abscess. One had stitch infection of skin.

CONCLUSIONS

Percutaneous cannulation of epidural catheter is possible in the rabbit. Complications could be ameliorated by prudent approach in a skillful hand. It can be a reasonable model for the study of centrally administered medicines and their neurotoxicity.

Cytochrome P450 2E1 mRNA in the rat prostate: detection and quantitation by competitive reverse transcription and polymerase chain reaction

Cytochrome P450 2E1 plays a pivotal role in the metabolic activation of a wide variety of low molecular weight environmental toxicants and procarcinogens. In the present study, expression of the P450 2E1 gene in the rat prostate gland was quantitated by competitive reverse transcription and the polymerase chain reaction. To assess accurately the induction level of P450 2E1 mRNA in the prostate after pyridine treatment of rats, a recombinant standard RNA was generated that is homologous to the sequence of P450 2E1 mRNA except for an internal deletion of 100 bases. The data indicate that P450 2E1 mRNA is present in the prostate of untreated animals and is induced about four-fold by treatment with pyridine. The results suggest that exposure to certain environmental chemicals and procarcinogens may increase P450 2E1 levels in the prostate gland and thus could enhance formation of reactive, carcinogenic metabolites.

Calcium binding by human and rabbit serum paraoxonases. Structural stability and enzymatic activity

Equilibrium dialysis and Scatchard plots were used to establish that human and rabbit paraoxonases both have two calcium binding sites. Independent-site and stepwise constant analyses were used to calculate a higher affinity site (Kd1) of 3.6 +/- 0.9 x 10(-7) M for human A paraoxonase, and 1.4 +/- 0.5 x 10(-8) M for rabbit paraoxonase, and a lower affinity site (Kd2) of 6.6 +/- 1.2 x 10(-6) M for human A paraoxonase, and 5.3 +/- 0.94 x 10(-6) M for rabbit paraoxonase. In both species, the higher affinity sites were found to be essential to maintain hydrolytic activity; complete removal of calcium led to irreversible inactivation. The lower affinity sites were required for catalytic activity, and their binding of calcium was reversible. Experimentally estimated values of Kd2 based on the concentration of calcium required to obtain half the maximum enzymatic activity were 3 microM for human A and B paraoxonases, and also in the order of 3 microM for rabbit paraoxonase, using three different substrates. Calcium was the only metal found that protects against denaturation and also confers hydrolytic activity with these two mammalian paraoxonases.

The detection of cytochrome P450 2E1 and its catalytic activity in rat testis

Cytochrome P450 2E1 participates in the bioactivation of a wide variety of environmental and occupational pollutants. Such reactions may lead to the production of active carcinogenic metabolites. The presence of P450 2E1 in the testis and prostate has not yet been reported. In the present study, cytochrome P450 2E1 mRNA has been identified in the rat prostate and testis by reverse transcription PCR, southern blotting, and DNA sequencing. P450 2E1 protein from rat testis could be detected with immunoblot analysis, but was not detected in the prostate. The hydroxylation of p-nitrophenol, known to be mediated by P450 2E1, was demonstrated by HPLC measurement of product formation in microsomal fractions from the rat testis, but again not from prostate. Exposure of rats to pyridine resulted in a 2.9-fold increase of p-nitrophenol hydroxylation by testicular microsomes. Diethyldithiocarbamate, a selective mechanism-based inhibitor of P450 2E1, or a P450 2E1 monoclonal antibody, caused marked inhibition of testicular microsomal p-nitrophenol hydroxylase activity. These results indicate that cytochrome P450 2E1 is present in the rat testis, and that it is elevated by the treatment of the animals with pyridine. Thus, the presence and inducibility of cytochrome P450 2E1 in the testis may be of significance in the bioactivation of environmental chemicals to genotoxic metabolites.

A conserved sequence block in murine and human T cell receptor (TCR) Jalpha region is a composite element that enhances TCR alpha enhancer activity and binds multiple nuclear factors

A conserved sequence block (CSB) located in a noncoding region of the mouse and human TCR alpha/delta loci, showing six differences over 125 nucleotide positions (95% similar), was subjected to detailed analyses in this study. Transient transfection results showed that the CSB-containing element in conjunction with the TCR alpha enhancer up-regulated the alpha enhancer activity, whereas no enhancer activity was detected when CSB alone was assayed. In vitro occupancy analyses of CSB by nuclear factors reveal the existence of an unexpectedly intricate network of CSB-protein and protein-protein interactions. Lymphoid-specific as well as T-lineage-specific nuclear factors are involved to differentially form CSB-bound complexes in extracts of various tissues and cell lines. Liver was shown to contain factor(s) sequestering thymic CSB-binding factors. Furthermore, the putative binding sites for transcription factors known to be important for lymphoid-lineage development are present in CSB and are targeted by nuclear factors. On the basis of these results, we propose that the CSB element may play a role in shaping the chromatin structure by which the accessibility of TCR alpha/delta loci to the recombinase complex and/or to the transcriptional apparatus can be controlled.

Metabolic activation of trans-4-hydroxy-2-nonenal, a toxic product of membrane lipid peroxidation and inhibitor of P450 cytochromes

Lipid peroxidation in biological membranes is known to yield reactive aldehydes, of which trans-4-hydroxy-2-nonenal (HNE) is particularly cytotoxic. This laboratory previously reported that purified liver microsomal P450 cytochromes are directly inactivated to varying extents by HNE. We have now found a mechanism-based reaction in which P450s are inactivated by HNE in the presence of molecular oxygen, NADPH, and NADPH-cytochrome P450 reductase. The sensitivity of the various isozymes in the two pathways is different as follows: P450 2B4 and the orthologous 2B1 are inactivated to the greatest extent and 2C3, 1A2, 2E1, and 1A1 to a somewhat lesser extent by the pathway in which HNE undergoes metabolic activation. In contrast, 2B4 and 2B1 are insensitive to direct inactivation, and the reductase is unaffected by HNE by either route. Recent studies on the catalytic activities of the T302A mutant of P450 2B4 have shown that the rate of oxidation of a variety of xenobiotic aldehydes to carboxylic acids is decreased, but the rates of aldehyde deformylation and mechanism-based inactivation of the cytochrome are stimulated over those of the wild-type enzyme (Raner, G. M., Vaz, A. D. N., and Coon, M. J. (1997) Biochemistry 36, 4895-4902). Inactivation by those aldehydes apparently occurs by homolytic cleavage of a peroxyhemiacetal intermediate to yield formate and an alkyl radical that reacts with the heme. In sharp contrast, the rate of mechanism-based inactivation by HNE is decreased with the T302A mutant relative to that of the wild-type P450 2B4, and mass spectral analysis of the heme adduct formed shows that deformylation does not occur. We therefore propose that the metabolic activation of HNE involves formation of an acyl carbon radical that leads to the carboxylic acid or alternatively reacts with the heme.

A highly conserved apoptotic suppressor gene is located near the chicken T-cell receptor alpha chain constant region

A cosmid clone containing the chicken T-cell receptor alpha chain constant region (TCRAC) was sequenced. The cosmid contains the TCRAC gene, six putative joining gene segments (TCRAJ), and surprisingly, a chicken homologue for the human apoptotic suppressor gene, defender against cell death (DAD1). The DAD1 gene is 6.3 kilobases downstream of the TCRAC gene and has an inverted transcription orientation with respect to the TCRAC gene. The cDNA for the chicken DAD1 gene is 597 base pairs in length and encodes a highly conserved hydrophobic protein. The proximal location of DAD1 to the TCRAC locus has also been confirmed in both humans and mouse. The location of the DAD1 gene suggests that DAD1 may play an important role in T-cell related apoptotic activities.

Comparison of purified human and rabbit serum paraoxonases

Rabbit serum paraoxonase (PON) activity was reported to be nearly 20 times greater than that found for humans and all other mammalian species tested, to date. However, 85% of the amino acid residues are identical in human and rabbit PONs, and the two purified PONs show similar substrate specificity patterns. Both are stimulated by phospholipids and have two asparagine-linked sugar chains. Both also have one intramolecular disulfide bond and one free sulfhydryl residue per molecule. Both require Ca2+ for stability and for catalytic activity. Zn2+ and Cd2+ also stabilize both PONs and prevent irreversible denaturation, but neither metal confers catalytic activity. Maximum specific activities for both esterases were approximately 2,000 units of arylesterase activity/mg protein. In contrast, rabbit PON is more stable than human PON to heat inactivation and sodium dodecyl sulfate-polyacrylamide gel electrophoresis treatment. Chelex 100 strips Ca2+ from human PON more easily, and EDTA is less inhibitory with rabbit PON. We conclude that human and rabbit PONs have very similar active centers, but the latter binds Ca2+ more tightly, is a more stable enzyme, and is maintained at 3- to 4-fold higher steady-state concentrations in serum than its human counterpart. PON activity depends on adequate Ca2+ being available; therefore, apparently much higher levels of PON activity in rabbits can be explained by the reduced Ca2+ concentrations present in the early assay methods.