Biomedical subjects

C L Chen

Publications and source records attributed to C L Chen.

At least 199 records · Page 11Linked to original sources

PubMed1997

Determination of flunixin in equine urine and serum by capillary electrophoresis.

A capillary electrophoresis (CE) and a solid-phase extraction method was developed for the determination of flunixin in equine urine and serum. The suitable CE run conditions were described. The factors affecting flunixin recovery rates were investigated and optimum solid-phase extraction conditions for flunixin in equine urine and serum were established. Limits of detection and quantitation were 3.4 and 5.6 ng/ml for serum and 16.9 and 33.1 ng/ml for urine, respectively. The recoveries exceeded 96% for urine and 79% for serum. Urine samples from race horses and urine and serum samples from a mare administrated with flunixin were analyzed with this procedure.

Animals↗

PubMed1997

Higher frequency of glutathione S-transferase deletions in black children with acute lymphoblastic leukemia.

The genetic polymorphisms in human glutathione S-transferases (GST) M1 and T1 have been associated with race, disease risk, and outcome of some adult cancers. Also, there are racial differences in the incidence and characteristics of childhood acute lymphoblastic leukemia (ALL). Our objectives were to compare the frequency of the null genotype for GSTM1, GSTT1, or both in children with ALL to that in healthy controls, and to determine whether GST genotype was associated with treatment outcome and prognostic factors. We studied GSTM1 and GSTT1 genotypes in somatic cell DNA from black children and white children with ALL and in 416 healthy controls, using a polymerase chain reaction technique. Ninety of 163 (55.2%) white ALL patients and 14 of 34 (41.2%) black patients were GSTM1 null, frequencies not significantly different (P = .19) than healthy controls (53.5% in whites and 27.6% in blacks), although there was a trend toward more null genotypes in black ALL patients. Twenty-three of 163 (14.1%) white ALL patients and 12 of 34 (35.3%) black ALL patients were GSTT1 null, not different (P = .34) than the frequencies in healthy controls (15.0% in whites and 24.1% in blacks). However, the frequency of the "double-null" genotype, lacking both GSTM1 and GSTT1, was higher in black patients with ALL (8 of 34 or 23.5%) than in black controls (3.9%) (P = .0005), but this was not the case in white patients with ALL (10 of 163 or 6.1%) compared to white controls (8.0%) (P = .68). In stratified analyses, the GST double-null genotype was not associated with other characteristics that might differ between whites and blacks with ALL, such as age, T-lineage immunophenotype, presenting white blood cell count, DNA index, or insurance status. The null genotype for GSTM1, GSTT1, or both was not found to be a prognostic factor for disease-free survival or probability of hematologic remission; central nervous system relapse tended to be less common in those with the GSTM1 null genotype (P = .054). The double-null genotype for GSTM1 and GSTT1 is more common among blacks but not whites with childhood ALL. These data suggest that GST genotype, coupled with unidentified additional risk factors, may play a role in risk of childhood ALL in American blacks.

Adult↗

PubMed1997

Neuroglian is expressed on cells destined to form the prothoracic glands of Manduca embryos as they segregate from surrounding cells and rearrange during morphogenesis.

A cell surface protein (3B11) is differentially expressed in the embryonic labial segment of Manduca as two circular monolayers of epithelial cells invaginate and segregate from surrounding epithelial cells. The cells that invaginate and preferentially express 3B11 represent the presumptive prothoracic glands. These cells continue to express protein 3B11 as they rearrange to form first a three-dimensional aggregate and later anastomosing filaments of cells. In the differentiated prothoracic gland, expression of 3B11 is restricted to sites of cell-cell contact. Cloning and sequencing of the cDNA for protein 3B11 revealed that this protein is the Manduca counterpart of Drosophila neuroglian and mouse L1. These surface proteins are known to function as adhesion/recognition molecules during development. Manduca neuroglian shares 58 and 31% identity respectively with the Drosophila and mouse proteins and has a cytoplasmic domain of over 100 amino acids.

Amino Acid Sequence↗

PubMed1997

Variations of the middle and inferior right hepatic vein: application in hepatectomy.

We evaluated the anatomic variations of the middle right hepatic vein (MRHV) and inferior right hepatic vein (IRHV) and their clinical application to the possibility of right subtotal hepatectomy. In 400 of normal livers studied with ultrasound, the IRHV was found to drain segment 6 of the liver and flow into the inferior vena cava (IVC) in 72 (18%) cases. In 22 (5.5%) cases, the MRHV was found to drain segment 5 of the liver and flow into the IVC. The size of the IRHV ranged from 0.1 cm to 0.8 cm with an average of 0.46 cm. For the MRHV, the sizes ranged from 0.1 cm to 0.9 cm with an average of 0.34 cm. In 10/79 (12.6%) cases the IRHV and in 4/ 22 (18.1%) cases the MRHV were bigger than the right hepatic vein (RHV). The distance between the RHV and IRHV ranged from 3 cm to 5 cm with an average of 3.7 cm. The distance between the RHV and MRHV ranged from 3 cm to 3.3 cm with an average of 3.1 cm. A hyperechoic edge, similar to that of the portal vein, was observed at the wall of the hypertrophic IRHV and was 0.3 cm or larger in size. Preoperative delineation of this complex venous anatomy is very important. It provides vital information in the preoperative evaluation needed before performing a right subtotal hepatectomy with preservation of segment 6 or segment 5 of the liver, and with RHV resection. Prior to undertaking a right hepatectomy, clamping the hypertrophic MRHV and IRHV electively may minimize intra-operative blood loss and extrahepatic spread of the malignancy.

Adolescent↗

PubMed1997

CCAAT/enhancer-binding protein beta is not affected by tetrachlorodibenzo-p-dioxin (TCDD) inhibition of 3T3-L1 preadipocyte differentiation.

The differentiation of 3T3-L1 preadipocytes is induced by the coordinate activation of trans-acting factors in response to inducers. Depending on the time of treatment, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) was effective in inhibiting 3T3-L1 preadipocyte differentiation and the expression of differentiation-dependent trans-acting factors. Based on glycerol-3-phosphate dehydrogenase activity, in the differentiation of 3T3-L1 cells was decreased by 70% in cells treated with TCDD before the induction of differentiation, 25% during induction, and not at all after induction. This time-dependent inhibition of cell differentiation by TCDD was correlated with the levels of aryl hydrocarbon receptor (AhR). TCDD treatment decreased the mRNA levels of C/EBP alpha and PPAR gamma 2 but did not affect the mRNA levels of RXR alpha and RAR alpha. Furthermore, TCDD did not change the mRNA or protein levels of C/EBP beta, which is thought to play a role in inducing C/EBP alpha and PPAR gamma 2 expression. These results suggest that TCDD inhibited 3T3-L1 preadipocyte differentiation through the AhR pathway, and the change of C/EBP beta mRNA and protein was not involved in reducing mRNA expression of C/EBP alpha and PPAR gamma 2.

3T3 Cells↗

PubMed1997

Lipoblastomatosis in a newborn: case report.

A male newborn had a well-circumscribed, solid mass on the right anterior chest wall at birth. Computed tomography disclosed an infiltrating soft-tissue mass over the right 6th to 9th ribs near the costochondral junction. Surgical excision was done at the age of 5 days. Pathologic examination showed lipoblastomatosis.

Humans↗

PubMed1997

Leisure-time physical activity in relation to breast cancer among young women (Washington, United States).

It has been hypothesized that women who participate in vigorous physical activity may have lower risk of breast cancer due to lower lifetime exposure to ovarian hormones. A population-based case-control study was conducted to investigate the association between leisure-time physical activity and risk of breast cancer among women aged 21 to 45 years. Cases were 747 women diagnosed with invasive breast cancer between 1983 and 1990 in three counties of western Washington state (United States), and were identified through the Seattle-Puget Sound Surveillance, Epidemiology, and End Results (SEER) registry. Controls were 961 women selected from the same area by random-digit telephone dialing. Physical activity was assessed through personal interview, with questions on frequency and duration of each type of recreational activity during the two-year period immediately prior to reference data (date of diagnosis for cases and a comparable assigned date for controls) and between ages 12 and 21. For the two-year time period before diagnosis, there was no association with frequency of activity (age-adjusted odds ratio [OR] = 0.93, 95 percent confidence interval [CI] = 0.71-1.22 for four or more episodes per week cf none), total hours spent in physical activity (age-adjusted OR = 0.92, CI = 0.71-1.22 for four or more hours per week cf none) or MET (metabolic equivalent energy expenditure unit) (age-adjusted OR = 0.95, CI = 0.73-1.23 for 18 or more METs per week of none), nor any trend is risk with increasing activity levels. Similarly, there was no association between leisure activity during adolescence and breast cancer risk. These results were not confounded further by body mass index (wt/ht2), age at menarche, age at first full-term pregnancy, parity, family history of breast cancer, or other measured health behaviors. Our findings do not support a protective effect of leisure-time physical activity either in the adolescent years or in adulthood on breast cancer in young women.

Adult↗

PubMed1997

Primary papular xanthoma of children: a clinicopathologic, immunohistopathologic and ultrastructural study.

Papular xanthoma (PX) is a very rare skin disorder. We describe a typical case of PX in a 13-month-old Chinese boy who presented with numerous yellow-red papulonodules, 2-8 mm in diameter, mainly on the face, both upper extremities, and abdomen of 10 months duration. Histologic studies showed a diffuse monomorphous infiltrate of foamy cells in the upper dermis. The foamy cells stained positively with oil red O and CD68. The periodic acid Schiff (PAS) stain, S-100 protein, CD1a, CD56, lysozyme, alpha1-antitrypsin, and factor XIIIa were all negative in the foamy cells. The electron microscopic (EM) studies revealed the morphologic features of macrophages with electron-dense, membrane-limited lipid vacuoles in the cytoplasm. After 14 months, neither spontaneous regression nor anetoderma-like scars were noted. Our immunohistochemical and ultrastructural studies support the notion that the origin of the foamy cells is the macrophage rather than the factor XIIIa (+) dermal dendrocyte. There was no associated or underlying disease in this case. We suggest the term primary PX for cases such as this one.

Foam Cells↗

PubMed1997

Living related donor liver transplantation.

Living related liver transplantation (LRLT) has been developed in response to the paediatric organ donor shortage. According to the International Living Donor Registry, 521 transplants had been performed in 515 patients between December 8 1988 and January 19 1996 in 30 centres worldwide. The overall actuarial patient and graft survival rates were 82.7 and 80%, respectively. Between June 17 1994 and November 30 1996, the authors performed 11 LRLT at the Chung Gung Memorial Hospital. The living donors consisted of 10 mothers and one father. The mean graft weight was 303 g and the mean graft recipient weight ratio was 2.2%. Donor hepatectomy was performed without vascular inflow occlusion. The intra-operative blood loss ranged from 30 mL to 120 mL with an average of 61 mL, and blood transfusion was not required in all donors both intra-operatively and during the postoperative period. Underlying diseases of the recipients were biliary atresia (n = 10) and glycogen storage disease (n = 1). The mean graft cold ischaemia time was 106 min, the mean second warm ischaemia time was 51 min and the mean interval between portal and arterial reperfusion was 81 min. The initial LRLT results were promising with all donors having been discharged without complication. The recipients experienced a few complications, all of which were manageable with early intervention. All 11 recipients are alive and well. These are encouraging results and the authors hope to expand the use of live donors for liver transplantation to cope with demand.

Adolescent↗

PubMed1997

Cytochrome P450 2D6 and glutathione S-transferase genotype in sudden infant death syndrome.

OBJECTIVES: The risk of sudden infant death syndrome (SIDS) has been linked with xenobiotic exposures, race and inheritance. Because cytochrome P450 2D6 (CYP2D6) and glutathione S-transferases (GSTM1 and GSTT1) are genetically regulated, polymorphically distributed, and responsible for detoxification of many centrally acting exogenous and endogenous bioactive compounds, our objective was to determine whether the prevalences of deficiencies in CYP2D6, GSTM1, and GSTT1 differ in SIDS victims compared to healthy controls. METHODS: CYP2D6 mutations (deletion, A, B, and T alleles) and GSTM1 and GSTT1 null genotypes were assessed in DNA from 50 SIDS victims. CYP2D6 phenotype, assigned using dextromethorphan urinary ratios, was assessed in 25 unrelated parents of SIDS victims. RESULTS: The CYP2D6B mutation was the only mutant CYP2D6 allele found in SIDS victims, present in 26.2% of patients (11/42) and 13.1% (11/84) of alleles. Adjusting for race, the prevalence of wild-type CYP2D6 alleles and of homozygous wild-type CYP2D6 phenotype was not different in SIDS victims compared to controls (P = 0.585 and 0.224, respectively). Among the 25 parents of SIDS victims, all subjects were extensive metabolizers, a prevalence not different from controls (P = 0.243). The prevalence of the null genotype for GSTM1, GSTT1 and double-null for GSTM1 and GSTT1 was 33.3%, 21.4% and 9.5%, respectively, among SIDS victims, and was not different than controls (P = 0.61, 0.1, 0.28, respectively). The combination of CYP2D6 homozygous wild-type genotype and the null genotype for GSTM1, GSTT1, or both GSTM1 + GSTT1 also did not differ in SIDS victims and controls. CONCLUSIONS: The frequencies of CYP2D6 mutant genotypes and the null genotypes for GSTM1 and GSTT1 were not different among SIDS victims compared to normal controls, and thus these polymorphisms are unlikely to identify families with a high risk of SIDS.

Cytochrome P-450 CYP2D6↗

PubMed1997

Differential threshold of length and response criterion for inspecting irregular objects.

This research investigated human visual sensitivity and bias in inspecting irregular objects. A preliminary study was conducted using the method of constants to determine the threshold value for judgment of size. A factorial experiment was conducted using payoffs, rate of defective items, and detectability in the signal-detection theory as the factors. In total, eight experimental conditions were tested. 10 college students were recruited as subjects. Each subject was asked to compare 40 teapot shapes to a standard teapot shape under eight experimental conditions. Defective shapes were generated by lengthening the vertical dimension of a standard teapot shape by a factor of 1.01 and 1.04 for 'low' and 'high' detectability. The decision time and responses of 'identical' or 'different' were collected under all experimental conditions. Analysis indicates that the decision-making strategy used to inspect this irregular object was very close to maximizing the accuracy of decision-making by considering the rate of defective items. This result is different from most research findings in signal-detection theory in which responses of human beings are similar to degraded Bayes optimizers. The standard deviation of the signal distribution was about 1.30 and 1.41 times that of the noise distributions for 'low' and 'high' detectability.

Decision Making↗

PubMed1997

Magnetic resonance venography in potential pediatric liver transplant recipients.

Vascular anomalies may be hazardous to liver transplantation, and pre-operative vascular evaluation is important for a safe and successful operation. The purpose of this study was to assess the utility and accuracy of time-of-flight (TOF) magnetic resonance venography (MRV) with three-dimensional (3D) reconstruction as an alternative for conventional catheter angiography in evaluating the portal venous system and inferior vena cava (IVC) in potential pediatric liver transplant recipients. Twenty consecutive cases of small children with biliary atresia were evaluated with TOF MRV with 3D reconstruction by Advantage Window workstation. All 20 cases underwent conventional angiography; two cases received transhepatic portography and three cases received splenoportographic study. The whole MRV examination and filming required less than 30 min. Findings of portal vein and IVC completely agreed with or were superior to the successful catheter angiographic images. The portal vein was occluded in five cases, and patent in fifteen cases which included: twelve hepatopetal flow, two hepatofugal flow and one small caliber portal vein. Varices were found in 18 cases. In the case of the IVC, 18 of them were normal and 2 had congenital abnormalities which included paired vena cava and hypoplasia vena cava with compensatory enlargement of the azygos and hemiazygos systems. Eight of the cases received liver transplantation, and the MRV findings totally correlated with the final anatomy as found intraoperatively. MRV is accurate for evaluating the condition of the portal venous system and IVC, detection, and determining the distribution and extents of the varices. It is a reliable, noninvasive and rapid technique which can be considered as an alternative workup for the invasive angiography and or portography in small children for pre-transplantation evaluation.

Angiography, Digital Subtraction↗

PubMed1997

Three-dimensional helical computed tomographic cholangiography: application to living related hepatic transplantation.

Variations in the anatomy of intrahepatic bile ducts complicate operations in living related hepatic transplantation (LRHT). Preoperative delineation of the biliary system is important to achieve successful results. The purpose of this study was to assess the utility and accuracy of three-dimensional helical computed tomographic cholangiography (3DHCTC) as a replacement for endoscopic retrograde cholangiography (ERC) in evaluating the anatomy of the intersegmental biliary connection of the potential donors in LRHT. Helical CT was performed in 16 potential donors after a slow infusion of 100 cm3 meglumine iodipamide. By using the maximum intensity projection and shaded surface displaced image reconstruction technique, three-dimensional images of the bile ducts were isolated from the surrounding hepatic parenchyma. Among the 16 potential donors, 3 cases underwent an ERC study and another 7 cases donated liver graft during LRHT. In all 16 cases the anatomy of the bilateral essential intrahepatic ducts was well displayed with and without the liver parenchyma background in an axial and three-dimensional fashion which had good correlation with images from ERC and intra-operative cholangiography. Two variants were found, including drainage of the right posterior intrahepatic duct into the left hepatic duct and direct drainage of the segment II bile duct into the common hepatic duct, respectively. It is concluded that unusual routes of intrahepatic ducts may necessitate a change in the cutting plane during graft retrieval and patterns of ductoenteral anastomosis to avoid potential complications to both donors and recipients. With the advantages of non-invasiveness and comparable accuracy in demonstrating biliary anatomy, 3DHCTC may replace the traditional ERC in the pre-transplant survey of potential donors for LRHT.

Adult↗

PubMed1997

Variations of the intrahepatic bile ducts: application in living related liver transplantation and splitting liver transplantation.

The variations in the anatomy of intrahepatic bile ducts complicate operations in living related liver transplantation (LRLT) and therefore preoperative delineation of the biliary system is important to achieve a successful outcome. The aim of this study was to establish a standard relationship between the biliary variations and the methods of the graft splitting and anastomosis. Of 958 endoscopic retrograde cholangiographies with good visualization of bile duct branches were selected and were available for evaluation of their ramifications and variants. According to drainage of right hepatic duct and left hepatic duct, we classified the bile ducts into two major groups. Unusual routes of the intrahepatic ducts were present in 105 cases (11% in group A) the right sectoral duct drained into the left hepatic duct directly; in 200 cases (21% in groups B) the duct of segment IV drained into right side or common hepatic duct; and in 29 cases (3% in groups B) the duct of segment: II and III drained into the CBD and right hepatic duct separately. There is no specific bile duct variation that forbids someone from LRLT and SLT, but unusual intrahepatic ducts routes may require a change both in the cutting plane during graft retrieval and pattern of ductoenteral anastomosis to avoid potential complications to both donors and recipients. Cholangiography for screening intrahepatic duct variations is therefore important for safe bile drainage for both donors and recipients.

Adolescent↗

PubMed1997

Inducible nitric oxide synthase expression in coronary arteries of transplanted human hearts with accelerated graft arteriosclerosis.

Inducible nitric oxide synthase (iNOS) is a high-output isoform of NOS that produces nitric oxide (NO), a nonspecific immune effector molecule. In some animal models of autoimmunity, the induction of iNOS has been shown to lead to inflammation and tissue damage, and it has been suggested that iNOS is an immune mediator in humans as well. Using in situ hybridization and immunohistochemical techniques, we demonstrate that iNOS mRNA and protein are present in the coronary arteries of transplanted human hearts with accelerated graft arteriosclerosis (AGA). iNOS is expressed in cells morphologically consistent with macrophages in the neointima of 7 of 10 of the transplanted vessels with AGA that were examined. In serial sections, these same cells express the macrophage marker CD68. In contrast, iNOS is absent from five native coronary arteries with atherosclerosis and absent from two normal coronary arteries. Although iNOS is expressed in macrophages in AGA, its role in the pathogenesis of AGA is unknown.

Adolescent↗

PubMed1997

Treatment of intrabony defects by polylactic acid matrix barrier--a one-year follow-up study.

The present investigation was conducted to evaluate the effect of a polylactic acid-citric acid softened membrane barrier during guided tissue regeneration (GTR) surgery on human intrabony defects. Eighteen patients were treated in the study and 16 patients completed the 1-year follow-up. In all, 27 intrabony defects were treated and clinical soft tissue measurements, including probing depth (PD), probing attachment level (PAL), and recession, were recorded. Results of the investigation demonstrated a significant reduction in PD (3.7 mm), a significant gain in PAL (4.2 mm), and a slight increase in recession (1.2 mm).

Adult↗

PubMed1996

Relationship between cytotoxicity and site-specific DNA recombination after in vitro exposure of leukemia cells to etoposide.

BACKGROUND: Etoposide, an inhibitor of the normal religation activity of the nuclear enzyme topoisomerase II, can induce a secondary acute myeloid leukemia characterized by site-specific DNA rearrangements. The schedule of drug administration appears to be a clinical risk factor for this devastating treatment complication. PURPOSE: We tested the hypothesis that prolonged exposure of leukemia cells in vitro to low concentrations of etoposide, compared with short exposures to high concentrations, could produce equivalent or greater desired cytotoxic effects, with decreased occurrence of undesired site-specific double-stranded DNA recombinational events (i.e., recombinogenesis). METHODS: We used the frequency of V(D)J (variable-diversity-joining) recombinase-mediated deletions of exons 2 and 3 of the hypoxanthine phosphoribosyltransferase (HPRT) gene as a biomarker of etoposide-induced, nonhomologous, site-specific DNA rearrangement. A polymerase chain reaction-based technique was used to measure exon 2 + 3 deletions in human lymphoid leukemia CCRF-CEM cells 6 days after either 4-hour or 24-hour treatment with etoposide at clinically relevant concentrations. Cytotoxic effects of etoposide (determined by the number of viable cells present in the treated compared with the control [i.e., untreated] cells) were measured 6 days after treatment of the cells. The frequency of the exon 2 + 3 deletion following the two treatment-duration conditions was compared by use of the Mantel-Haenszel statistic. All P values resulted from two-sided tests. RESULTS: Cytotoxicity increased with increasing etoposide concentration and exposure duration, as expected. By day 6, the frequency of exon 2 + 3 deletions was significantly higher (global P value = .0003) after the 4-hour treatment than after the 24-hour treatment, regardless of whether the frequency was assessed at etoposide concentrations achieving equivalent (e.g., 95%) cytotoxicity (14.2 x 10(-7) versus 4.1 x 10(-7) or at equivalent etoposide concentrations (e.g., 1 microM) (10.8 x 10(-7) versus 1.3 x 10(-7). Thus, the ratio of desired cytotoxic to undesired recombinogenic effects was higher with the 24-hour schedule. After the treated cells were subcloned at limiting dilutions, the frequency of the exon 2 + 3 deletion increased from 16.3 x 10(-7) to 4.33 x 10(-3), indicating that the recombinational event is not necessarily lethal. CONCLUSION: For all drug concentrations and levels of cytotoxicity studied in CCRF-CEM cells, there was a greater ratio of cytotoxicity to genetic recombination following prolonged exposure to etoposide than following brief exposure. IMPLICATION: These data suggest that recombinogenesis is not inextricably linked to cytotoxicity. If confirmed in the clinical setting, the use of prolonged dosage schedules may provide a means to decrease the risk of etoposide-induced acute myeloid leukemia without compromising treatment efficacy.

Acute Disease↗

PubMed1996

Positive charge at position 549 is essential for phosphatidylinositol 4,5-bisphosphate-hydrolyzing but not phosphatidylinositol-hydrolyzing activities of human phospholipase C delta1.

Point mutagenesis, phosphatidylinositol (PI), and phosphatidylinositol 4,5-bisphosphate (PIP2) hydrolysis assays and equilibrium centrifugation PIP2 assays were used to study the functional roles of four highly conserved arginine residues in the Y region of human phospholipase C delta1 (PLCdelta1) (Arg-527, -549, -556, -701). Most of the mutant enzymes were either partially defective or fully active in their abilities to catalyze the hydrolysis of PI or PIP2. However, upon substitution of Arg-549 by glycine or histidine, the mutant enzyme was defective in its ability to catalyze the hydrolysis of PIP2, but it is still able to hydrolyze PI. Replacing Arg-549 with lysine had little effect on the level of PI and PIP2 hydrolytic activities of the mutant enzyme. The residual PIP2 hydrolyzing activity of R549H is highly dependent on pH. R549H showed 5-10% of the PIP2-hydrolyzing activity of the native enzyme between pH 5 and 7 and nondetectable PIP2-hydrolyzing activity at pH 8. The PIP2-hydrolyzing activity of R549G was not detectable at all pH values. Kinetic analysis of PLCdelta1-catalyzed PIP2 hydrolysis revealed that the micellar dissociation constant Ks and interfacial Michaelis constant Km were similar in the native, R549K, and R549H enzymes; but the specific activity at the saturated substrate mole fraction and infinite level of substrate (Vmax) of the R549H mutant were reduced by a factor of 15. PIP2 competitively inhibits the native enzyme to hydrolyze PI at both pH 7 and 8. However, PIP2 inhibits R549H only at pH 7.0 and does not inhibit R549G at either pH. Taken together, these results suggest that positive charge at position 549 of PLCdelta1 protein is essential for the enzyme to recognize and catalyze the hydrolysis of PIP2 but not PI.

Calcium↗