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R Weinshilboum

Publications and source records attributed to R Weinshilboum.

At least 37 records · Page 2Linked to original sources
PubMed1987

Human and rat liver phenol sulfotransferase: structure-activity relationships for phenolic substrates.

Phenol sulfotransferase (PST) catalyzes the sulfate conjugation of many phenolic drugs. Human liver contains thermostable (TS) and thermolabile forms of PST. Ion exchange chromatography shows that two isozymes of TS PST (peaks I and II) are present in human liver preparations. Rat liver contains four forms of PST that can be separated by ion exchange chromatography. Quantitative structure-activity relationship (QSAR) analysis was used to study phenolic substrates for both human and rat liver PST. Thirty-six substituted phenols were tested as substrates for partially purified human liver TS PST peak I. QSAR analysis resulted in derivation of the following equation: log 1/Km = 0.92 (+/- 0.18)log P - 1.48 (+/- 0.38)MR'4 - 0.64 (+/- 0.41)MR3 + 1.04 (+/- 0.63)MR2 + 0.67(+/- 0.44) sigma- + 4.03 (+/- 0.42). In this equation Km is the Michaelis constant, P is the octanol-water partition coefficient, MR is the molar refractivity of substituents at the 2-, 3-, and 4-positions, and sigma- is the Hammett constant. Values of log 1/Km calculated with this equation were highly correlated with log 1/Km values (r = 0.950) that were observed experimentally. Nine phenols were also tested as substrates for partially purified human liver TS PST peak II. Log 1/Km values for these compounds were significantly correlated for the two isozymes of TS PST (r = 0.992, p less than 0.001). QSAR analysis was also used to derive equations that described the behavior of phenolic substrates for rat liver PST forms I and II. These equations differed substantially from the equation derived for compounds tested with human liver TS PST peak I. Therefore, the characteristics of the active sites of human liver TS PST peak I and rat liver PST forms I and II appear to differ. Application of these equations may make it possible to predict Km values of phenolic substrates for human liver TS PST and for rat liver PST forms I and II.

Animals↗
PubMed1986

Analysis of the distribution of erythrocyte sodium lithium countertransport in a sample representative of the general population.

Numerous studies of sodium-lithium countertransport (Na-Li CNT) have reported higher rates in essential hypertensives versus normotensive controls. We studied the distribution and the mode of inheritance of Na-Li CNT using a sample of 238 unrelated individuals and a sample of 245 individuals in 50 pedigrees all sampled from the population at large. The distribution of Na-Li CNT is continuous and bimodal. Our results indicate that there is a large genetic contribution to the distribution of Na-Li CNT. The hypothesis that the effect that causes bimodality is transmitted from generation to generation is supported by the fit to these data of a restricted transmission model with tau 2 = 0.749. We hypothesize that this deviation of tau 2 from its Mendelian expectation may be attributable to heterogeneity in the etiology of the bimodality in the Na-Li CNT distribution in the population at large.

Adolescent↗
PubMed1984

Major gene model for the inheritance of catechol-O-methyltransferase activity in five large families.

Five large families including 1,189 individuals were each ascertained through one proband with essential hypertension. Four of the probands were white and one was black. Erythrocyte catechol-o-methyltransferase (COMT) activity was measured in 551 family members. Standard statistical methods were used to investigate sex, age, and family differences in COMT activity. Maximum-likelihood methods were used to fit mixtures of normal distributions to COMT activity. COMT activity is distinctly bimodal. Pedigree segregation analyses were performed on the untransformed COMT values, their square roots, and natural logarithms in each family. In no family and under none of the three transformations was it possible to reject the hypothesis of Mendelian transmission of a major gene with two alleles in Hardy-Weinberg equilibrium. In most cases a genetic hypothesis with complete dominance or recessiveness, or a hypothesis of equal transmission probabilities was rejected. While the different transformations had a large effect on the skewness and kurtosis of the overall distribution of the data, they had little effect on the outcome of these segregation analyses. Therefore, this study strongly supports the concept that variation in COMT activity is due in large part to the effects of a major gene.

Adult↗
PubMed1984

Linkage relationships between a major gene for catechol-o-methyltransferase activity and 25 polymorphic marker systems.

Segregation analysis has provided evidence suggesting the existence of a major gene for catechol-o-methyltransferase (COMT) activity in man. Five large families (4 Caucasian, 1 black), with a total of 1,189 individuals, were ascertained as part of a genetic study of blood pressure. Erythrocyte COMT activity and status at 25 polymorphic genetic marker loci were determined on more than 518 individuals in these pedigrees. Genetic linkage analysis of COMT with each of the 25 marker loci was performed in two ways: 1) using parameter estimates from segregation analysis of untransformed COMT activity, and 2) using parameter estimates from segregation analysis of the power transformation of the COMT activity that maximized the likelihood of the genetic hypothesis in each family. Tight and close linkage were excluded at 21 and 15 loci, respectively. A lod score of 1.27 at theta = 0.1 was found between the loci for COMT activity and phosphogluconate dehydrogenase (PGD). Transformation of the data had little effect on the outcome of the linkage analysis.

Catechol O-Methyltransferase↗
PubMed1983

Thermolabile and thermostable human platelet phenol sulfotransferase. Substrate specificity and physical separation.

Human platelets contain at least two forms of phenol sulfotransferase (PST), a thermolabile (TL) form for which dopamine is a substrate and a thermostable (TS) form for which micromolar concentrations of phenol can serve as substrate. At higher concentrations phenol is also a substrate for the TL form. Studies of the regulation and the possible clinical value of measurements of platelet PST have been hampered because there is no specific substrate for the TS form of the enzyme. The purposes of these experiments were to determine whether there might be a better substrate than phenol for use in measurement of the activity of the TS form of platelet PST, and to attempt to physically separate the two forms of the platelet enzyme. The results of substrate kinetic, thermal stability, and inhibitor studies performed with platelet homogenates were all compatible with the conclusion that p-nitrophenol and 6-OH-melatonin were substrates for both the TS and TL forms of platelet PST. Norepinephrine, epinephrine and 5-OH-tryptamine were substrates for only the TL form. The apparent Km constants of the two forms of PST for p-nitrophenol differed by 7,100-fold when measured in platelet homogenates. This difference was 200 times greater than that which has been reported for phenol. Therefore, p-nitrophenol is the preferred substrate for measurement of the TS PST activity if interference by the TL activity is to be avoided. This information made it possible to use p-nitrophenol as a substrate in experiments designed to separate the two forms of platelet PST.(ABSTRACT TRUNCATED AT 250 WORDS)

Arylsulfotransferase↗
PubMed1982

Platelet phenol sulfotransferase activity: correlation with sulfate conjugation of acetaminophen.

Human platelets contain two independently regulated forms of the drug conjugating enzyme, phenol sulfotransferase (PST). One form of platelet PST activity is relatively thermolabile (TL) and the other is relatively thermostable (TS). Acetaminophen is a substrate for both the TS and TL forms of PST. Our aim was to determine whether individual variations in platelet PST activity might reflect variations in teh sulfate conjugation of oral acetaminophen. Platelet PST activity was measured in blood samples from 29 randomly selected subjects. There was no significant correlation between the independently regulated activities of the TS and TL forms of PST in the platelets of these subjects (r = 0.16, P less than 0.4). Each of the 29 subjects ingested 10 mg/kg acetaminophen and 24-hr urinary excretions of acetaminophen, acetaminophen glucuronide, and acetaminophen sulfate were measured. Average 24-hr urinary excretions of acetaminophen, acetaminophen glucuronide, and acetaminophen sulfate were 2.3%, 46.9%, and 35.0% of the total dose of drug. There were significant correlations between the activities of both the TS and TL forms of platelet PST and the excretion of acetaminophen sulfate expressed as a percentage of the dose of the drug (r = 0.62, P less than 0.001; r = 0.456, P less than 0.02). The correlation coefficient between the TS activity and the excretion of acetaminophen sulfate was significant when the excretion of sulfate conjugate was expressed as a percentage of the sum of acetaminophen plus conjugated metabolites excreted (r = 0.565, P less than 0.002). Our data demonstrate that relative levels of platelet PST activity reflect individual variations in the urinary excretion of the sulfate conjugate of acetaminophen.

Acetaminophen↗
PubMed1982

alpha-Methyldopa, alpha-methyldopamine an alpha-methylnoradrenaline: substrates for the thermolabile form of human platelet phenol sulphotransferase.

1 Sulphate conjugation catalyzed by phenol sulphotransferase (PST) is an important pathway in the catabolism of alpha-methyldopa (MD). Variations in PST activity in an easily obtained tissue such as the human platelet might reflect individual differences in the sulphate conjugation of MD in other organs and tissues. There are at least two forms of human platelet PST, a thermolabile form for which dopamine is a substrate and a thermostable form for which low concentrations of phenol can serve as a substrate. 2 MD, alpha-methyldopamine (MDA) and alpha-methylnoradrenaline (MNA) were tested as substrates for human platelet PST. All three were substrates for the thermolabile form of the enzyme and none were substrates for the thermostable form of PST. Apparent Michaelis-Menten (Km) values for MD, MDA and MNA were 5.5, 0.014 and 0.28 mM, respectively. Apparent Km values for 3'-phosphoadenosine-5'-phosphosulphate, the sulphate donor for the reaction, were 0.08, 0.13 and 0.10 microM, respectively, for the three catechol substrates. The pH optima for the reaction were 7.5 for MD and 6.5 for both MDA and MNA. 3 When platelet homogenates from 20 individual subjects were tested, there were significant correlations between PST activities measured with dopamine and those measured with MD, MDA and MNA (r = 0.54, 0.98 and 0.93, P less than 0.02, less than 0.001, and less than 0.001, respectively), but not between activities measured with low concentrations of phenol and those measured with MD, MDA and MNA (r = 0.021, 0.045 and 0.046, respectively). There results were also compatible with the conclusion that MD, MDA and MNA were substrates for the thermolabile form of platelet PST. 4 These observations will make it possible to test the hypothesis that variations in the activity of the thermolabile form of platelet PST may reflect individual differences in the sulphate conjugation of MD, MDA and MNA.

Arylsulfotransferase↗
PubMed1982

Family studies of plasma dopamine-beta-hydroxylase thermal stability.

There are large individual variations in the thermal stability of human plasma dopamine-beta-hydroxylase (DBH). These variations are a characteristic of the DBH molecule itself. Individual subjects may be classified as those with thermolabile and those with thermostable plasma DBH. Of 362 randomly selected unrelated children, 8.01%, and of 238 randomly selected unrelated adult subjects, 5.46% had thermolabile plasma DBH. There was not a significant correlation of DBH thermolability with either sex or age on the basis of data from 230 adults and children in 53 randomly selected families. Subjects with thermolabile DBH had basal enzyme activity only about 55% of that in subjects with stable enzyme. There was not a direct relationship between DBH thermolability and the allele DBHL, the presence of which results in very low basal enzyme activity. There was a significant familial aggregation of the trait of DBH thermolability, but there was not a significant correlation of this trait among spouses. Although preliminary pedigree evaluation raised the possibility of monogenic inheritance of the trait of DBH thermolability by an autosomal recessive mechanism, three separate families in which both parents had thermolabile enzyme included offspring with thermostable DBH. All five of these offspring had very low basal plasma DBH and were presumed to be homozygous for the allele DBHL. These observations raised the possibility that the trait of plasma DBH thermolability may be inherited, and that there may be an interaction between the locus or loci responsible for thermal stability and the locus DBH.

Adolescent↗
PubMed1981

Thermal stability and the biochemical genetics of erythrocyte catechol-O-methyl-transferase and plasma dopamine-beta-hydroxylase.

The levels of activity of human erythrocyte (RBC) catechol-O-methyl-transferase (COMT) and human plasma dopamine-beta-hydroxylase (DBH) are inherited in a monogenic fashion. The COMT in erythrocytes of subjects homozygous for the allele for low basal enzyme activity, COMTL, is more thermolabile than that in the erythrocytes of subjects with genetically high basal enzyme activity. This observation suggests that the locus COMT may represent the structural gene for COMT in man. Wide individual variations in the thermal stability of human plasma DBH also occur. There is a significant familial aggregation of the trait of thermolabile plasma DBH. Although subjects with thermolabile plasma DBH have average basal plasma DBH activity only about 55% of that of subjects with thermostable enzyme, the trait of thermolability does not cosegregate with DBHL, the allele for very low basal plasma DBH activity. Studies of thermal stability may help to increase our understanding of the biochemical basis of the genetic regulation of catecholamine enzymes in man.

Catechol O-Methyltransferase↗
PubMed1977

Inheritance of low immunoreactive human plasma dopamine-beta-hydroxylase. Radioimmunoassay studies.

Inheritance plays an important role in the determination of human plasma dopamine-beta-hydroxylase (DBH) enzymatic activity. It has been demonstrated that an allele (d) for very low enzymatic plasma DBH is inherited as an autosomal recessive trait. A radioimmunoassay for human DBH was developed to test the hypothesis that the presence of this allele results in a decrease in plasma DBH protein levels. The mean immunoreactive DBH (IDBH) in blood from a randomly selected population of adolescents was 824+/-38 ng/ml (mean+/-SEM, n = 134). The correlation coefficient of enzymatic DBH with IDBH for this group of 134 adolescents was 0.84 (P < 0.001). Of these subjects, 3.7% had values of < 100 ng/ml and appeared to compose a separate subgroup analogous to the 3-4% of the population that is homozygous for the allele for low enzymatic activity. There was a significant sibling-sibling correlation of IDBH values in the 14 sibling pairs included among the 134 subjects studied (r = 0.60, P < 0.025). IDBH was also measured in blood from 56 subjects homozygous (dd) for the allele for low enzymatic DBH (enzymatic activity < 50 U/ml) and in blood of 80 first-degree relatives of homozygous probands. All but two dd subjects had IDBH levels of <100 ng/ml. Results of family studies were compatible with the autosomal recessive inheritance of an allele for IDBH levels of less than 100 ng/ml which segregates with the allele for very low enzymatic activity. Average IDBH in blood of 37 obligate heterozygotes as determined by family studies (Dd) was 599+/-53 ng/ml (mean +/- SEM), significantly lower than the IDBH values found in a randomly selected population (P < 0.005). These results are compatible with the conclusion that the presence of the allele for low plasma enzymatic DBH results in a decrease in the quantity of DBH protein in human plasma.

Adolescent↗
PubMed1977

Dissociation of changes in enzymatic and immunoreactive rat serum dopamine bets-hydroxylase during growth and development.

Dopamine beta-hydroxylase (DBH) activity was measured in the serum, heart and salivary glands of Sprague-Dawley rats from 1 day after birth to 90 days of age. Serum DBH activity in blood from newborn animals was 90 units, approximately 4.5 times higher than in blood from 60- to 90-day-old rats. The serum enzyme activity increased to 130 units at 15 days of age and then decreased rapidly to adult levels (20 units). This decrease was not due to changes in levels of circulating inhibitors or activators of the enzyme. Four different inbred strains of rats also demonstrated a striking decrease in serum DBH activity between 15 and 60 days of age. Cardiac DBH in Sprague-Dawley rats increased approximately 5-fold from birth to 15 days of age, but failed to decrease thereafter. Salivary gland DBH activity also increased with maturation and failed to decrease. Plasma concentrations of epinephrine and norepinephrine were no different in blood samples obtained from Sprague-Dawley rats 15 and 60 days of age. This finding makes it less likely that the decrease in serum DBH activity with maturation represents a decrease in the functional activity of sympathetic nerve terminals. Antibodies against DBH were used to measure immunoreactive DBH protein in serum from rats 15 and 60 days of age. These studies demonstrated a significantly higher enzymatic activity per unit of immunoreactive protein in blood from young rats than in blood from animals 60 days of age. The ratios of enzymatic activity to immunoreactive protein as measured by the quantity of antibody necessary to precipitate 50% of the endogenous serum DBH activity (AD50) were 21.18 +/- 1.04 and 3.83 +/- 0.40 (mean +/- S.E.M.) for blood from animals 15 and 60 days of age, respectively. Among the possible explanations for this observation are included a greater quantity of enzymatically inactive but immunoreactive DBH in blood of adult animals as compared with the blood of young rats, or the existence of a different form of serum DBH in blood of young animals.

Aging↗