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.

Rat adrenal dopamine-beta-hydroxylase: purification and immunologic characteristics

Dopamine-beta-hydroxylase (DBH) was purified from rat adrenal medulla by a series of steps including sedimentation of membranes, extraction with n-butanol, ammonium sulfate fractionation, gel chromatography and ion-exchange chromatography. Disk gel electrophoresis revealed two protein bands, both of which were active. Antiserum was prepared against homogeneously purified bovine adrenal and rat adrenal DBH; Ouchterlony immunodiffusion, enzyme neutralization and complement fixation tests demonstrated that the respective homologous antisera were monospecific and of high titer. Antiserum to bovine DBH was only 2- to 3-fold more potent than pre-immune serum in inhibition of rat DBH activity. Complement fixation tests demonstrate that antiserum to bovine DBH has a 25,000-fold lower immunoreactivity with rat DBH than with bovine DBH.

Human serum dopamine beta-hydroxylase: correlation of enzymatic activity with immunoreactive protein in genetically defined samples

An antibody against human adrenal dopamine beta-hydroxylase (DBH) was used to quantitate immunoreactive DBH protein in human serum by an immunoprecipitation technique. A significant correlation was found between DBH enzyme activity and immunoreactive DBH protein in randomly selected serum samples (r = 0.94; N = 38; p less than .001). Studies of sera from obligate heterozygotes and individuals homozygous for the allele responsible for very low serum DBH enzymatic activity were compatible with a genetically mediated decrease in the quantity of circulating DBH protein in these subjects.

Human serum dopamine-beta-hydroxylase: purification, molecular weight, presence of sugars and kinetic properties

1) Dopamine-beta-hydroxylase has been purified from human serum. Ammonium sulphate fractionation was used as the first step, the enzyme being precipated between 30 and 50 percent saturation. For the second step, the enzyme was adsorbed onto, and then eluted from a column of Concanavalin A covalently bound to Sepharose 4B. In the third step the enzyme was further purified by passage through two successive columns of Sephadex G-200. The final step, chromatography on DEAE-cellulose, gave a preparation of the enzyme with a specific activity of 36 mumoles of octopamine formed/30 min per mg of enzyme, representing a purification from the starting serum of 3,000 fold. 200 mug of enzyme could be obtained from 200 ml of serum. 2) The enzyme preparation was found to be pure or, at most, only slightly contaminated (depending on the starting serum) as judged by the criterion of polyacrylamide gel electrophoresis. 3) No cross-reaction could be observed between the human serum enzyme and rabbit antibody against bovine adrenal dopamine-beta-hydroxylase. 4) The molecular weight of the enzyme was found to be 250,000, i.e. less than the bovine adrenal enzyme. 5) Kinetic properties of the enzyme were studied. The mechanism of action of the enzyme was found to be similar to that of the bovine adrenal enzyme. Real kinetic parameters for both tyramine and ascorbate were calculated and found to be the same as those described for the bovine adrenal enzyme. 6) Interaction with Concanavalin A strongly suggests that the serum dopamine-beta-hydroxylase is a glycoprotein.

Bovine adrenal medullary chromogranin A: studies on the structure and further evidence for identity with dopamine-beta-hydroxylase subunit

1. Chromogranin A was purified by the use of polyacrylamide gel electrophoresis. The amino acid composition of chromogranin A appeared to be nearly identical to that reported by other investigators and, moreover, was confirmed to be similar to that of dopamine beta-hydroxylase. 2. Dansyl-end group analysis revealed the presence of leucine as the only amino-terminal residue and quantitative estimations showed the presence of two leucine residues per molecule of 77 000 molecular weight. 3. Tryptic and CNBr patterns were obtained. Data are in good agreement with the concept of two nearly identical polypeptide chains per chromogranin A molecule of mol. wt 77 000. Patterns were compared with those obtained in parallel dopamine beta-hydroxylase and support the idea that chromogranin A and the dopamine beta-hydroxylase subunit are identical. Digestion with leucine amino peptidase gave further additional evidence for this suggestion. 4. Chromogranin A appeared to be free of carbohydrates. No cross-reaction was detected between chromogranin A and rabbit antibody against bovine adrenal dopamine beta-hydroxylase.

Effects of reserpine on activities and amounts of tyrosine hydroxylase and dopamine-beta-hydroxylase in catecholamine neuronal systems in rat brain

Reserpine (10 mg/kp i.p.) increased the activities of the enzymes tyrosine hydroxylase (TH) and dopamine-beta-hydroxylase, but not dopa decarboxylase, 2- to 3-fold in the nucleus locus ceruleus of rat brain. The TH response was dose-dependent, reached a maximum by 48 hours and recovered by 3 weeks. The increased activities of TH and dopamine-beta-hydroylase were shown by immunotitration with specific antibodies to each enzyme to be due entirely to increased accumulation of specific enzyme protein. At a time when the reserpine-elicited accumulation of TH was increased 300% in the locus ceruleus, activity of the enzyme only increased 20% in hypothalamus and not at all in substantia nigra or caudate nucleus. Reserpine increased the accumulation of TH, primarily in the cell bodies and to a far less degree in the terminals of neurons of locus ceruleus but not in dopaminergic neurons of the nigrostriatal system. The time course of enzyme accumulation parallels that of depletion of monoamines in brain.

The anatomical characteristics of dopamine-beta-hydroxylase accumulation in ligated sciatic nerve

The anatomical characteristics of the accumulation of dopamine-β-hydroxylase (DBH) that occurs after ligation of rat sciatic nerve were examined in detail using a recently developed specific immunofluorescence method. Although rapid accumulation of DBH occurred showing the presence of axonal transport, the anatomical observations indicated that the build-up was considerably more complex than the simple "blockade" model frequently used as a basis for computation of transport rates from quantitative estimates of accumulation. During the early time period (7 hr) the situation was complicated by a substantial amount of accumulation of DBH distal to the ligation. By 24 hr after ligation the distal accumulation was small compared to that present proximally. The size of the discrete areas covered by DBH fluorescence at 24 hr indicated that axonal membranes may have already started to rupture, thus releasing vesicles into the extracellular space. By 48 hr after ligation the DBH was no longer confined to the area near the ligation, but extended 3.6 mm proximally. By 96 hr after ligation there had been a net loss of DBH fluorescence indicating that degradation and clearance of accumulated DBH had occurred.

Studies on the carbohydrate moiety of dopamine beta-hydroxylase: interaction of the enzyme with concanavalin A

Dopamine beta-hydroxylase [EC 1.14.17.1; 3,4-dihydroxyphenylethylamine, ascorbate:oxygen oxidoreductase (beta-hydroxylating)], a glycoprotein, was found to interact strongly with the plant lectin, concanavalin A. This interaction did not appear to alter the catalytic properties of the enzyme and did not prevent interaction of the protein with specific antibodies. Dopamine-beta-hydroxylase is adsorbed to concanavalin A covalently bound to Sepharose and can be eluted with alpha-methylmannoside. The enzyme is catalytically active when it is immobilized on a concanavalin A-Sepharose column. Enzymic removal of four of seven mannose residues present in the monomer does not result in the loss of any catalytic activity. It is concluded that the active site is not near the point of carbohydrate attachment on the molecule and that this may be of significance in orienting the enzyme on the vesicular membrane.