Obesity, metabolism, and hypertension

The relationship between obesity and hypertension is complex and poorly understood. A developing body of information suggests that metabolic factors related to the obese state are importantly involved. The pertinent observations include: (1) Diet influences sympathetic nervous system activity. Fasting suppresses, while carbohydrate and fat feeding stimulate, sympathetic activity. (2) Dietary-induced changes in sympathetic activity contribute to the changes in metabolic rate that accompany changes in dietary intake. (3) Insulin-mediated glucose metabolism in the hypothalamus provides a link between dietary intake and sympathetic nervous system activity. And (4) hyperinsulinemia, a consequence of insulin resistance in the obese, is associated with hypertension. These observations have suggested the following hypothesis. Hyperinsulinemia results in sympathetic stimulation which drives thermogenic mechanisms, thereby increasing metabolic rate. The net result is a restoration of energy balance at the expense of hyperinsulinemia and increased sympathetic activity. Hypertension is thus the unfortunate consequence of hyperinsulinemia, which increases renal sodium reabsorption, and sympathetic stimulation of the heart, kidney, and vasculature. The data on which this hypothesis is constructed are reviewed and the implications discussed.     

Hepatic lipase and dyslipidemia: interactions among genetic variants,obesity, gender,and diet

Hepatic lipase (HL) plays a central role in LDL and HDL remodeling. High HL activity is associated with small, dense LDL particles and with reduced HDL2 cholesterol levels. HL activity is determined by an HL gene promoter polymorphism, by gender (lower in premenopausal women), and by visceral obesity with insulin resistance. The activity is affected by dietary fat intake and selected medications. There is evidence for an interaction of the HL promoter polymorphism with visceral obesity, dietary fat intake, and with lipid-lowering medications in determining the level of HL activity.The dyslipidemia with high HL activity is a potentially proatherogenic lipoprotein profile in the metabolic syndrome, in Type 2 diabetes, and in familial combined hyperlipidemia.     

Cloning, expression, purification, and characterization of biosynthetic threonine deaminase from Escherichia coli

Feedback inhibition of the regulatory enzyme threonine deaminase by isoleucine provides an important level of enzymic control over branched chain amino acid biosynthesis in Escherichia coli. Cloning ilvA, the structural gene for threonine deaminase, under control of the trc promoter results in expression of active enzyme upon induction by isopropyl 1-thio-beta-D-galactoside to levels of approximately 20% of the soluble protein in cell extracts. High level expression of threonine deaminase has facilitated the development of a rapid and efficient protocol for the purification of gram quantities of enzyme with a specific activity 3-fold greater than previous preparations. The catalytic activity of threonine deaminase is absolutely dependent on the presence of pyridoxal phosphate, and the tetrameric molecule is isolated containing 1 mol of cofactor/56,000-Da chain. Wild-type threonine deaminase demonstrates a sigmoidal dependence of initial velocity on threonine concentration in the absence of isoleucine, consistent with a substrate-promoted conversion of the enzyme from a low activity to a high activity conformation. The enzymic dehydration of threonine to alpha-ketobutyrate measured by steady-state kinetics, performed at 20 degrees C in 0.05 M potassium phosphate, pH 7.5, is described by a Hill coefficient, nH, of 2.3 and a K0.5 of 8.0 mM. The negative allosteric effector L-isoleucine strongly inhibits the enzyme, yielding a value for nH of 3.9 and K0.5 of 74 mM whereas enzyme activity is greatly increased by L-valine, which yields nearly hyperbolic kinetics characterized by a value for nH of 1.0 and a K0.5 of 5.7 mM. Thus, these effectors promote dramatic and opposing effects on the transition from the low activity to the high activity conformation of the tetrameric enzyme.     

Factors other than Light Affecting the Pineal Gland: Hypophysectomy, Testosterone, Dihydrotestosterone, Estradiol, Cryptorchidism, and Stress

This article reviews those factors other than light that affectthe activity of the pineal gland. Both testosterone and dihydrotestosteronewere shown to have tissue specific inhibitory effects on pinealMAO activity concomitant with an increased activity of the gland.Estradiol stimulated pineal MAO activity and decreased the activityof this gland. This effect also was tissue-specific. Bilateraland unilateral experimental cryptorchidism also decreased pinealMAO activity 3 to 4 weeks after surgery. Acute stresses appearto increase adrenal catecholamine output (epinephrine and norepinephrine)as well as to stimulate local adrenergic pathways, while chronicstress, such as starvation, appears to act through the adrenalcorticosteroids by decreasing pineal MAO activity thereby indirectlyincreasing melatonin synthesis. Thusly, both components of theadrenal gland appear to act in concert to increase effectivelymelatonin synthesis by the pineal gland. Irradiation and histaminehave also been reported to affect pineal function—thelatter specifically inhibits HIOMT activity. These observationsindicate that many factors other than light affect pineal morphologyand melatonin synthesis. The pineal appears to be a true neuroendocrineorgan that is affected by hypophysectomy and is responsive tofeedback and control from other organs within the mammalianorganism.     

Isolation,partial purification,characterization, and tissue distribution of phenylmethylsulfonyl fluoride-inhibited feline carboxypeptidase

Phenylmethylsulfonyl fluoride (PMSF)-inhibited carboxypeptidase from cat liver was purified 148-fold by chromatography on CM- and DEAE-cellulose with 27.3% yield. Molecular weight of the enzyme is 100-110 kD as determined by gel filtration on Sephadex G-150. The enzyme has maximum activity at pH 5.50-5.75; its activity is completely inhibited by PMSF or p-chloromercuribenzoate and partially inhibited by iodoacetamide. EDTA, 2-mercaptoethanol, N-ethylmaleimide, Co²⁺ and Ca²⁺, basic carboxypeptidase inhibitor guanidinoethylmercaptosuccinic acid, and angiotensin-converting enzyme inhibitor captopril do not influence its activity. The enzyme cleaves arginine from enkephalin-Leu5-Arg6 and dansyl-Phe-Leu-Arg to form enkephalin-Leu5 and dansyl-Phe-Leu, respectively, and very slowly cleaves leucine from carbobenzoxy-Gly-Leu. Further cleavage of either enkephalin-Leu5 or dansyl-Phe-Leu was not detected. The highest activity of this enzyme was found in adrenal glands and testicles; this activity was 30% lower in hypophysis, and still lower in liver and kidney. The PMSF-inhibited carboxypeptidase activity in brain was about 6-16 times lower than that in adrenal gland. In brain regions, the highest activity was detected in gray matter of cerebral hemispheres and cerebellum, and slightly lower activity was found in thalamus/hypothalamus, striatum, and hippocampus. The lowest activity was found in quadrigeminal bodies, medulla oblongata, and white matter of cerebral hemispheres. The enzyme exists mainly in soluble form; the activity of membrane-associated enzyme is 7-25% of soluble enzyme activity depending on tissue type. We consider here a possible involvement of PMSF-inhibited carboxypeptidase in the metabolism of biologically active peptides.     

Sucrose-Phosphate Synthase,Sucrose Synthase,and Invertase in Sugar Beet Leaves

The activity of sucrose-phosphate synthase (SPS) in sugar beet (Beta vulgaris L.) leaves was shown to exceed considerably the synthesizing activity of sucrose synthase (SS). The rise in SPS activity was related to the daylight period; i.e., it was associated with the rate of photosynthesis. The highest SPS activity was characteristic of fully expanded source leaves. In young developing leaves (leaves expanded to less than half of their final size), which represent the sink organs, the SPS activity was 2.5 times lower. At all stages of leaf development, the synthesizing SS activity was rather low. The diurnal change of SS activity was independent of photosynthesis and showed a slight rise from 6:00–8:00 p.m. Under field conditions, the highest SPS activity was found in leaves in the terminal stage of their development (105-day-old plants); the synthesizing activity of SS showed little changes during this period. The activity of soluble acid invertase was characteristic of young leaves. In mature leaves, the activity of this enzyme correlated with the daylight period. These changes occurred on the background of low sucrose content in leaves. The regulation of SPS, SS, and invertase activity is discussed. It is supposed that compartmentation of these enzymes in the photosynthesizing cell is important for transport, metabolism, and the osmotic function of sucrose in leaves.     

The effect of diabetes, nutritional factors, and sex on rat liver and kidney mevalonate kinase, mevalonate-5-phosphate kinase, and mevalonate-5-pyrophosphate decarboxylase

Isopycnic sucrose gradient separation of rat liver organelles revealed the presence of two distinct branched-chain α-keto acid decarboxylase activities; a mitochondrial activity, which decarboxylates the three branched-chain α-keto acids and requires CoA and NAD⁺ and a cytosolic activity, which decarboxylates α-ketoisocaproate, but not α-ketoisovalerate, or α-keto-β-methylvalerate. The latter enzyme does not require added CoA or NAD⁺. Assay conditions for the cytosolic α-ketoisocaproate decarboxylase activity were optimized and this activity was partially characterized. In rat liver cytosol preparations this activity has a pH optimum of 6.5 and is activated by 1.5 m ammonium sulfate. The decarboxylase activity has an apparent K_m of 0.03 mm for α-ketoisocaproate when optimized assay conditions are employed. Phenylpyruvate is a very potent inhibitor. α-Ketoisovalerate, α-keto-β-methylvalerate, α-ketobutyrate, and α-ketononanoate also inhibit the α-ketoisocaproate decarboxylase activity. The data indicate that the soluble α-ketoisocaproate decarboxylase is an oxidase. Rat liver cytosol preparations consumed oxygen when either α-ketoisocaproate or α-keto-γ-methiolbutyrate were added. None of the other α-keto acids tested stimulated oxygen consumption. 1-¹⁴C-Labeled α-keto-γ-methiolbutyrate is also decarboxylated by cytosol preparations. The α-ketoisocaproate oxidase was purified 20-fold from a 70,000g supernatant fraction of a rat liver homogenate. In these preparations the activity was increased 4-fold by the addition of dithiothreitol, ferrous iron, and ascorbate. The major product of this enzyme activity is β-hydroxyisovalerate. Isovalerate is not a free intermediate in the reaction. The data indicate an alternative pathway for metabolism of α-ketoisocaproate which produces β-hydroxyisovalerate.     

Transglutaminase Activity in Rat Brain: Characterization, Distribution, and Changes with Age

The activity of transglutaminase was characterized in the rat brain. In adults, comparable levels of transglutaminase activity are present in all brain regions examined. The activity is present in all subcellular fractions, as studied by differential centrifugation, but the soluble fraction contains the highest specific activity. The endogenous activity (enzyme activity assayed in the absence of the exogenous substrate casein) is very low in all subcellular fractions, except in the synaptosomal fraction where its highest levels are about 40-60% of the activity assayed in the presence of casein. Furthermore, enzyme activity is present on the external surface of synaptosomes. In the soluble fraction, maximal activity can be detected between pH values of 9 and 10 when assayed in the presence of 5 mM CaCl2 (with half-maximal activity requiring 0.75 mM CaCl2) and 0.4 mM putrescine (with an apparent Km for putrescine of 0.1 mM). The activity can be partially inhibited by ZnCl2 (with an IC50 of 4.5 mM) and by AlCl3 (with an IC50 of 5.1 mM). In the cerebellum, where the full span of neuronal development can be studied after birth, the highest specific activity is observed just after birth, thereafter the activity starts to decline and by 14 days, after a reduction of about 65%, it reaches levels observed throughout life.     

Regulation of invertase levels in Avena stem segments by gibberellic Acid, sucrose, glucose, and fructose

Gibberellic acid and sucrose play significant roles in the increases in invertase and growth in Avena stem segments. About 80% of invertase is readily solubilized, whereas the rest is in the cell wall fraction. The levels of both types of invertase change in a similar manner in the response to gibberellic acid and sucrose treatment. The work described here was carried out with only the soluble enzyme. In response to a treatment, the level of invertase activity typically follows a pattern of increase followed by decrease; the increase in activity is approximately correlated with the active growth phase, whereas the decrease in activity is initiated when growth of the segments slows. A continuous supply of gibberellic acid retards the decline of enzyme activity. When gibberellic acid was pulsed to the segments treated with or without sucrose, the level of invertase activity increased at least twice as high in the presence of sucrose as in its absence, but the lag period is longer with sucrose present. Cycloheximide treatments effectively abolish the gibberellic acid-promoted growth, and the level of enzyme activity drops rapidly. Decay of invertase activity in response to cycloheximide treatment occurs regardless of gibberellic acid or sucrose treatment or both, and it is generally faster when the inhibitor is administered at the peak of enzyme induction than when given at its rising phase. Pulses with sucrose, glucose, fructose, or glucose + fructose elevate the level of invertase significantly with a lag of about 5 to 10 hours. The increase in invertase activity elicited by a sucrose pulse is about one-third that caused by a gibberellic acid pulse given at a comparable time during mid-phase of enzyme induction, and the lag before the enzyme activity increases is nearly twice as long for sucrose as for gibberellic acid. Moreover, the gibberellic acid pulse results in about three times more growth than the sucrose pulse. Our studies support the view that gibberellic acid, as well as substrate (sucrose) and end products (glucose and fructose), play a significant role in regulating invertase levels in Avena stem tissue, and that such regulation provides a mechanism for increasing the level of soluble saccharides needed for gibberellic acid-promoted growth.     

重组GluV8的克隆表达、纯化及酶学性质研究

谷氨酰内切酶在生物制药及检测中应用较多,但来源受限,将全基因合成的金黄色葡萄球菌来源的谷氨酰内切酶功能区部分对应的基因进行改造后,克隆入表达载体pGEX-4T-2,导入E.coli BL21（DE3）,重组蛋白以可溶性形式表达。采用亲和层析等纯化步骤对重组蛋白进行纯化,用底物Z-Phe-Leu-Glu-pNA（L-2135）对重组蛋白的酶学性质进行了研究,用HPLC、LC-MS/MS检测方法对酶切融合蛋白的位点特异性进行了鉴定。结果表明该酶的相对活性为1568U/mg,最适作用温度为42℃、最适作用pH为8.0,在pH 9.0,50℃时仍有较高的酶活,将该酶与胰酶酶切融合蛋白所得肽段结合能够提升质谱检测结果的精确度。以上结果表明该重组酶具有良好的应用前景。     

Actin filament capping and cleaving activity of cytochalasins B, D, E, and H

The concentration dependences of the activities of cytochalasin B, D, E, and H in capping and cleaving actin filaments have been assayed using fluorescence photobleaching recovery. Filament capping was detected by the increase in mobile G-actin. Cytochalasin D (CD) showed the strongest filament capping activity, with an apparent dissociation constant from filament ends of 50 nM. The order of capping activity was CD greater than CH greater than CE much greater than CB. Filament cleavage was detected by the increase in the diffusion coefficients of actin filaments. By this criterion the order of filament cleavage activity was CD, CE greater than CH much greater than CB. Cytochalasin B shows some activity in cleavage of filaments over a concentration range (0-100 microM) at which it shows no appreciable capping activity. This activity, together with results from other groups, is interpreted to mean that CB binds to protomers within the filament, but not to the barbed end. The reversal of activities for CH and CE, combined with the activity profile of CB, constitute the strongest evidence to date that there is more than one cytochalasin binding site on the actin molecule.     

Nitrate reductase activity,biomass, yield,and quality in cotton in response to nitrogen fertilization

In the production of cotton (Gossypium hirsutum L.), nitrogen fertilization is one of the most costly crop practices, but important to reach high yields. However, high nitrogen (N) content in plants does not always translate into a high fibre production. One way of assessing the efficiency of the N fertilizer is through the enzymatic activity of the nitrate reductase (NR). This is a key enzyme in N assimilation, whose activity is regulated by a number of endogenous and exogenous factors that determine yield. The aim of this study was to assess the effect of N fertilization on yield, fibre quality, biomass, and NR enzymatic activity in vivo in the cotton variety Fiber Max 989. The evaluated application rates were 0, 50, 100, and 150 kg/ha of N, using urea as a source (46% N) in a randomizedblock design with three replicates. At harvest, the maximum yield of seed cotton and the greatest accumulation of total foliar biomass through time was reached after applying 150 kg N/ha. The different N-application rates did not affect the components of cotton-fibre quality. The activity of endogenous NR was greater on plants where 150 kg N/ha were applied. The highest cotton yield and N contents were obtained on these plants. Therefore, the NR activity in vivo could be used as a bioindicator of the N nutritional level in cotton.     

Regulation of activity of an ATP-dependent protease, Clp, by the amount of a subunit, ClpA, in the growth of Escherichia coli cells

The activity of an ATP-dependent protease, Clp, was examined in Escherichia coli SG1110 (lon-) in various growth phases. The ATP-dependent proteolytic activity (Clp activity) in a crude extract of the cells changed with the growth phase. Cells in the early exponential growth phase showed the lowest activity, but then the activity increased dramatically with cell growth. The highest Clp activity was found in the cells in the late exponential and early stationary phases, however, the activity returned to the original level on prolonged culturing. These changes in Clp activity were closely correlated to the amount of one of the components of Clp, Clp A, which was quantitated immunochemically with antibodies against the Clp A protein. However, the amount of the other component of Clp, Clp P, did not change with the growth phase. These results suggest that the activity of Clp in the cells is regulated by the amount of Clp A in various growth phases. We next examined the effect of the cellular ATP level on Clp activity, because ATP is a cofactor for Clp protease in vitro. The addition of dinitrophenol (DNP) and sodium azide reduced the intracellular concentration of ATP, but had no effect on the Clp activity or the level of the Clp A protein when these drugs were added to the culture at the stationary phase. On the other hand, these drugs elevated both the Clp activity and the Clp A amount in exponentially growing cells, whose cellular ATP level was also reduced.(ABSTRACT TRUNCATED AT 250 WORDS)     

Tyrosyltubulin ligase activity in brain,skeletal muscle,and liver of the developing chick

The developmental course of tyrosyltubulin ligase activity has been measured in three tissues of the embryonic chick: skeletal muscle; whole brain; and liver. There is a sharp peak in enzyme activity in muscle at day 13 when myotube formation is proceeding rapidly. In brain, high activities are maintained over a prolonged period. Liver has relatively little activity which decreases steadily over the entire developmental period that was examined. The possible relationship between high levels of tyrosyltubulin ligase activity and morphological changes dependent upon microtubule formation is discussed.     

Peptidyl-alpha-hydroxyglycine alpha-amidating lyase. Purification, characterization, and expression

The production of alpha-amidated peptides from their glycine-extended precursors is a two-step process involving the sequential action of two catalytic domains encoded by the bifunctional peptidylglycine alpha-amidating monooxygenase (PAM) precursor. The NH2-terminal third of the PAM precursor contains the first enzyme, peptidylglycine alpha-hydroxylating monooxygenase (PHM), a copper, molecular oxygen, and ascorbate-dependent enzyme. The middle third of the PAM precursor contains the second enzyme, peptidyl-alpha-hydroxyglycine alpha-amidating lyase (PAL). The COOH-terminal third of the PAM precursor encodes a transmembrane domain and a hydrophilic domain that may form a cytoplasmic tail. Antisera to a peptide within the PAL domain were used to identify a 50-kDa protein as the major form of PAL in bovine neurointermediate pituitary granules. This 50-kDa PAL protein was purified and found to begin at Asp434 of bPAM, indicating that it could arise through endoproteolytic cleavage of the bPAM precursor at Lys432-Lys433. With alpha-N-acetyl-Tyr-Val-alpha-hydroxyglycine as the substrate, PAL exhibits a pH optimum of 5.0; enzymatic activity is inhibited by high concentrations of salt but is relatively resistant to thiol reagents and urea. PAL activity is inhibited by EDTA and restored by a number of divalent metals, including Cd2+, Cu2+, Zn2+, and Ca2+. Kinetic studies using alpha-N-acetyl-Tyr-Val-alpha-hydroxyglycine indicate that PAL has a Km of 38 microM and a turnover number of 220/s. Expression vectors encoding only the soluble PHM domain or the PAM precursor from which the PHM domain had been deleted were constructed. hEK293 cells transfected with the PHM vector exhibited a 10-fold increase in secretion of PHM activity with no PHM activity detectable in control or transfected cells. hEK293 cells transfected with the PAL vector exhibited a 2-fold increase in secretion of PAL activity and a 15-fold increase in cellular PAL activity. Most of the PAL activity produced by the transfected cells remained membrane-associated.     

C-peptide,Na+,K+-ATPase,and Diabetes

Na⁺,K⁺-ATPase is an ubiquitous membrane enzyme that allows the extrusion of three sodium ions from the cell and two potassium ions from the extracellular fluid. Its activity is decreased in many tissues of streptozotocin-induced diabetic animals. This impairment could be at least partly responsible for the development of diabetic complications. Na⁺,K⁺-ATPase activity is decreased in the red blood cell membranes of type 1 diabetic individuals, irrespective of the degree of diabetic control. It is less impaired or even normal in those of type 2 diabetic patients. The authors have shown that in the red blood cells of type 2 diabetic patients, Na⁺,K⁺-ATPase activity was strongly related to blood C-peptide levels in non–insulin-treated patients (in whom C-peptide concentration reflects that of insulin) as well as in insulin-treated patients. Furthermore, a gene-environment relationship has been observed. The alpha-1 isoform of the enzyme predominant in red blood cells and nerve tissue is encoded by the ATP1A1 gene.Apolymorphism in the intron 1 of this gene is associated with lower enzyme activity in patients with C-peptide deficiency either with type 1 or type 2 diabetes, but not in normal individuals. There are several lines of evidence for a low C-peptide level being responsible for low Na⁺,K⁺-ATPase activity in the red blood cells. Short-term C-peptide infusion to type 1 diabetic patients restores normal Na⁺,K⁺-ATPase activity. Islet transplantation, which restores endogenous C-peptide secretion, enhances Na⁺,K⁺-ATPase activity proportionally to the rise in C-peptide. This C-peptide effect is not indirect. In fact, incubation of diabetic red blood cells with C-peptide at physiological concentration leads to an increase of Na⁺,K⁺-ATPase activity. In isolated proximal tubules of rats or in the medullary thick ascending limb of the kidney, C-peptide stimulates in a dose-dependent manner Na⁺,K⁺-ATPase activity. This impairment in Na⁺,K⁺-ATPase activity, mainly secondary to the lack of C-peptide, plays probably a role in the development of diabetic complications. Arguments have been developed showing that the diabetesinduced decrease in Na⁺,K⁺-ATPase activity compromises microvascular blood flow by two mechanisms: by affecting microvascular regulation and by decreasing red blood cell deformability, which leads to an increase in blood viscosity. C-peptide infusion restores red blood cell deformability and microvascular blood flow concomitantly with Na⁺,K⁺-ATPase activity. The defect in ATPase is strongly related to diabetic neuropathy. Patients with neuropathy have lower ATPase activity than those without. The diabetes-induced impairment in Na⁺,K⁺-ATPase activity is identical in red blood cells and neural tissue. Red blood cell ATPase activity is related to nerve conduction velocity in the peroneal and the tibial nerve of diabetic patients. C-peptide infusion to diabetic rats increases endoneural ATPase activity in rat. Because the defect in Na⁺,K⁺-ATPase activity is also probably involved in the development of diabetic nephropathy and cardiomyopathy, physiological C-peptide infusion could be beneficial for the prevention of diabetic complications.     

Azurocidin, a Natural Antibiotic from Human Neutrophils: Expression, Antimicrobial Activity, and Secretion

The azurophil granules of human PMN contain four antibiotic proteins, the serprocidins, which have extensive homology to one another and to serine proteases. Azurocidin, a member of this family, is a 29-kDa glycoprotein with broad spectrum antimicrobial activity and chemotactic activity toward monocytes. Insect cells transfected with a baculovirus vector carrying azurocidin cDNA produced a recombinant azurocidin protein. We purified the recombinant azurocidin protein from the culture medium of the infected cells and showed that it retained the antimicrobial activity of the native neutrophil-derived molecule. In addition, we present evidence that a 49-amino-acid region of the recombinant azurocidin protein is required for its secretion from insect cells.     

Cloning,expression, and purification of mouse heparanase

Heparanase is an endoglucuronidase that plays an important role in tumor invasion and metastasis. A full-length heparanase gene was cloned from a mouse embryo cDNA library and determined to encode a protein of 535 amino acids that is 77% identical to human heparanase. The full-length mouse gene was stably expressed in NS0 myeloma cells. The recombinant mouse heparanase protein was purified to homogeneity from cell lysates by a combination of Con-A affinity chromatography, heparin affinity chromatography, and size exclusion chromatography. The purified protein consisted of a non-covalent heterodimer of 50- and 8-kDa polypeptides, similar to the human homolog. The protein was enzymatically active in assays using radiolabeled ECM and heparan sulfate as substrates. The maximum heparanase activity was observed at acidic conditions; however, significant activity was also detected at neutral pH. The enzymatic activity of mouse heparanase was blocked by known heparanase inhibitors.     

Biliverdin reductase activity in cattle, sheep, rabbits and rats

1. Biliverdin reductase (BVR) activity was measured in post-microsomal supernatants of livers of cattle, sheep, rabbits and rats. BVR activities in bovine and ovine livers were 4.7 and 5.0%, respectively, of rat liver activity. 2. The finding of BVR activity in ruminants is in contrast to a previous report and may be due to the use of a different assay system. 3. Lapine liver had the lowest BVR activity of only 0.37% of rat liver activity. 4. Increasing the available heme by phenylhydrazine administration did not induce increased hepatic or splenic BVR activity in rabbits. 5. Maximal BVR activities were attained using NADPH as cofactor at pH 8.7 in sheep and rabbits and at pH 8.4 in cattle. 6. Differing concentrations of bovine or human albumins enhanced or inhibited BVR activity quite differently in the various species. 7. The finding of a very low, but measurable BVR activity in lapine liver and spleen may explain, in part, why rabbits, unlike rats, cattle and sheep, excrete primarily biliverdin (70%) into bile.