Glycerol kinase activities in muscles from vertebrates and invertebrates

1. Glycerol kinase (EC 2.7.1.30) activity was measured in crude extracts of skeletal muscles by a radiochemical method. The properties of the enzyme from a number of different muscles are very similar to those of the enzyme from rat liver. Glycerol kinase from locust flight muscle was inhibited competitively by l-3-glycerophosphate with a K(i) of 4.0x10(-4)m. 2. The activity of glycerol kinase was measured in a variety of muscles from vertebrates and invertebrates in an attempt to explain the large variation in the activity of this enzyme in different muscles. 3. In vertebrates glycerol kinase activities were generally higher in red muscle than in white muscle; the highest activities (approx. 0.2mumole/min./g. fresh wt.) were found in the red breast muscle of some birds (e.g. pigeon, duck, blue tit) whereas the activities in the white breast muscle of the pheasant and domestic fowl were very low (approx. 0.02mumole/min./g.). 4. On the basis of glycerol kinase activities, muscles from insects can be classified into three groups: muscles that have a low enzyme activity, i.e. <0.3mumole/min./g. (leg muscles of all insects studied and the flight muscles of cockroaches and the tsetse fly); muscles that have an intermediate enzyme activity, i.e. 0.3-1.5mumoles/min./g. (e.g. locusts, cockchafers, moths, water-bugs); and muscles that have a high enzyme activity, i.e. >1.5mumoles/min./g. (e.g. bees, wasps, some blowflies). 5. The function of glycerol kinase in vertebrate and insect muscles that possess a low or intermediate activity is considered to be the removal of glycerol that is produced from lipolysis of triglyceride or diglyceride by the muscle. Therefore in these muscles the activity of glycerol kinase is related to the metabolism of fat, which is used to support sustained muscular activity. A possible regulatory role of glycerol kinase in the initiation of triglyceride or diglyceride lipolysis is discussed. 6. The function of glycerol kinase in the insect muscles that possess a high activity of the enzyme is considered to be related to the high rates of glycolysis that these muscles can perform. The oxidation of extramitochondrial NADH, and therefore the maintenance of glycolysis, is dependent on the functioning of the glycerophosphate cycle; if at any stage of flight (e.g. at the start) the rate of mitochondrial oxidation of l-3-glycerophosphate was less than the activity of the extramitochondrial glycerophosphate dehydrogenase, this compound would accumulate, inhibit the latter enzyme and inhibit glycolysis. It is suggested that such excessive accumulation of l-3-glycerophosphate is prevented by hydrolysis of this compound to glycerol; the latter would have to be removed from the muscle when the accumulation of l-3-glycerophosphate had stopped, and this would explain the presence of glycerol kinase in these muscles and its inhibition by l-3-glycerophosphate.     

Specificity and locale of the l-3-glycerophosphate–flavoprotein oxidoreductase of mitochondria isolated from the flight muscle of Sarcophaga barbata Thoms

1. The oxidation of l-3-glycerophosphate by flight-muscle mitochondria isolated from the flesh fly Sarcophaga barbata has been studied. Use of substrate analogues indicates that the catalytic and effector l-3-glycerophosphate binding sites on the allosteric l-3-glycerophosphate-flavoprotein oxidoreductase differ markedly in specificity. 2. The l-3-glycerophosphate-cyanoferrate oxidoreductase system in these mitochondria is antimycin-insensitive whereas the corresponding NADH-cyanoferrate oxidoreductase is extremely sensitive to this respiratory-chain inhibitor. Also no swelling is observed when these mitochondria are suspended in iso-osmotic solutions of ammonium glycerophosphate in contrast with the extensive swelling seen in similar solutions of ammonium pyruvate. These observations indicate that l-3-glycerophosphate does not penetrate the mitochondrial matrix whereas pyruvate does. 3. Submitochondrial particles catalyse the ATP-driven reduction of NAD(+) by l-3-glycerophosphate but at a far lower rate than that seen when succinate is the electron donor. These particles do not have an energy-linked pyridine nucleotide transhydrogenase activity. 4. We conclude that the l-3-glycerophosphate-flavoprotein oxidoreductase is located on the outer surface of the inner membrane of the flight-muscle mitochondria.     

Purification and properties of L-3-glycerophosphate dehydrogenase from pig brain mitochondria.

L-3-Glycerophosphate dehydrogenase (EC 1.1.99.5) was purified from pig brain mitochondria by extraction with deoxycholate, ion-exchange chromatography and (NH4)2SO4 fractionation in cholate, and preparative isoelectric focusing in Triton X-100. Sodium dodecyl sulphate/polyacrylamide gel electrophoresis shows that the purified enzyme consists of a single subunit of mol.wt. 75 000. The enzyme contains non-covalently bound FAD and low concentrations of iron and acid labile sulphide. No substrate reducible e.p.r. signals were detected. The conditions of purification, particularly the isoelectric focusing step, lead to considerable loss of FAD and possibly iron-sulphur centres. It is therefore not possible to decide with certainty whether the enzyme is a flavoprotein or a ferroflavoprotein. The enzyme catalyses the oxidation of L-3-glycerophosphate by a variety of electron acceptors, including ubiquinone analogues. A number if compounds known to inhibit ubiquinone oxidoreduction by other enzymes of the respiratory chain failed to inhibit L-3-glycerophosphate dehydrogenase, except at very high concentrations.     

Biochemical and immunological studies on an α-glycerophosphate dehydrogenase from the tephritid fly,Anastrepha suspensa

A rapid and efficient procedure has been developed for the purification of α-glycerophosphate dehydrogenase from the tephritid fly Anastrepha suspensa. This procedure is applicable to the isolation of the enzyme from other tephritids. The A. suspensa α-glycerophosphate dehydrogenase is dimeric with a molecular weight of 70,000 and a subunit molecular weight of 35,000. The pH optimum of the enzyme is 7.0. The amino acid composition is compared with that of other α-glycerophosphate dehydrogenases. By means of the quantitative microcomplement fixation procedure the A. suspensa α-glycerophosphate dehydrogenase is compared immunologically to a variety of other tephritid and dipteran α-glycerophosphate dehydrogenases.     

Acid phosphatases of rabbit spermatozoa: II. Partial purification and biochemical characterization of the multiple forms of rabbit spermatozoan acid phosphatase

Five acid phosphatases, S4, S3, S2, Szn and S1 (orthophosphoric monoester phosphohydrolase, EC 3.1.3.2) of ejaculated rabbit spermatozoa were either partially purified by DEAE-Sephadex column chromatography or prepared by specific extraction methods.The pH optimum of S4 was 6.0–6.5 in acetate buffer and 7.0 in Tris-HCl buffer; the pH optima of S3, S2, Szn, and S1 were 4.5, 5.5., 6.0 and 5.2, respectively, in acetate buffer. The apparent molecular weights of S3, S, Szn and S1, determined by disc gel electrophoresis, were 123 000, 86 000, 64 000 and 45 000–49 000, respectively. Incubation with neuraminidase did not alter the electrophoretic mobilities of any of the enzymes.Ten natural phosphoric esters were tested as substrates. S4 preferentially hydrolyzed ATP, ADP, PP_i and 3′-AMP. S3 hydrolyzed only β-glycerophosphate and glucose 6-phosphate to a significant extent. S2 hydrolyzed β-glycerophosphate, glucose 1-phosphate, the phosphoproteins, casein and phosvitin. S1 hydrolyzed ADP and β-glycerophosphate most readily. Szn may be an ATPase since it exhibits very high Zn²⁺-stimulated against ATP.These characteristics combined with the effects of NaF, ZnCl₂, l-(+)-tartaric acid, and formaldehyde on the activity of each partially purified enzyme with α-naphthyl phosphate as substrate indicate that these phosphatases are structurally and functionally different.     

Some properties of hepatic glycerol kinase and their relation to the control of glycerol utilization

1. Glycerol kinase (EC 2.7.1.30) is shown to catalyse a non-equilibrium reaction in rat liver; and, as it is the first enzyme in the pathway metabolizing glycerol, its properties may be pertinent to the metabolic regulation of glycerol uptake and utilization by this tissue. 2. The properties of hepatic glycerol kinase were studied by using a radiochemical technique to measure the enzyme activity. When the concentration of ATP is low the activity of glycerol kinase is inhibited by high concentrations of glycerol; but when the concentration of ATP is high there is no inhibition and the double-reciprocal plot is linear, providing a K(m) for glycerol of 3.16x10(-6)m. Glycerol kinase is activated by high ATP concentrations provided that the concentration of the second substrate (glycerol) is high; at low concentrations of glycerol ATP does not activate the enzyme so that the double-reciprocal plot is linear, providing a K(m) for ATP of 5.8x10(-5)m. It is suggested that these kinetics may be explained by a model similar to that described by Ferdinand (1966) for phosphofructokinase. 3. Hepatic glycerol kinase is inhibited by ADP and AMP, and raising the Mg(2+) concentration increases the inhibition by these two compounds; this suggests that ADP-Mg(2+) and AMP-Mg(2+) complexes are the inhibitory species. The physiological significance of these inhibitions may be to prevent phosphorylation of glycerol when the hepatic ATP concentration is low. It is suggested that this inhibition may provide an approach to the problem of measurement of rates of lipolysis by glycerol release in tissues that contain glycerol kinase (e.g. liver, kidney, muscle, adipose tissue). 4. Hepatic glycerol kinase is inhibited by l-3-glycerophosphate competitively with respect to glycerol. The physiological significance of this inhibition may be that factors that change the intracellular concentration of l-3-glycerophosphate could change glycerol uptake by the tissue. Thus it is suggested that thyroxine treatment or feeding rats on a diet high in glycerol, which increase the activity of glycerophosphate oxidase in liver and kidney cortex respectively, lead to an increased glycerol uptake through a decrease in the concentration of glycerophosphate in these tissues. It is known that ethanol administration decreases glycerol uptake by liver, and this can be explained by the increased concentration of l-3-glycerophosphate causing inhibition of glycerol kinase.     

Flavin-linked mitochondrial α-glycerophosphate dehydrogenase of Candida utilis

The 150-fold purification of the l-α-glycerophosphate dehydrogenase of Candida utilis electron-transport particles by very mild procedures is described. The active enzyme contains FAD, iron and copper. The function of the metals, if any, is not clear. Its molecular weight is about 5·10⁵. The subunit composition is complex and remains unresolved because the enzyme is contaminated with protease(s). The activity of this enzyme is very low in Saccharomyces cerevisiae unless the cells are grown in glycerol. The NAD-dependent cytoplasmic α-glycerophosphate dehydrogenase is present in C. utilis but could not be demonstrated in glucose-grown S. cerevisiae.     

Effect of l-triiodothyronine on the mitochondrial α-glycerophosphate dehydrogenase activity,mitochondrial and total protein contents of brain of Singi fish (Heteropneustes fossilis bloch)

A single injection of various doses (0.25, 0.5, 5, 20 and 50 μg/g) of l-triiodothyronine increased the mitochondrial cytochrome-linked α-glycerophosphate dehydrogenase (EC 1.1.99.5) activity and mitochondrial protein content of brain of Singi fish on the 3rd day. l-Triiodothyronine at the dose of 0.1 μg/g did not alter the α-glycerophosphate dehydrogenase activity and mitochondrial protein content of brain. The total protein content of the brain also increased on the 3rd day with 0.5 μg of l-triiodothyronine per g. Increased enzyme activity followed a dose-response relationship of a non-linear fashion. The enhancement of the α-glycerophosphate dehydrogenase activity of fish brain with a dose of 0.5 μg/g was found from the 1st day and it reached to a maximum level from the 3rd to the 5th day. The enzyme activity then sharply declined on the 6th or 7th day. Cycloheximide inhibited the l-triiodothyronine-induced increase in the α-glycerophosphate dehydrogenase activity, mitochondrial and total protein content of fish brain.The present study thus reveals the responsiveness of fish brain to thyroid hormone, and α-glycerophosphate dehydrogenase activity can be taken as a biochemical indices for the expression of thyroid hormone action in fish brain.     

The induction of mitochondrial L-3-glycerophosphate dehydrogenase by thyroid hormone

L-3-Glycerophosphate dehydrogenase was purified from porcine brain mitochondria by a shorter and simpler procedure than previously reported. Immunoblotting with antiserum to the porcine enzyme established that rat liver L-3-glycerophosphate dehydrogenase has the same Mr (76 000) by SDS-polyacrylamide gel electrophoresis. In liver mitochondria from normal and hyperthyroid rats, changes in L-3-glycerophosphate dehydrogenase activity were parallelled by changes in enzyme content assayed by immunoblotting. Similar changes were found in the amount of enzyme synthesised in vitro by reticulocyte lysate programmed with rat liver mRNA, suggesting that thyroid hormone causes specific induction of L-3-glycerophosphate dehydrogenase mRNA.     

Purification of L-3-glycerophosphate dehydrogenase from rat liver mitochondria

A rapid three-step procedure is presented for the purification of flavin-linked L-3-glycerophosphate dehydrogenase (E.C. 1.1.99.5.) from rat liver mitochondria. Solubilization of the enzyme is achieved selectively by digitonin, at a detergent-to-protein ratio of 0.7 mg/mg (mitochondrial protein concentration 10 mg/ml). The procedure involves chromatography on hydroxymethyl-hexamethylenediamine-succinyl-hexamethylenediamin e Sepharose 4B, followed by anion exchange chromatography using a FPLC technique. Subunit molecular weight of the enzyme was found to be 77,000 when prepared in the presence of the protease inhibitor phenylmethylsulphonyl fluoride. The Kmapp value for glycerophosphate was not influenced by the purification, and the ability of the enzyme to be activated by Ca2+ was preserved as well.     

Stimulation of rat renal Na+, K+-ATPase activity by thyroid hormones

The effect of thyroid hormones (T4, T3 and reverse T3) on rat renal Na+,K+-ATPase activity was investigated by a cytochemical technique. T3 caused stimulation of Na+,K+-ATPase activity in the renal medulla but not in the renal cortex. There was a peak in enzyme activity after cultured renal segments had been exposed to T3 for 11 min and this time of maximal stimulation did not vary with the concentration of T3. A rectilinear response in Na+,K+-ATPase activity was observed over T3 concentration range 10 pmol l-1 to 100 nmol l-1; at higher T3 concentrations, Na+,K+-ATPase activity was inhibited. The enzyme response was totally blocked by specific T3 antiserum. Addition of T4 and reverse T3 (100 fmol l-1 -1 mmol l-1) failed to stimulate Na+,K+-ATPase activity in any part of the kidney. Plasma (neat and diluted 1:10) stimulated the enzyme in parallel with the dose response curve and the stimulatory effect was abolished by prior addition of specific T3 antiserum.     

Purification and characteristics of a specific alkaline phosphatase from the integument of the mediterranean fruit fly,Ceratitis capitata

A specific alkaline phosphatase (ALPase) from the integument of white pupae has been purified 500-fold. The purification procedure included solubilization with Triton X-100, butanol extraction, fractionation with ammonium sulfate, and chromatography on concanavalin A-Sepharose, Sephadex G-200, and Sepharose 6B. Two peaks with enzyme activity were observed. The major peak had a molecular weight of approximately 180,000, while the minor peak, which had identical kinetic parameters and substrate specificity as those of the major one, was eluted in a high molecular weight form (about 900,000), probably cross-linked with chitin, since the enzyme was separated from the chitin only by lysozyme treatment. The enzyme hydrolyzes only tyrosine phosphate and β-glycerophosphate, with apparent K_ms of 0.35 mM and 0.22 mM, respectively, but not serine phosphate, threonine phosphate, ATP, and AMP. The optimum pH was in the alkaline range, with a peak at pH 9.4. The divalent cations Mn²⁺, Mg²⁺, and Ba²⁺ had stimulatory actions, while Cu²⁺ exerted a very strong inhibitory action on the enzyme activity. The ALPase was inhibited by L-tyrosine in a dose-dependent fashion. At a concentration of 2 mM, L-tyrosine totally inhibited the enzyme activity, while L-phenylalanine inactivated the enzyme about 25%. The accumulated evidence that ALPase is involved in the sclerotization process of insect integument is discussed.     

A method of isolation of partially purified alkaline peptide hydrolase from Drosophila melanogaster larvae

A semipreparative method is developed for preparing peptidohydrolase from Drosophila melanogaster larvae which involves the stages of extraction, salting-out, gel-filtration and ion-exchange chromatography. It is established that the maximal (up to 81%) yield of the enzyme is observed with the single extraction in the alkaline medium. The main bulk of the enzyme is salted-out in the low acid 3 M ammonium sulphate solution. Gel-filtration on column with Sephadex-25 provides complete salting-out of the enzyme-containing fraction, and ion exchange chromatography on CM-cellulose--a considerable purification of the enzyme under study. A degree of the obtained purification of the enzyme under study. A degree of the obtained peptidohydrolase preparation purity in acid and alkaline medium is determined by the method of electrophoresis in PAAG. At all stages of the preparation the enzyme possesses the casein-lytic activity and is able of hydrolyzing the ethyl ester and benzoyl arginine p-nitroanilide.     

Essentiality of coenzyme Q for the oxidation of -glycerophosphate by pig brain mitochondria

Serial extraction of lyophilized pig brain mitochondria with cold pentane resulted in complete loss of α-glycerophosphate oxidase activity. On titration with coenzyme Q₁₀ the activity was fully recovered. On comparing the decline of α-glycerophosphate, NADH, and succinoxidase activities during serial extraction with pentane, α-glycerophosphate oxidation was always the first to be lost. Extraction of coenzyme Q₁₀ from lyophilized brain mitochondria with pentane does not affect the activities of α-glycerophosphate or NADH dehydrogenase, but succinate dehydrogenase is partially inactivated. Reversible inactivation of the α-glycerophosphate oxidase system on depletion of the coenzyme Q content is taken as evidence that coenzyme Q is an obligatory component of this system. In accord with the conclusion that coenzyme Q is probably the physiological oxidant of α-glycerophosphate dehydrogenase, in antimycin-treated brain mitochondria α-glycerophosphate causes full activation of endogenous succinate dehydrogenase, in analogy to the previously observed activation by NAD-linked substrates in liver and heart mitochondria and by NADH in submitochondrial particles.     

Selective Extraction of Alkaline Phosphatase and 51 -Nucleotidase from Milk Fat Globule Membranes by a Single Phase n-Butanol Procedure

ABSTRACT

A single phase extraction procedure employing 8% (v/v) n-butanol at room temperature extracted over 90% of alkaline phosphatase activity and over 60% of 5'-nucleotidase activity from bovine milk fat globule membranes (MFGM). For 5'-nucleotidase, higher n-butanol concentrations lead to loss of activity, while lower concentrations were ineffective in extracting the enzyme. When extractions were performed at 0°C, similar yields were obtained for alkaline phosphatase extraction with 8% (v/v) n-butanol, but 5¹- nucleotidase extraction required 10% (v/v) n-butanol for similar yields. However, 5'-nucleotidase was less susceptible to denaturation during extraction at 0°C. The Km values and substrate specificities for both alkaline phosphatase and 5'-nucleotidase were unchanged by extraction with 8% (v/v) n-butanol. The 8% (v/v) n-butanol extraction procedure provides a 3-fold purification step, and an enzyme preparation suitable for further purification.     

The refolding of urea-denatured ribonuclease A is catalyzed by peptidyl-prolyl cis-trans isomerase

The refolding of urea-denatured ribonuclease A was measured at 0.31-3.1 mol . l-1 urea in the presence of various concentrations of peptidyl-prolyl cis-trans isomerase isolated from pig kidney. The rate of the slow CT-phase in the refolding reaction was found to be sensitive to this enzyme. A rate enhancement proportional to the isomerase activity has been observed. The activity of the enzyme was assayed with Glt-Ala-Ala-Pro-Phe-4-nitroanilide. The catalytic activity of the isomerase against unfolded ribonuclease is suppressed after preincubation of the enzyme with 0.001 mol . l-1 Cu2+, 0.01 mol . l-1 H+ and by heat inactivation. The results indicate the involvement of the cis/trans interconversion of proline peptide bonds during the refolding of ribonuclease A.     

Phospholipase A2 activity in human platelets. Isolation and purification of the enzyme

The activity of phospholipase A2 in blood platelets of healthy donors and IHD patients was examined. The enzyme activity was found to be increased 3-fold in platelets possessing a high level of functional activity (IHD) and by one order of magnitude in patients with myocardial infarction as compared with healthy donors. An enzyme preparation possessing a phospholipase activity was isolated from platelets by using salt extraction (KCl) and sonication. Purification of the enzyme by affinity chromatography resulted in two protein peaks both having a phospholipase A2 activity, the purification and molecular masses of these fractions being 768- and 2200-fold, and 13.5 and 15 kDa, respectively. It was supposed that these proteins are substrate-specific forms of phospholipase A2.     

Purification and Characterization of a Cation-stimulated Adenosine Triphosphatase from Corn Roots

A membrane-bound, monovalent cation-stimulated ATPase from Zea mays roots has been purified to a single band on sodium dodecyl sulfate gel electrophoresis. Microsomal preparations with K⁺ -stimulated ATPase activity were extracted with 1 m NaClO₄, and the solubilized enzyme was purified by chromatography on columns of n-hexyl-Sepharose, DEAE-cellulose, and Sephadex G-100 Superfine. A 500-fold purification over the activity present in the microsomes was obtained. The K⁺ -stimulated activity shows positive cooperativity with increasing KCl concentrations. The purified enzyme shows K⁺ -stimulated activity with ATP, GTP, UTP, CTP, ADP, α + β-glycerophosphate, p-nitrophenyl phosphate, and pyrophosphate as substrates. Under most conditions ATP is the best substrate. Although dicyclohexyl carbodiimide and Ca²⁺ inhibit and alkylguanidines stimulate the K⁺ -ATPase while bound to microsomes, they have no effect on the purified enzyme.     

The chemical nature of the products obtained by the action of cabbage-leaf phospholipase D on lysolecithin: the structure of lysolecithin

1. Lysolecithin, prepared by the action of snake-venom phospholipase A on ovolecithin, when incubated with Savoy-cabbage phospholipase D, in the presence of Ca(2+) ions, gave two degradation products (designated A and B) in the form of their calcium salts. 2. These calcium salts were separated quantitatively by solvent fractionation and converted into the corresponding sodium salts. 3. Substance B proved to be a lysophosphatidic acid of conventional structure (1-monoacyl-l-3-glycerophosphoric acid). When the phosphate group was removed by means of prostatic acid phosphomonoesterase, a 1-monoglyceride was formed quantitatively. Alkaline hydrolysis gave the theoretical yield of l-3-glycerophosphate. 4. Substance A, on the other hand, had all the properties expected for a cyclic phosphate of a 1-monoglyceride. It was unaffected by phosphomonoesterase. On alkaline hydrolysis, the acyl group was removed and ring opening of the presumed cyclic phosphate group gave an approximately equimolar mixture of 2- and l-3-glycerophosphates. 5. The structures of substances A and B confirm lysolecithin as 1-monoacyl-l-3-glycerylphosphorylcholine.     

Characterization of the Ca2+- or Mg2+-ATPase of transverse tubule membranes isolated from rabbit skeletal muscle

Transverse tubule membranes isolated from rabbit skeletal muscle have high levels of a Ca2+- or Mg2+-ATPase with Km values for Ca-ATP or Mg-ATP in the 0.2 mM range, but do not display detectable levels of ATPase activity activated by micromolar [Ca2+]. The transverse tubule enzyme is less temperature or pH dependent than the Ca2+-ATPase of sarcoplasmic reticulum and hydrolyzes equally well ATP, ITP, UTP, CTP, and GTP. Of several ionic, non-ionic, and zwitterionic detergents tested, only lysolecithin solubilizes the transverse tubule membrane while preserving ATPase activity. After extraction of about 50% of the transverse tubule proteins by solubilization with lysolecithin most of the ATPase activity remains membrane bound, indicating that the Ca2+- or Mg2+-ATPase is an intrinsic membrane enzyme. A second extraction of the remaining transverse tubule proteins with lysolecithin results in solubilization and partial purification of the enzyme. Sedimentation of the Ca2+- or Mg2+-ATPase, partially purified by lysolecithin solubilization, through a continuous sucrose gradient devoid of detergent leads to additional purification, with an overall 3- to 5-fold purification factor. The purified enzyme preparation contains two main protein components of molecular weights 107,000 and 30,000. Cholesterol, which is highly enriched in the transverse tubule membrane, copurifies with the enzyme. Transverse tubule membrane vesicles also display ATP-dependent calcium transport which is not affected by phosphate or oxalate. The possibility that the Ca2+- or Mg2+-ATPase is the enzyme responsible for the Ca2+ transport displayed by isolated transverse tubules is discussed.