Antibody to enzymes--a three-component system. Introduction: immunochemistry of enzymes

Substrate-dependent modulation of enzyme activity by allosteric effector antibodies

We investigate the kinetic effects of antibody variable domain fragments derived from heavy chain antibodies (VHH domains) that behave as allosteric effectors of the nucleoside hydrolase from Trypanosoma vivax (TvNH). Strikingly, these antibodies can stimulate or inhibit TvNH steady-state activity, depending on the substrate used. This effect was investigated in greater detail using steady-state and pre-steady-state kinetic experiments. The most potent allosteric effector, VHH 1589, inhibits certain steps on the TvNH catalytic pathway (e.g. N-glycosidic bond cleavage) but increases the rates of others (e.g. substrate and product release). For the natural nucleoside 7-methyl guanosine, where product ribose release is rate determining, the net effect of VHH 1589 binding is to increase k(cat). For the poor substrate pNPR, VHH 1589 causes chemistry (O-glycosidic bond cleavage) to become rate determining and both k(cat)/K(m) and k(cat) to decrease. Thus, the substrate-dependent effects of VHH 1589 binding are caused by differences in the relative rates of chemistry with respect to subsequent steps on the catalytic pathway for these two substrates. We discuss possible mechanisms for these kinetic effects and the implications for allosteric effector drug development.

Inhibition of adenovirus DNA synthesis in vitro by sera from patients with systemic lupus erythematosus

Sera containing antinuclear antibodies from patients with systemic lupus erythematosus (SLE) and related disorders were tested for their effect on the synthesis of adenovirus (Ad) DNA in an in vitro replication system. After being heated at 60 degrees C for 1 h, some sera from patients with SLE inhibited Ad DNA synthesis by 60 to 100%. Antibodies to double-stranded DNA were present in 15 of the 16 inhibitory sera, and inhibitory activity copurified with anti-double-stranded DNA in the immunoglobulin G fraction. These SLE sera did not inhibit the DNA polymerases alpha, beta, gamma and had no antibody to the 72,000-dalton DNA-binding protein necessary for Ad DNA synthesis. The presence of antibodies to single-stranded DNA and a variety of saline-extractable antigens (Sm, Ha, nRNP, and rRNP) did not correlate with SLE serum inhibitory activity. Methods previously developed for studying the individual steps in Ad DNA replication were used to determine the site of inhibition by the SLE sera that contained antibody to double-stranded DNA. Concentrations of the SLE inhibitor that decreased the elongation of Ad DNA by greater than 85% had no effect on either the initiation of Ad DNA synthesis or the polymerization of the first 26 deoxyribonucleotides.

MECHANISM OF ACTION OF STAPHYLOCCAL ALPHA-HEMOLYSIN. II. ANALYSIS OF THE KINETIC CURVE AND INHIBITION BY SPECIFIC ANTIBODY

Marucci, Americo A. (Upstate Medical Center, Syracuse, N.Y.). Mechanism of action of staphylococcal alpha-hemolysin. II. Analysis of the kinetic curve and inhibition by specific antibody. J. Bacteriol. 86:1189-1195. 1963.-At least two steps are necessary before the rabbit erythrocyte is lysed by staphylococcal alpha-hemolysin. The first step involves the reaction of alpha-hemolysin with the red cell. The second step, leading to the release of hemoglobin, is an intrinsic reaction of the damaged red cell and takes place without further participation of hemolysin. The speed of this intrinsic reaction is temperature-dependent. Erythrocytes taken from the same rabbit do not vary in their susceptibility to the alpha-hemolysin. From the results of the experiments described herein, a preliminary hypothesis on the mechanism of action of staphylococcal alpha-hemolysin is given.

Reaction of phosphofructokinase 2/fructose 2,6-bisphosphatase with monoclonal antibodies. A proof of the bifunctionality of the enzyme

Monoclonal antibodies were derived from mice immunized against homogeneous chicken liver phosphofructokinase 2/fructose 2,6-bisphosphatase. Of 112 clones, 30 were found to secrete antibodies that specifically reacted with the antigen in enzyme-linked immunoabsorbant assay (ELISA) while 17, which were ELISA-negative, produced antibodies that affected the enzymic activity of the antigen. Four clones were subcloned and used for an extensive investigation of the reaction of the corresponding antibodies with the supposedly bifunctional enzyme. A definite proof of the bifunctionality of the enzyme was obtained from the two following observations. First, the two activities were similarly retained by the four antibodies that had been coupled to Sepharose. Second, one of the antibodies inhibited both activities with the same efficiency. Furthermore, the antigen-antibody reaction led to the formation of aggregates with an apparent molecular mass of several megadaltons, showing that the two subunits of the antigen reacted with the same antibody and were therefore identical. The four monoclonal antibodies affected the activity of phosphofructokinase 2. This effect was seen as an up to 17-fold activation as well as an up to 85% inhibition. Only one of the four antibodies (antibody 10) had inhibitory effects on fructose 2,6-bisphosphatase, an effect which was in part explained by a decrease in the rate of formation of the intermediary phosphoenzyme. All the effects described above were obtained on both the chicken liver and the pigeon muscle enzymes but with lower doses of antibody in the case of the former enzyme. Antibody 10 was also shown to react with mouse liver phosphofructokinase 2/fructose 2,6-bisphosphatase, and with phosphofructokinase 2 from chicken brain, heart and testis and from frog skeletal muscle and liver. None of the four antibodies cross-reacted with phosphofructokinase 2 from Saccharomyces cerevisiae or from spinach leaves.

Activation and inhibition of phosphorylase kinase by monospecific antibodies against preparatively isolated alpha, beta and gamma subunits

Homogeneous alpha and beta subunits were isolated for the first time in preparative amounts in the presence of sodium dodecyl sulfate. Analysis by analytical polyacrylamide electrophoresis, sedimentation velocity, and immunoprecipitation with monospecific antibodies indicated homogeneity. The apparent molecular masses of the purified subunits as determined electrophoretically in the presence of dodecyl sulfate are: alpha = 140.2 +/- 2.1 kDa and beta = 123 +/- 1.8 kDa. Amino acid analyses show that per 100 mol amino acid the alpha-subunit has a higher serine content (Ser alpha/Ser beta = 1.32, Ser alpha/Ser gamma = 1.42) and a lower aspartic acid/asparagine (Asx) content (AsX alpha/Asx beta = 0.76, Asx alpha/Asx gamma = 0.90) than the beta and gamma subunits. Monospecific antibodies against the purified alpha, beta and gamma subunits were produced in sheep [J. Immunol. Methods (1984) 70, 193-209] and their action on the catalytic activity of non-activated phosphorylase kinase assayed. It can be shown that certain antibody fractions of anti-alpha, anti-beta and anti-gamma inhibit the Ca2+-dependent and Ca2+-independent activity at pH 6.8 as well as at pH 8.2. Other antibody fractions against the beta and gamma subunits however activate the Ca2+-dependent activity at pH 6.8 threefold to fourfold, although they inhibit the activity at pH 8.2. These antibodies lead to a ca. five fold increase in the pH 6.8/8.2 activity ratio. Activating anti-beta can even overcome the inhibitory action of anti-alpha at pH 6.8. A kinetic analysis shows that inhibition is the result of a mixed type mechanism whereas activation is due to a fivefold to tenfold increase in V for phosphorylase b. The results illustrate the importance of possibly large, concerted conformational changes of phosphorylase kinase. It appears that activation or inhibition can be triggered by the antibody binding to conformational determinants of a single subunit type leading to a structural alteration of the holoenzyme.

Generation, characterization and ELISA of monospecific antibodies against the subunits of a Ca2+-dependent protein kinase and a Ca2+-transport ATPase from rabbit skeletal muscle

Monospecific precipitating sheep antibodies were generated for the first time against the purified, homogeneous alpha-, beta- and gamma-subunits of the Ca2+-dependent protein kinase, phosphorylase kinase, from rabbit muscle. As reference, antibodies against the holoenzyme and the CA2+-transport ATPase of sarcoplasmic reticulum were induced. In all cases antibody titers could be quantitated (standard error 5-10%) by enzyme-linked immunosorbent assay. Differentiation of antibody binding was achieved by quantitative precipitation and complement fixation assays. In general maximal antibody titers were reached 56 days after primary immunization and high titers (approximately 5000) were maintained for several weeks. Anti-alpha, anti-beta and anti-gamma avidly precipitate the denatured subunits employed as immunogens as well as the native enzyme. No cross-reactivity between antibodies against a specific subunit and any of the other heterologous subunits was demonstrable in double immunodiffusion assays providing no evidence for immunologically identical sites on the alpha-, beta- and gamma-subunits. Since anti-alpha, anti-beta and anti-gamma strongly inhibit enzyme activity, it is likely that they do so primarily by sterically interfering with the binding of the large substrate phosphorylase b (Mr 2.0 X 10(5)) to phosphorylase kinase (Mr 1.3 X 10(6)). It cannot be excluded, however, that anti-beta and anti-gamma bind to the active sites on these 2 subunits.

Basis for decreased D-beta-hydroxybutyrate dehydrogenase activity in liver mitochondria from diabetic rats

Liver mitochondria from rats made diabetic with streptozotocin have a reduced level of D-beta-hydroxybutyrate dehydrogenase (BDH) activity and decreased ratios of oleic/stearic and arachidonic/linoleic acids in the phospholipids of the mitochondrial membrane. This altered activity and lipid environment result from insulin deprivation since maintenance of the diabetic rats on insulin leads to normal characteristics (J.C. Vidal, J.O. McIntyre, P.F. Churchill, and S. Fleischer (1983) Arch. Biochem, Biophys. 224, 643-658). In the present study, the basis for the reduced enzymatic activity of this lipid-requiring enzyme was analyzed using three approaches: (i) Purified D-beta-hydroxybutyrate, dehydrogenase was inserted into membranes from mitochondria, submitochondrial vesicles, and mitochondrial lipids extracted therefrom. The activation was the same and optimal irrespective of whether the preparations were derived from normal or diabetic rat liver. Therefore, the decreased activity does not appear to be referable to an altered lipid composition. (ii) BDH activity can be released from the mitochondria by phospholipase A2 digestion. The released activity was proportional to the endogenous activity in the submitochondrial vesicles from normal and diabetic membranes. (iii) The BDH activity in submitochondrial vesicles was titrated by inhibition with specific antiserum. Less enzyme was found in mitochondria from diabetic rats as compared with those from normal animals. Hence, the lowered enzymatic activity is due to decreased enzyme in the mitochondrial inner membrane and not to the modified lipid environment.

Immunoassay of enzymes--an overview

Immunochemical techniques with enzymes as the antigen have grown in frequency during the last few years. These techniques have allowed evaluation of enzymes in the presence of endogenous inhibitors. Among those enzymes measured by immunochemical techniques and which have found diagnostic application, mention will be made of alkaline phosphatase (with particular reference to the intestinal, placental, and Regan isoenzymes), lactate dehydrogenase (in which renewed interest has developed due to techniques for specifically measuring the LD-1 isoenzyme), aspartate aminotransferase (of which the cytosolic and mitochondrial forms can now be independently measured by immunochemical techniques), acid phosphatase (for which a specific immunochemical assay for the prostatic enzyme has been widely introduced in diagnostic laboratories), and creatine kinase (for which a variety of immunochemical techniques to measure the M- and B-subunits are now part of standard laboratory assays). Other enzymes which will be discussed in this review include phosphohexose isomerase, amylase, ribonuclease, and lysozyme (muramidase). Finally, the use of enzymes, particularly asparaginase, in the chemotherapy of cancer will be outlined.

Inhibition of adenovirus DNA synthesis in vitro by sera from patients with systemic lupus erythematosus

Sera containing antinuclear antibodies from patients with systemic lupus erythematosus (SLE) and related disorders were tested for their effect on the synthesis of adenovirus (Ad) DNA in an in vitro replication system. After being heated at 60 degrees C for 1 h, some sera from patients with SLE inhibited Ad DNA synthesis by 60 to 100%. Antibodies to double-stranded DNA were present in 15 of the 16 inhibitory sera, and inhibitory activity copurified with anti-double-stranded DNA in the immunoglobulin G fraction. These SLE sera did not inhibit the DNA polymerases alpha, beta, gamma and had no antibody to the 72,000-dalton DNA-binding protein necessary for Ad DNA synthesis. The presence of antibodies to single-stranded DNA and a variety of saline-extractable antigens (Sm, Ha, nRNP, and rRNP) did not correlate with SLE serum inhibitory activity. Methods previously developed for studying the individual steps in Ad DNA replication were used to determine the site of inhibition by the SLE sera that contained antibody to double-stranded DNA. Concentrations of the SLE inhibitor that decreased the elongation of Ad DNA by greater than 85% had no effect on either the initiation of Ad DNA synthesis or the polymerization of the first 26 deoxyribonucleotides.

Inhibition of rabbit tissue kininase by anti-(endo-oligopeptidase A) antibodies

Highly purified rabbit brain endo-oligopeptidase A injected into goats produced, after 60 days of immunization, antisera that specifically inhibit purified rabbit brain endo-oligopeptidase A. An immunoreactive kininase having the same specificity as rabbit brain endo-oligopeptidase A for bradykinin was detected in several rabbit tissues. The highest amount of this immunoreactive kininase was found in the 25000 g supernatant fraction (S fraction) of heart, liver, skeletal muscle, ovary, brain and testis homogenates, corresponding to 89, 86, 78, 59, 56 and 53% respectively of the whole kininase activity found in the S fraction.

Immunological studies on CTP:phosphocholine cytidylyltransferase from the livers of normal and choline-deficient rats

Chickens were immunized with the purified low-molecular-weight form of CTP:phosphocholine cytidylyltransferase from rat liver cytosol. The antiserum was obtained and fractionated to yield immunoglobulin. The antibodies specifically inhibited the enzymatic activity of the partially purified low-molecular-weight form of the enzyme from pH 6.0 to 8.5. Antibodies against the low-molecular-weight form of the enzyme cross-reacted with the high-molecular-weight form of the enzyme from cytosol as well as with the cytidylyltransferase associated with the microsomal fraction. The antibodies were used for the immunochemical determination of the amount of cytosolic phosphocholine cytidylyltransferase in the livers of normal and choline-deficient rats. The amount of enzyme in rat liver cytosol was not changed for at least 18 days of choline deficiency. The decrease in specific activity of the enzyme in choline-deficiency may be caused by factors other than adaptive changes in the level of enzyme.

Purification and parital characterization of two genetic variants of placental alkaline phosphatase

The two most common variants of placental alkaline phosphatase, the F and S variants, were purified to homogeneity and characterized. Their molecular weights were determined by equilibrium ultracentrifugation and sodium dodecylsufate polyacrylamide gel electrophoresis, which gave almost identical values for the two variants, 118,000 (F) and 119,000 (S). The amino acid compositions of F and S variants presented here are found to be very similar. Differences between the two variants were found in specific activity (160 U/mg for F and 250 U/mg for S), isoelectric point (IP - 4.5 for F and 4.7 for S), sedimentation coefficient (6.5 X 10(-13) sec for F and 6.4 X 10(-13) sec for S). Thus the structural differences observed for these enzyme variants seem to affect both the active site and the protein conformation.

Antigenicity of bovine milk xanthine oxidase in guinea pigs

Six female and four male albino guinea pigs were immunized with active purified xanthine oxidase of bovine milk mixed with equal volume of Freund's complete adjuvant. One male and one female were immunized with heat-inactivated xanthine oxidase mixed with equal volume of adjuvant. Two males and four females were controls and received a phosphate buffer mixed with equal volume of adjuvant. The mixtures were administered intradermally and subcutaneously at weekly intervals for 6 consecutive wk and blood samples collected weekly. The enzyme was antigenic by the coated tanned red blood cell method. After the third weekly immunization, precipitating antibodies were in the sera of animals that received the active enzyme. Hemagglutination titers increased during subsequent weeks and reached a maximum after the sixth weekly immunization. Antisera from animals immunized with heat-inactivated xanthine oxidase gave a positive response similar to that with animals immunized with the active enzyme. However, when the same antisera were tested with sheep red blood cells coated with heat-inactivated enzyme, no hemagglutination was observed. Ouchterlony double gel-diffusion tests showed that it may be possible to differentiate between antibodies elicited to active and heat-inactivated xanthine oxidase.

The localization of enzymes in tissue sections by immuno-histochemistry. Conventional antibody and mixed aggregation techniques

Methods for detecting enzymes in tissue sections by antibody techniques are reviewed. In all these techniques, sections are first incubated with antibody. The bound antibody is visualized in one of four ways: identifying a label such as fluorescein linked to the antibody; using a labelled anti-antibody; employing complement and labelled anti-complement; or making use of a mixed aggregation immuno-cytochemical method. The last technique consists of three steps. A section is first incubated with antiserum, and secondly with the soluble enzyme under investigation. Thirdly the desired enzyme is "stained" using a conventional cytochemical method. The method is specific since, for example, the soluble enzyme used in the second step can bind only to antigenic determinants which are identical to those of the enzyme localized in the tissue. Thus purification of antigen and antibody sources is simplified, and chemical modifications of the antigen and antibody are avoided. Antibody also acts as a selective fixative for tissue antigen. It will inhibit the catalytic activity of its antigen and, in this way, permit the enzyme activity arising after the reaction of tissue enzyme-antibody complex with soluble enzyme to be amplified selectively. The mixed aggregation immuno-cytochemical technique has been used successfully with membrane-bound enzymes and cytoplasmic enzymes and for the demostration of catalytically inactive enzyme precursors.

Interactions of antisera, sera, and oral fluid with glucosyltransferases

Partially purified glucosyltransferases (GTF) isolated from Streptococcus mutans OMZ 176 and respective rabbit antisera were used to study enzyme-antibody interactions. A comparison between sensitive serological techniques and a functional inhibition test based on a radioenzyme assay demonstrated that the latter test system was the only one that discriminated between different antisera. Positive reactions in high dilutions in the former test systems were explained by the involvement of non-GTF contaminants and/or antibodies against enzyme regions distant to the catalytic site. The minute cross-reactions between two enzyme fractions and the respective antisera in the functional inhibition test indicated that the two immunogens contained mainly GTF that differed in the structure of their catalytic region. Control rabbit sera, rat oral fluid, and insoluble and soluble glucans considerably activated the GTF eluted with a 0.5 M phosphate buffer from hydroxapatite. It is suggested that these enzymes had additional binding sites for macromolecules inherent to rabbit sera and rat oral fluid, respectively, and that the observed increase in enzyme activity was due to a more stable enzyme conformation. Possibly the stimulation of GTF by the soluble glucan fraction was caused by a primer and/or acceptor function; however, this was not the case of the insoluble glucan. A stable complex was formed in the absence of the enzyme substrate, sucrose, the activity of which was not readily enhanced. It is concluded that the GTF of strain OMZ 176 are composed of multiple, multi-reactive molecules that enable these enzymes to act as cross-linking agents.

Antiserum raised against human pancreatic alpha-amylase

Isozymes of human pancreatic alpha-amylase were used as immunogens to raise antisera in rabbits. These antisera were unable to differentiate between the two isoamylases but produced an almost total inhibition of serum amylase activity when used at a dilution of 1 : 5000. Similar inhibition patterns were produced with the salivary and urinary enzymes as well as with serum from a patient with acute pancreatitis. No cross reactivity of the antisera with hog pancreatic amylase was observed and only at antiserum concentrations of 1 : 5000 and above was ther any inhibition of monkey serum amylase. The degree of inhibition observed varied with the size of the substrate but was not increased by the use of a second antibody.

Immunological properties of N-acetyl-beta-D-glucosaminidase of normal human liver and of GM2-gangliosidosis liver

Antisera were raised to a partially purified preparation of human liver hexosaminidase and to highly purified preparations of hexosaminidase isoenzymes A and B. All the antisera precipitated the enzyme in an enzymically active form, which could be located on immunodiffusion and immunoelectrophoretic gels by using a histochemical substrate. The antisera to the purified isoenzymes were shown to react with hexosaminidase from human liver, kidney, brain and spleen, but did not cross-react with human liver beta-glucosidase, beta-galactosidase, alpha-mannosidase, beta-xylosidase, arylsulphatase or acid phosphatase. Hexosaminidases A and B were immunologically identical. The immunological properties of the hexosaminidases from livers of patients with three types of GM(2)-gangliosidoses were closely similar. No evidence could be found for cross-reacting material in enzyme-deficient states.

Hybridization of variants of chloramphenicol acetyltransferase specified by fi + and fi - R factors

An fi(-) type of R factor for transferable chloramphenicol resistance carries the structural gene for a novel species of chloramphenicol acetyltransferase (EC 2.3.1.99). The enzyme associated with the fi(-) plasmid is distinct from that described for fi(+) R factors. The fi(+)- and fi(-)-related variants of chloramphenicol acetyltransferase were hybridized in vivo and in vitro. Both techniques yielded only a single symmetrical heteromeric species rather than the three (A(3)B(1), A(2)B(2), and A(1)B(3)) hybrids predicted from the tetrameric (identical monomers) structure of chloramphenicol acetyltransferase.

Protease and ribonuclease activities in bovine pituitary lobes

1. Acid and alkaline protease activities in bovine anterior and posterior pituitary lobes were reinvestigated by measurement of u.v. and Folin-Ciocalteu colour values of trichloroacetic acid-soluble digestion products of denatured haemoglobin. 2. Both lobes of the pituitary gland contain a cathepsin with a pH optimum at 3.8. 3. When release of u.v.-absorbing material was used as the assay there was also an optimum at pH8.3-9.7, but this proved to be due to the release of nucleosides from an endogenous substrate. 4. The presence of a ;cyclizing' ribonuclease active at alkaline pH on endogenous RNA was confirmed by the inhibitory effects of phosphate, arsenate and bentonite. The activity was unaffected by heat, EDTA or metal ions. The enzyme also acted on exogenous RNA. 5. A purified preparation of neurosecretory granules from fresh bovine posterior pituitary lobes was free from alkaline ribonuclease activity. Most of the activity present in the tissue was recovered in the supernatant plus microsomal material. 6. The distribution of RNA did not follow that of the alkaline ribonuclease.

Characterization of chloramphenicol acetyltransferase from chloramphenicol-resistant Staphylococcus aureus

Chloramphenicol-resistant strains of Staphylococcus aureus contain an inducible enzyme which inactivates chloramphenicol by acetylation in the presence of acetyl coenzyme A. The products of acetylation are chromatographically indistinguishable from those obtained with chloramphenicol-resistant Escherichia coli harboring an R factor. The kinetics of induction of chloramphenicol acetyltransferase are complicated by the inducer's effect on protein biosynthesis and its fate as chloramphenicol 3-acetate, which is not an inducer of the enzyme. The E. coli and S. aureus enzymes have been compared, with the conclusion that they are identical with respect to molecular weight (approximately 78,000) and pH optimum (7.8), but differ with respect to heat stability, substrate affinity, electrophoretic mobility, and immunological reactivity. Antiserum prepared against enzyme from E. coli contains precipitating antibody, which inactivates the E. coli enzyme, but neither precipitates nor neutralizes the activity of S. aureus enzyme.