Malic enzymes of salmon trout heart mitochondria: separation and some physicochemical properties of NAD-preferring and NADP-specific enzymes

Mitochondria isolated from the heart of the Baltic salmon trout Salmo trutta contain two distinct malic enzymes. One of these enzymes (NAD-preferring malic enzyme) catalyses the oxidative decarboxylation of malate in the presence of either NAD or NADP. The specific activity with NAD was six times that with NADP as coenzyme. The second enzyme is specific for NADP. These two malic enzymes have been separated by: ion exchange chromatography of DEAE-Sephacel, affinity chromatography on 2',5'ADP-Sepharose 4B, gel filtration on Sephacryl S-300 and polyacrylamide gel electrophoresis. The mol. wts of the two native malic enzymes determined by gel filtration were found to be 280,000 and 190,000 for NAD-preferring and NADP-specific malic enzyme, respectively. Chromatofocusing revealed the isoelectric points of the two enzymes at pH 5.45 and 5.85 for NAD-preferring and NADP-specific malic enzyme, respectively.

Concomitant purification of three porcine heart mitochondrial enzymes: citrate synthase, aspartate aminotransferase, and malate dehydrogenase

The mitochondrial enzymes citrate synthase, malate dehydrogenase, and aspartate aminotransferase were purified to homogeneity from porcine hearts by use of Bio-Rex 70, carboxymethylcellulose CM32, and Affi-Gel blue chromatography. This procedure provides relatively rapid, large-scale preparation of the three enzymes based on their differential binding to commercially available cation-exchange resins followed by a final affinity chromatography step.

Purification and properties of malolactic enzyme from Lactobacillus murinus CNRZ 313

The malolactic enzyme of Lactobacillus murinus was purified 79 fold. Mr = 220,000 as determined by gel filtration and gradient gel electrophoresis. The enzyme consists of two apparently identical subunits (Mr = 110,000) that were observed after treatment with sodium dodecyl sulfate. NAD protected the enzyme against inactivation and its addition, after dissociation, restored the malolactic activity. The apparent Km's for malate, NAD, and Mn2+ were 2.31 X 10(-2), 4.5 X 10(-4), and 1.4 X 10(-4) mM, respectively. Maximum enzymatic activity was observed at 37 degrees C and pH 5.5 in 0.2 M phosphate buffer. At pH values substantially different from the optimum, a positive cooperativity between substrate molecules was observed. The activation energy of the reaction was 8000 and 16,200 cal mol-1 for the temperature values more than and less than 30 degrees C, respectively. Malolactic enzyme catalyzes the NAD and manganese-dependent reaction L-malate----L-lactate + CO2. Therefore, this enzyme can be distinguished from the well-known malic enzymes [L-malate: NAD+ oxidoreductase, oxaloacetate decarboxylating (EC 1.1.1.38) or decarboxylating (EC 1.1.1.39)].

Rapid purification and radioimmunoassay of cytosolic malic enzyme

A very rapid and highly effective procedure has been devised for the isolation of homogeneous malic enzyme from rat liver cytosol. A combination of precipitation with 10 to 20% polyethylene glycol, ion-exchange chromatography on DEAE-cellulose, and affinity chromatography on Procion Red HE-3B Agarose was used to prepare 3 to 4 mg of homogeneous malic enzyme from the livers of two rats in 18 h. In addition to introducing the advantages of simplicity, speed, and high yield (31%) the new method eliminates potentially denaturing steps (heat treatment, ethanol fractionation) and prolonged dialysis procedures used in other purification schemes. Malic enzyme purified by this new method was use to immunize rabbits. The resulting antibodies bound purified rat liver and mouse liver malic enzymes with very similar affinities and also avidly complexed cytosolic malic enzyme from two murine cell lines, 3T3-L1 preadipocytes and 3T3-C2 fibroblasts. When purified malic enzyme was incubated with lactoperoxidase, glucose oxidase and Na 125I 1.8 atoms of 125I were incorporated per molecule of enzyme with full retention of catalytic activity, subunit size, and immunoreactivity. The antiserum, the purified enzyme, and enzymatically iodinated 125I-malic enzyme were used to construct a sensitive, competitive binding radioimmunoassay for the measurement of malic enzyme mass in the range of 1 to 100 ng.

Purification and properties of mitochondrial malate dehydrogenase from unfertilized eggs of the sea urchin, Anthocidaris crassispina

Purification and characterization of mitochondrial malate dehydrogenase [EC 1.1.1.37] from unfertilized eggs of the sea urchin, Anthocidaris crassispina, are described. The purification method consisted of dextran sulfate fractionation, Blue Dextran Sepharose chromatography, Phenyl-Sepharose hydrophobic chromatography and DEAE-cellulose chromatography. The enzyme was purified 771-fold with a 7% yield from the crude extract. The purified enzyme appeared homogeneous on polyacrylamide gel electrophoresis under both native and denatured conditions. After incubation at 45 degrees C for 50 min, the enzyme lost about 90% of its activity. In the presence of NADH, however, the enzyme was protected against the heat denaturation. The native enzyme had a molecular weight of about 65,000 and probably consisted of two identical subunits. In the reduction of oxaloacetate with NADH, a broad optimum pH ranging from 8.2 to 9.4 was found with 50 mM Tris-HCl and glycine-NaOH buffers. Sodium phosphate buffer apparently activated the enzyme. The apparent Km values for oxaloacetate and NADH were 19 microM and 30 microM, respectively. The optimum pH for malate oxidation with NAD+ was 10.2 in 50 mM NaHCO3-Na2CO3 buffer. The apparent Km values for malate and NAD+ were 7.0 mM and 0.6 mM, respectively. Zinc ion, sulfite ion, p-chloromercuriphenylsulfonate and adenine nucleotides strongly inhibited the enzyme.

Purification, kinetic behavior, and regulation of NAD(P)+ malic enzyme of tumor mitochondria

The purification and kinetic characterization of an NAD(P)+-malic enzyme from 22aH mouse hepatoma mitochondria are described. The enzyme was purified 328-fold with a final yield of 51% and specific activity of 38.1 units/mg of protein by employing DEAE-cellulose chromatography and an ATP affinity column. Sephadex G-200 chromatography yielded a native Mr = 240,000. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed a major subunit with Mr = 61,000, suggesting a tetrameric structure, and also showed that the preparation contained less than 10% polypeptide impurities. Use of the ATP affinity column required the presence of MnCl2 and fumarate (an allosteric activator) in the elution buffers. In the absence of fumarate, the Michaelis constants for malate, NAD+, and NADP+ were 3.6 mM, 55 microM, and 72 microM, respectively; in the presence of fumarate (2 mM), the constants were 0.34 mM, 9 microM, and 13 microM, respectively. ATP was shown to be an allosteric inhibitor, competitive with malate. However, the inhibition by ATP displayed hyperbolic competitive kinetics with a KI (ATP) of 80 microM (minus fumarate) and 0.5 mM (plus 2 mM fumarate). The allosteric properties of the enzyme are integrated into a rationale for its specific role in the pathways of malate and glutamate oxidation in tumor mitochondria.

Glycosomal and mitochondrial malate dehydrogenases in epimastigotes of Trypanosoma cruzi

The degradation of glucose by Trypanosoma cruzi leads to the excretion of succinate. Malate dehydrogenase (MDH) participates in this process by reducing to malate the oxaloacetate synthesized by the glycosomal enzyme, phosphoenolpyruvate carboxykinase. The best coupling for these two sequential reactions would be attained if both enzymes were placed in the same subcellular compartment. The intracellular distribution of the MDH activity in epimastigotes of T. cruzi was studied by two methods. Selective disruption of cellular membranes with increasing concentrations of digitonin, indicated that trypanosomal MDH is particulate. Isopycnic centrifugation in a sucrose gradient of a large granule fraction, obtained by grinding the cells with silicon carbide, showed the presence of two MDH activities: one banding together with the glycosomal marker phosphoenolpyruvate carboxykinase, the other with the mitochondrial marker citrate synthase. Isoelectrofocusing of cell-free extracts led to the separation of two enzyme forms, with pI values of about 3.5 (MDHa) and 9.4 (MDHb). These forms had similar molecular weights (approx. 60 000) and apparent Km values, but showed a small but consistent difference in their pH optima (9.23 for MDHa and 9.05 for MDHb), and in their activation by inorganic phosphate (apparent Ka values of 33 mM and 87 mM, for MDHa and MDHb, respectively). Determination of the pH optima of the enzyme forms separated by isopycnic centrifugation suggests that the glycosomal enzyme form is MDHa, and the mitochondrial one is MDHb.

Import of rat liver mitochondrial malate dehydrogenase. Synthesis, transport, and processing in vitro of its precursor

Rat liver total RNA was translated in a reticulocyte lysate, and the precursor of rat liver mitochondrial malate dehydrogenase was identified by a monospecific antibody against the denatured mature enzyme. The precursor is about Mr = 1500 to 2000 larger than the monomeric form of the mature protein. The major spots of the two-dimensional peptide map of the two proteins were identical. The precursor was synthesized on free polysomes, but not membrane-bound polysomes. Upon fractionation by molecular sieve chromatography on Sephadex G-100, the size of the precursor was slightly larger than the dimeric form of the mature protein. Incubation of the precursor with isolated mitochondria from Chinese hamster ovary cells resulted in uptake and processing of the precursor to the mature size. The processed form was resistant to trypsin indicating that it was translocated into mitochondria. Processing was complete in 10 to 30 min at 30 degrees C. Rapid binding of the precursor to mitochondria was also observed at 0 or 30 degrees C. Processing but not binding was inhibited by an uncoupler.

Kinetic properties of NAD malic enzyme from cauliflower

The kinetic characteristics of NAD malic enzyme purified to homogeneity from cauliflower florets have been examined. Free NAD+ is the active form of this coenzyme. Double-reciprocal plots of data obtained by varying NAD+ and malate2- at a saturating concentration of Mg2+ or by varying Mg2+ and NAD+ at a saturating level of malate2-are of intersecting type. This indicates that NAD malic enzyme obeys a sequential mechanism. Analysis of these sets of data suggests that each of these substrate pairs binds randomly to the enzyme. However, each substrate binds tighter when others are already present on the enzyme. NAD malic enzyme cannot decarboxylate malate2- in the absence of either Mg2+ or NAD+. Arrhenius plots of the NAD-linked reaction are concave downward, indicating the existence of two rate-determining steps with activation energies of 26.5 and 14.2 kcal/mol, respectively. In addition to Mg2+, the enzyme can also use Mn2+ and Co2+. Using Co2+ in place of Mg2+ does not change Vmax or Km, malate2- but the Km for metal and NAD+ are greatly decreased. At pH 7.0 and above, Mn2+ isotherms and malate2- curves with Mn2+ are nonlinear and appear to be composed of two separate saturation curves. NAD malic enzyme is completely and irreversibly inactivated by N-ethylmaleimide. The enzyme is also irreversibly inactivated approximately 50% by KCNO.

Malate dehydrogenases from actinomycetes: structural comparison of Thermoactinomyces enzyme with other actinomycete and Bacillus enzymes

Malate dehydrogenases from bacteria belonging to the genus Thermoactinomyces are tetrameric, like those from Bacillus spp., and exhibit a high degree of structural homology to Bacillus malate dehydrogenase as judged by immunological cross-reactivity. Malate dehydrogenases from other actinomycetes are dimers and do not cross-react with antibodies to Bacillus malate dehydrogenase.

Biochemical characterization of a 34-kilodalton normal cellular substrate of pp60v-src and an associated 6-kilodalton protein

Transformation of fibroblasts by several retroviruses that produce transforming gene products associated with protein kinase activity results in the phosphorylation of a normal cellular protein with an Mr of 34,000 (the 34K protein). Evidence is presented here that, as extracted from chicken embryo fibroblasts, this protein exists in two forms that differ both in their elution from hydroxylapatite and in their native molecular weight. The form that eluted from hydroxylapatite at 210 to 295 mM potassium phosphate displayed a native molecular weight of 30,000 to 40,000, whereas the form that eluted at 320 to 440 mM displayed a native molecular weight of 60,000 to 70,000. The latter form copurified with a low-molecular-weight protein with an approximate Mr of 6,000 (6K). Both forms of 34K were completely separable from malate dehydrogenase activity. Phosphorylated 34K, isolated from Rous sarcoma virus-transformed cells, was also present in two forms; hence, in the cell neither form serves as a preferential substrate for pp60v-src. We found that the expression of 34K differed greatly in various avian tissues. In particular, it was present in the highest concentration in cultured fibroblasts and in very low concentration in brain tissue. Its expression in this tissue seems to be controlled at the level of transcription, since 34K mRNA in brain tissue was barely detectable. The expression of 6K was similar to that of 34K.

Chromatographic behaviour of the molecular forms of guinea-pig skeletal muscle cytoplasmic malate dehydrogenase

The isolated molecular forms of guinea-pig skeletal muscle cytoplasmic malate dehydrogenase have a different chromatographic behaviour through affinity or hydrophobic interaction gels; in all cases the retention of the B form is more noticeable. Chromatography of a partly purified preparation through 5' AMP-Sepharose allows both molecular forms of malate dehydrogenase to be separated and obtained free from lactate dehydrogenase.

Role and location of NAD malic enzyme in thermogenic tissues of Araceae

This work was done to discover how those nonphotosynthetic tissues of the Araceae that become thermogenic release, as CO2, carbon recently fixed by phosphoenolpyruvate carboxylase. Extracts of clubs of the spadix of Arum maculatum showed no activity for phosphoenolpyruvate carboxykinase and low activities of NADP malic enzyme. NAD malic enzyme activity in the above extracts and in those of thermogenic tissues of other Araceae was appreciable. Analysis of homogenates of clubs of Typhonium giraldii by differential centrifugation and sucrose gradients showed that NAD malic enzyme was confined to mitochondria. Centrifugation of mitochondria after freezing and thawing left all the NAD malic enzyme in the supernatant. NAD malic enzyme in isolated, intact mitochondria was completely latent, and was completely protected from exogenous trypsin. The responses of this latency and protection to different concentrations of Triton X-100 suggested that none of the NAD malic enzyme was accessible from either the outside or the intermembrane space of the mitochondria. Treatment of excised clubs of A. maculatum with 2-N-butylmalonate largely prevented the development of the rapid respiration responsible for thermogenesis, and severely inhibited dark fixation of 14CO2. The conclusion is that in mature clubs of the Araceae phosphoenolpyruvate is converted to malate in the cytosol by phosphoenolpyruvate carboxylase and NAD malate dehydrogenase, and that this malate then enters the mitochondrial matrix where it is converted to pyruvate by NAD malic enzyme.

Properties and function of malate enzyme from Pseudomonas putida

Malate enzyme (L-malate: NADP+ oxidoreductase (oxalacetate-decarboxylating, EC 1.1.1.40)) has been purified from Pseudomonas putida to 99 per cent homogeneity by heat, ammonium suphate fractionation, gel filtration and anion exchange chromatography. Sodium dodecylsulphate-(SDS)-polyacrylamide disc gel electrophoresis analysis showed an approximate tetrameric subunit with a molecular weight of 52,000. The purified enzyme showed a pH optimum between 8.0 and 8.5 (for Tris-HCl buffer) and required bivalent cations for catalysis; monovalent ions like K+ and NH4+ acted as very effective activators. The temperature-activity relationship for the malate enzyme from 35-80 degrees C showed broken Arrhenius plots with an inflexion at 65 degrees C. The enzyme halflife was 30s at 85 degrees C. The enzyme showed hyperbolic kinetics for both substrates with apparent Km values of 4.0 X 10(-4) M and 2.3 X 10(-5) M for L-malate and NADP+ respectively. From the study of the effects of some compounds on the enzyme, the physiological significance of those produced by fumarate, succinate and oxalacetate can be emphasized.

A facile method for the isolation of porcine heart mitochondrial malate dehydrogenase by affinity elution chromatography on Procion Red HE3B

A quick, simple method has been devised for isolating pig heart mitochondrial malate dehydrogenase in apparently homogeneous state and good yield. It entails the adsorption of the enzyme to agarose-linked Procion Red HE3B and specific elution of a ternary complex consisting of the malate dehydrogenase, NAD+, and L-malate.

The conformation of mitochondrial malate dehydrogenase derived from an electron density map at 5.3-A resolution

A monoclinic form of crystalline porcine heart mitochondrial malate dehydrogenase has been prepared and contains two dimers in the asymmetric unit. The analysis of single crystal x-ray data shows that the two dimers are packed in the crystal lattice as a tetramer with approximate 222-point symmetry. Heavy atom derivatives using the compounds ethylmercurithiosalicylic acid and IrCl3 have been characterized and multiple isomorphous replacement methods have been used to obtain an electron density map at 5.3-A resolution. The phasing of the x-ray data was aided by including contributions from crystal forms with and without the coenzyme, NAD+. By using electron density averaging methods, the quality of the low resolution electron density map was improved to the point where it was possible to establish the overall conformation of mitochondrial malate dehydrogenase. The results confirm the proposed similarities between the mitochondrial and cytoplasmic forms of the malate dehydrogenases. Studies using x-ray data from the apo- and holo-forms of the enzyme describe the location of the active site as well as the arrangement of subunits in the tetrameric crystalline form of the enzyme.

Linkage group V of platyfishes and Swordtails of the genus Xiphophorus (Poeciliidae): linkage of loci for malate dehydrogenase-2 and esterase-1 and esterase-4 with a gene controlling the severity of hybrid melanomas

Electrophoretic variations ascribable to three enzyme loci coding for esterase-1 and -4 (ES1 and ES4) and a malate dehydrogenase-2 isozyme (MDH2) were studied in interspecific backcrosses of fishes of the genus Xiphophorus (Poeciliidae). Normal segregation was demonstrated for all three loci. Linkage analyses indicated a gene order of ES1-6%-ES4-33%-MDH2. This group [designated linkage group (LG) V] was shown to assort independently from the 11 loci comprising LG's I-IV and from 18 other informative markers, with the limits of the data. A factor controlling the extent of development of inherited melanomas was demonstrated to be associated only with LG V loci, implying predominant control by a single gene, which probably determines the completeness of differentiation of macromelanophores in hybrids. Possible explanations for variability in the apparent chromosomal position of the melanoma severity gene, as assessed by estimates of recombination with the LG V enzyme loci, are discussed.

Human liver cytosolic malate dehydrogenase: purification, kinetic properties, and role in ethanol metabolism

Cytosolic malate dehydrogenase from human liver was isolated and its physical and kinetic properties were determined. The enzyme had a molecular weight of 72,000 +/- 2000 and an amino acid composition similar to those of malate dehydrogenases from other species. The kinetic behaviour of the enzyme was consistent with an Ordered Bi Bi mechanism. The following values (microM) of the kinetic parameters were obtained at pH 7.4 and 37 degrees C: Ka, 17; Kia, 3.6; Kb, 51; Kib, 68; Kp, 770; Kip, 10,700; Kq, 42; Kiq, 500, where a, b, p, and q refer to NADH, oxalacetate, malate, and NAD+, respectively. The maximum velocity of the enzyme in human liver homogenates was 102 mumol/min/g wet wt of liver for oxalacetate reduction and 11.2 mumol/min/g liver for malate oxidation at pH 7.4 and 37 degrees C. Calculations using these parameters showed that, under conditions in vivo, the rate of NADH oxidation by the enzyme would be much less than the maximum velocity and could be comparable to the rate of NADH production during ethanol oxidation in human liver. The rate of NADH oxidation would be sensitive to the concentrations of NADH and oxalacetate; this sensitivity can explain the change in cytosolic NAD+/NADH redox state during ethanol metabolism in human liver.

Purification and characterization of a bifunctional L-(+)-tartrate dehydrogenase-D-(+)-malate dehydrogenase (decarboxylating) from Rhodopseudomonas sphaeroides Y

A bifunctional enzyme, L-(+)-tartrate dehydrogenase-D-(+)-malate dehydrogenase (decarboxylating) (EC 1.1.1.93 and EC 1.1.1. . . , respectively), was discovered in cells of Rhodopseudomonas sphaeroides Y, which accounts for the ability of this organism to grow on L-(+)-malate. The enzyme was purified 110-fold to homogeneity with a yield of 51%. During the course of purification, including ion-exchange chromatography and preparative gel electrophoresis, both enzyme activities appeared to be in association. The ratio of their activities remained almost constant [1:10, L-(+)-tartrate dehydrogenase/D-(+)-malate dehydrogenase (decarboxylating)] throughout all steps of purification. Analysis by polyacrylamide gel electrophoresis revealed the presence of a single protein band, the position of which was coincident with both L-(+)-tartrate dehydrogenase and D-(+)-malate dehydrogenase (decarboxylating) activities. The apparent molecular weight of the enzyme was determined to be 158,000 by gel filtration and 162,000 by ultracentrifugation. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis yielded a single polypeptide chain with an estimated molecular weight of 38,500, indicating that the enzyme consisted of four subunits of identical size. The isoelectric point of the enzyme was between pH 5.0 and 5.2. The enzyme catalyzed the NAD-linked oxidation of L-(+)-tartrate as well as the oxidative decarboxylation of D-(+)-malate. For both reactions, the optimal pH was in a range from 8.4 to 9.0. The activation energy of the reaction (delta Ho) was 71.8 kJ/mol for L-(+)-tartrate and 54.6 kJ/mol for D-(+)-malate. NAD was required as a cosubstrate, and optimal activity depended on the presence of both Mn2+ and NH4+ ions. The reactions followed Michaelis-Menten kinetics, and the apparent Km values of the individual reactants were determined to be: L-(+)-tartrate, 2.3 X 10(-3) M; NAD, 2.8 X 10(-4) M; and Mn2+, 1.6 X 10(-5) M with respect to L-(+)-tartrate; and D-(+)-malate, 1.7 X 10(-4) M; NAD, 1.3 X 10(-4); and Mn2+, 1.6 X 10(-5) M with respect to D-(+)-malate. Of a variety of compounds tested, only meso-tartrate, oxaloacetate, and dihydroxyfumarate were effective inhibitors. meso-Tartrate and oxaloacetate caused competitive inhibition, whereas dihydroxyfumarate caused noncompetitive inhibition. The Ki values determined for the inhibitors were, in the above sequence, 1.0, 0.014, and 0.06 mM with respect to L-(+)-tartrate and 0.28, 0.012, and 0.027 mM with respect to D-(+)-malate.

Malic enzyme from the rat mammary gland

"Malic" enzyme (EC 1.1.1.40) has been purified from rat mammary tissue and rat liver using a three stage procedure involving ammonium sulphate precipitation, affinity chromatography and ion exchange chromatography. The enzymes from the two tissues are similar in terms of their subunit and native molecular weights and kinetics with respect to both malate and NADP+. Antibodies to the two enzymes cross react with each enzyme. A single radial immunodiffusion assay showed a linear relationship between the activity and amount of enzyme protein in both mammary or liver preparations suggesting an immunochemical identity for the two enzymes. This assay was used to show that the greater than 5-fold change in activity which occurs during the lactation cycle is a consequence of differences in the amount of enzyme protein rather than any activation of a preformed enzyme.

Malolactic enzyme of Lactobacillus plantarum. Purification, properties, and distribution among bacteria

The malolactic enzyme of Lactobacillus plantarum was purified from 5.5 units/mg to a specific activity of 265 units/mg of protein. The enzyme has an isoelectric point of pH 4.4. The molecular weight is Mr = 140,000 as determined by gradient gel electrophoresis. The enzyme consists of two probably identical subunits (Mr = 70,000) that were observed after treatment with sodium dodecyl sulfate. Malolactic enzyme catalyzes the NAD- and manganese-dependent reaction L-malate leads to CO2 + L-lactate. Therefore, this enzyme can be distinguished from the well known malic enzymes (L-malate: NAD+ oxidoreductase, oxalacetate-decarboxylating EC 1.1.1.38 or 1.1.1.39). Malolactic enzyme is found in most lactic acid bacteria (Lactobacteriaceae); it has not been detected in other bacteria.

Light-stimulated synthesis of NADP malic enzyme in leaves of maize

Illumination of etiolated maize plants for 80 h brings about a 15-20-fold increase in activity of NADP malic enzyme (EC 1.1.1.40). Increases in NADP malic enzyme protein and in the level of translatable mRNA for this protein occur simultaneously with the activity increase. Radiolabeled amino acids are also incorporated into NADP malic enzyme during this time. These results are consistent with the conclusion that an increase in NADP malic enzyme activity during greening results from de novo synthesis of NADP malic enzyme protein. Polyadenylated RNA extracted from greening maize leaves directs the synthesis in vitro of a protein 12,000 daltons larger than NADP malic enzyme purified from corn leaves. This protein is a precursor of NADP malic enzyme because 1) both the precursor and mature NADP malic enzyme are immunoprecipitated by antibody made against NADP malic enzyme purified from corn leaves, 2) both NADP malic enzyme protein and the level of mRNA for the precursor increase during greening, and 3) peptide maps of the precursor and of mature NADP malic enzyme are very similar. Mature NADP malic enzyme and its precursor (synthesized in vitro) both migrate on sodium dodecyl sulfate-polyacrylamide gradient gels as doublet bands. Peptide analyses show all bands to be structurally related.

Large-scale purification of enzymes

Many standard procedures for the purification of proteins in the laboratory do not readily lend themselves to scaling up, whereas, on the other hand, some techniques relatively unsatisfactory in the laboratory are much more effective on a large scale. When producing gram or kilogram quantities of enzymes for use over an extended period, the storage properties and general tractability of the purified products become increasingly important. Hence enzymes from thermophilic sources frequently have advantages over those from mesophiles. The possible economic advantages of simultaneous large-scale multi-enzyme isolation over separate individual enzyme purifications are evaluated. Batchwise adsorption and elution from ion-exchange celluloses frequently replace traditional precipitation techniques in the early stages of a large-scale purification. Dialysis is replaced by concentration, dilution and reconcentration with the use of hollow-fibre ultrafiltration equipment. Antiphonally direct scaling-up of column chromatographic procedures is usually possible. Modifications to column geometry to maximize flow rates are often desirable but purification factors and recoveries comparable with those obtained on the laboratory scale can be achieved relatively easily. Classical affinity chromatographic techniques have not proved so amenable to large-scale work, mainly because of the enormous expense and rather short life of the matrices. However, the quasi-affinity chromatography afforded by the triazine dye conjugates has proved of great benefit. The materials are cheap to prepare. The coupling procedures are both simple and rapid and do not involve the use of noxious chemicals such as cyanogen bromide. Moreover the triazine linkage is more stable under a variety of conditions than the isourea formed in cyanogen bromide coupling. Considerable further exploitation of these versatile matrices is expected.