Increase in photosynthesis of maize hybrids (<Emphasis Type="Italic">Zea mays</Emphasis> L.) at suboptimal temperature (15 °C) by selection of parental lines on the basis of chlorophyll <Emphasis Type="Italic">a</Emphasis> fluorescence measurements

We tested the usefulness of chlorophyll a fluorescence quenching analysis for the selection of maize parental inbred lines able to produce F₁ hybrids with a high CO₂ assimilation rate during growth at suboptimal temperature. Fifty inbred lines, grown at 15 °C, showed at 6 °C a broad genetic variability regarding the quantum yield of photosynthetic electron transport (_PS2). A decrease of _PS2 in sensitive lines was caused more by reduction of the efficiency of excitation energy capture by open photosystem 2 (PS2) reaction centres (F_v'/F_m') than by a drop in photochemical quenching (q_P). Selected inbred lines with the highest (H) and the lowest (L) values of _PS2 were used for separate crossings in a diallelic arrangement. Twenty-one of H×H hybrids and 21 of the L×L hybrids were grown at 15 °C. The H×H hybrids showed at suboptimal temperature a significantly higher transport of photosynthetic electrons than the L×L hybrids at lower (400) as well as at higher [800 mol(photon) m^–2 s^–1] irradiance. The mean net photosynthetic rate (P _N) in H×H and L×L hybrids amounted to 8.4 and 5.8 (second leaf) and 8.5 and 7.6 mol(CO₂) m^–2 s^–1 (third leaf), respectively. Among the best 20 hybrids with regard to P _N (values larger than the average) of second leaves, as many as 15 were derived from H lines (75 % of hybrids), whereas among the best 21 hybrids with regard to P _N of the third leaves, 16 were derived from H lines (76 % of hybrids). The intensive P _N of H×H hybrids was most often accompanied by less water lost via transpiration in relation to photosynthesis than in the hybrids of L lines. Hence an analysis of chlorophyll a fluorescence quenching enables the selection of inbred lines, which can produce hybrids with improved CO₂ fixation and with efficient water management during growth at suboptimal temperature.     

Human β-glucuronidase: Assignment of the structural gene to chromosome 7 using somatic cell hybrids

-Glucuronidase (GUS) has become an important enzyme model for the genetic study of molecular disease, enzyme realization, and therapy, and for the biogenesis and function of the lysosome and lysosomal enzymes. The genetics of human -glucuronidase was investigated utilizing 188 primary man-mouse and man-Chinese hamster somatic cell hybrids segregating human chromosomes. Cell hybrids were derived from 16 different fusion experiments involving cells from ten different and unrelated individuals and six different rodent cell lines. The genetic relationship of GUS to 28 enzyme markers representing 19 linkage groups was determined, and chromosome studies on selected cell hybrids were performed. The evidence indicates that the -glucuronidase gene is assigned to chromosome 7 in man. Comparative linkage data in man and mouse indicate that the structural gene GUS is located in a region on chromosome 7 that has remained conserved during evolution. Involvement of other chromosomes whose genes may be important in the final expression of GUS was not observed. A tetrameric structure of human -glucuronidase was demonstrated by the formation of three heteropolymers migrating between the human and mouse molecular forms in chromosome 7 positive cell hybrids. Linkage of GUS to other lysosomal enzyme genes was investigated. -Hexosaminidase HEX _B) was assigned to chromosome 5; acid phosphatase₂ (ACP ₂) and esterase A₄ (ES-A ₄) were assigned to chromosome 11; HEX _A was not linked to GUS; and -galactosidase (-GAL) was localized on the X chromosome. These assignments are consistent with previous reports. Evidence was not obtained for a cluster of lysosomal enzyme structural genes. In demonstrating that GUS was not assigned to chromosome 9 utilizing an X/9 translocation segregating in cell hybrids, the gene coding for human adenylate kinase₁ was confirmed to be located on chromosome 9.Supported by NIH Grants HD 05196, GM 20454, and GM 06321, by NSF Grant BMS 73-07072, and by HEW Maternal and Child Health Service, Project 417.     

cGMP-stimulated protein kinase phosphorylates pyruvate kinase in an anoxia-tolerant marine mollusc

Summary A cystosolic protein kinase that phosphorylates pyruvate kinase (PK) in vitro has been identified in crude homogenates of heart, radular retractor, and foot muscle from the anoxia-tolerant marine whelk Busycon canaliculatum. Protein kinase action was measured by following changes in PK kinetic parameters: phosphorylated PK has a higher K _m value for phosphoenolpyruvate and a lower I₅₀ value for l-alanine. The crude protein kinase readily phosphorylated PK in a Mg²⁺-and ATP-dependent manner in the absence of any added effector. This activity was not affected by the addition of either cAMP (a stimulator of protein kinase A) or Ca²⁺ plus phorbol 12-myristate 13-acetate (stimulators of protein kinase C) to the incubation medium. Addition of cGMP to the homogenate, however, increased the rate of PK phosphorylation giving a 3–4-fold increase in the rate of change in PK kinetic parameters that was readily apparent after 5h. Complete time-courses of changes in PK kinetic parameters in the presence and absence of cGMP showed that cGMP increased the rate, but not the final extent, of PK phosphorylation. These results indicate that PK inactivation by enzyme phosphorylation in response to anoxia in whelk tissues may be mediated by a cyclic GMP stimulated protein kinase in response to changing levels of cGMP. This conclusion was further supported by data indicating that the total activity of protein kinase was the same in both anoxic and aerobic animals, and that the total PK phosphatase activity was also constant. Changes in PK phosphorylation during anoxia are not, therefore, the result of changes in the total amount of protein kinase or phosphatase.Abbreviations cAMP adenosine 3:5-monophosphate - cGMP guanosine 3:5-monophosphate - PK pyruvate kinase - PMA phorbol 12-myristate, 13-acetate - PEP phosphoenolpyruvate - K _m Michaelis constant - I ₅₀ inhibitor concentration that reduces enzyme activity by 50%     

Regulatory role of δ-aminolevulic acid dehydratase in the dimorphic fungus Mucor rouxii

• 1.1. With the aim of finding a possible relationship between the known dimorphism phenomenon existing in the fungus Mucor rouxii and the biosynthesis of respiratory pigments, the activity of aminolevulic acid synthetase (ALA-S) and ALA-dehydratase (ALA-D) was studied in crude extracts and in 15,000 g supernatants of both mycelium and yeast-like cells.
• 2.2. The activity of ALA-S was unusually high (3 nmol ALA/hr/mg protein) compared with that reported for other tissues and did not vary with the fungus morphology.
• 3.3. Instead, ALA-D specific activity was found to be 16.5 nmol PBG/hr/mg protein in mycelium extracts, that is 7-fold greater than that measured in the yeast-like morphology (2.6 nmol PBG/hr/mg protein).
• 4.4. It was of importance to determine the activity levels of ALA-D along with the morphogenic transition from yeast to mycelium. It was observed that the greatest change and enhancing of specific activity occurred 2 hr before the emergence of the germ tubes and was held constant up to the complete development of mycelium.
• 5.5. Both hyphae formation and enhancement of ALA-D activity were diminished when cAMP was added to the culture shifted from the anaerobic atmosphere to air.
• 6.6. These findings and preliminary studies on the characterization of M. rouxii ALA-D indicate that this enzyme plays a regulatory role in porphyrin biosynthesis in this fungus as well as a key function in the characteristic morphogenic transition.

     

The effect of population structure on the relationship between heterosis and heterozygosity at marker loci

The relationship between heterozygosity at neutral marker loci and heterosis of F₁ hybrids is investigated using a theoretical model. Results emphasize that linkage disequilibrium between the markers and the loci implicated in heterosis [quantitative trait loci (QTLs) that exhibit dominance effects] is a necessary condition to finding a correlation ( _mh ) between heterozygosity at marker loci and the heterosis. The effect of population structure, in which the parental inbred lines of the hybrids belong to different heterotic groups, is considered. _mh is investigated for: (1) hybrids between lines that belong to the same heterotic group (within-group hybrids); (2) hybrids between lines that belong to different groups (between-group hybrids); and (3) all hybrids, both within and between-groups. Within a group, significant values of ( _mh ) may arise because of linkage disequilibrium generated by drift. At the between-group level, no correlation is expected since link-age disequilibrium should differ randomly from one group to the other, which is consistent with recent experimental results. Possible ways to achieve prediction of the heterosis in this situation are discussed. When all hybrids are considered simultaneously, divergence of allelic frequencies among groups for the markers and the QTLs produces a correlation between heterosis and heterozygosity at marker loci. This correlation increases with the number of markers that are considered.     

Kinetics of protein aggregation. Quantitative estimation of the chaperone-like activity in test-systems based on suppression of protein aggregation

The experimental data on the kinetics of irreversible aggregation of proteins caused by exposure to elevated temperatures or the action of denaturing agents (guanidine hydrochloride, urea) have been analyzed. It was shown that the terminal phase of aggregation followed, as a rule, first order kinetics. For the kinetic curves registered by an increase in the apparent absorbance (A) in time (t) the methods of estimation of the corresponding kinetic parameters A _lim and k _I (A _lim is the limiting value of A at t and k _I is the rate constant of the first order) have been proposed. Cases are revealed when the reaction rate constant k _I calculated from the kinetic curve of aggregation of the enzymes coincides with the rate constant for enzyme inactivation. Such a situation is interpreted as a case when the rate of aggregation is limited by the stage of denaturation of the enzyme. A conclusion has been made that, in order to establish the mechanism of protein aggregation, the kinetic investigations of aggregation should be carried out over a wide range of protein concentrations. The refolding experiments after denaturation of proteins by guanidine hydrochloride or urea have been also analyzed. It was shown that aggregation accompanying refolding follows first order kinetics at the final phase of the process. The model of protein refolding explaining such a kinetic regularity has been proposed. When aggregation of protein substrate follows first order kinetics, parameters A _lim and k _I may be used for the quantitative characterization of the chaperone-like activity in the test-systems based on suppression of protein aggregation.     

Characterization of the monophenolase activity of tyrosinase on betaxanthins: the tyramine-betaxanthin/dopamine-betaxanthin pair

Tyrosinase or polyphenol oxidase (EC 1.14.18.1) is the key enzyme responsible for melanin biosynthesis and for the enzymatic browning of fruits and vegetables. Although the function of tyrosinase in the secondary metabolism of plants remains unclear, it has been proposed that the enzyme plays a role in the betalain biosynthetic pathway. Betalains are an important class of water-soluble pigments, characteristic of plants belonging to the order Caryophyllales. In the present work, the betaxanthins tyramine-betaxanthin (miraxanthin III) and dopamine-betaxanthin (miraxanthin V) are reported as new natural substrates for tyrosinase. The result of the diphenolase activity of the enzyme on dopamine-betaxanthin was a series of products identified by HPLC and ESI-MS as quinone-derivatives. Data indicate that dopamine-betaxanthin-quinone is obtained and evolves to more stable species by intramolecular cyclization. The kinetic parameters evaluated for the diphenolase activity were V_m=74.4 M min^–1, K_m=94.7 M. Monophenolase activity on tyramine-betaxanthin yielded the same compounds in the absence of a reducing agent, but when ascorbic acid was present enzymatic conversion to dopamine-betaxanthin could be found. For the first time, kinetic characterization of the monophenolase activity of tyrosinase on betaxanthins is provided (V_m=10.4 M min^–1 and K_m=126.9 M) and a lag period is described and analyzed according to the mechanism of action of the enzyme. The high affinity shown by tyrosinase for these substrates may be indicative of a previously unconsidered physiological role in betalain metabolism. A possible mechanism for the formation of 2-descarboxy-betacyanins from tyramine-betaxanthin by tyrosinase is also discussed.     

Chloroplast DNA codes for the ribulose diphosphate carboxylase catalytic site on fraction I proteins of Nicotiana species

Summary The specific activity of ribulose diphosphate carboxylase and the K _m for ribulose 1–5 diphosphate of Fraction I protein isolated from N. gossei was significantly higher than enzyme from six other species of Nicotiana which were closely similar to each other. In several interspecific, reciprocal F₁ hybrids, the higher N. gossei activity was present only when N. gossei was the female parent. Consequently, the maternal mode of inheritance indicates chloroplast DNA to contain information which regulates the conformation of the catalytic site on the enzyme. Previous results had shown this DNA to code for the primary structure of the large subunit. In hybrids where N. gossei was the female parent, the specific enzyme activity was intermediate between N. gossei itself and the other parent because of formation of isozymes of Fraction I protein which were demonstrated by tryptic peptide fingerprints of the small subunits of Fraction I protein from N. gossei, N. excelsior, and reciprocal hybrids. Peptides characteristic of the enzyme from each parent were found in both hybrids. Previous results had demonstrated that nuclear genes contain the code for the small subunit. In the hybrid where N. gossei is the female parent, the reduction in specific enzyme activity from that of N. gossei itself is evidently the result of N. excelsior type small subunits modifying the catalytic site on the N. gossei type of large subunits. A hybrid protein of lesser activity is produced which dilutes the higher activity of the N. gossei type protein.     

Analysis of essential leucine residue for catalytic activity of novel thermostable chitosanase by site-directed mutagenesis

Bacterial chitosanases share weak amino acid sequence similarities at certain regions of each enzyme. These regions have been assumed to be important for catalytic activities of the enzyme. To verify this assumption, the functional importance of the conserved region in a novel thermostable chitosanase (TCH-2) from Bacillus coagulans CK108 was investigated. Each of the conserved amino acid residues (Leu64, Glu80, Glu94, Asp98, and Gly108) was changed to aspartate and glutamine or asparagine and glutamate by site-directed mutagenesis, respectively. Kinetic parameters for colloidal chitosan hydrolysis were determined with wild-type and 10 mutant chitosanases. The Leu64 Arg and Leu64 Gln mutations were essentially inactive and kinetic parameters such as V _max and k _cat were approximately 1/10⁷ of those of the wild-type enzyme. The Asp98 Asn mutation did not affect the K _m value significantly, but decreased k _cat to 15% of that of wild-type chitosanase. On the other hand, the Asp98 srarr; Glu mutation affected neither K _m nor k _cat. The observation that approximately 15% of activity remained after the substitution of Asp98 by Asn indicated that the carboxyl side chain of Asp98 is not absolutely required for catalytic activity. These results indicate that the Leu64 residue is directly involved in the catalytic activity of TCH-2.     

The chemical mechanism of action of glucose oxidase from Aspergillus niger

Glucose oxidase from Aspergillus niger (EC 1.1.3.4) is able to catalyze the oxidation of -D-glucose with p-benzoquinone, methyl-1,4-benzoquinone, 1,2-naphthoquinone, 1,2-naphthoquinone-4-sulfonic acid, potassium ferricyanide, phenazine methosulfate, and 2,6-dichloroindophenol. In this work, the steady-state kinetic parameters, V ₁/K _B , for reactions of these substrates were collected from pH 2.5–8. Further, the molecular models of the enzyme's active site were constructed for the free enzyme in the oxidized state, the complex of -D-glucose with the oxidized enzyme, the complex of reduced enzyme with methyl-1,4-benzoquinone, the reduced enzyme plus 1,2-naphthoquinone-4-sulfonic acid, oxidized enzyme plus reduced 1,2-naphthoquinone-4-sulfonic acid (hydroquinone anion), and oxidized enzyme plus fully reduced 1,2-naphthoquinone-4-sulfonic acid.Combining the steady-state kinetic and structural data, it was concluded that Glu412 bound to His559, in the active site of enzyme, modulates powerfully its catalytic activity by affecting all the rate constants in the reductive and the oxidative half-reaction of the catalytic cycle. His516 is the catalytic base in the oxidative and the reductive part of the catalytic cycle. It was estimated that the pK _a of Glu412 (bound to His559) in the free reduced enzyme is 3.4, and the pK _a of His516 in the free reduced enzyme is 6.9.     

The association between malathion resistance and acetylcholinesterase in Drosophila melanogaster

The relationship between the 50% survival time for flies feeding on a malathion-containing medium and the activity of acetylcholinesterase (AChE) was determined for 15 isofemale lines of Drosophila melanogaster. A significant correlation was found (r=0.28, P<0.05), with more resistant lines tending to have a lower level of AChE activity. An association between AChE and malathion resistance was also observed in a selection experiment. The AChE activity decreased in two of two populations selected for malathion resistance. AChE from these populations was altered in kinetic parameters (measured in crude head extracts) and electrophoretic mobility. Although the resistant AChE had a lower activity (V _m) on either a per milligram protein or a per individual basis, its apparent K _m for acetylthiocholine was lower than that of susceptible AChE. Recombination mapping of both low activity and fast electrophoretic mobility localized these traits to the region of the structural locus (Ace) on the third chromosome. The AChE activity of flies heterozygous for a variety of Ace lesions (kindly provided by Dr. W. M. Gelbart) was consistent with this location. The changes in AChE were suggested to have been caused by selection of alleles at the Ace locus.This work was supported by NSERC Grants A5857, G0183, and A0629.     

Purification and properties of the catalytic domain of the thermostable pullulanase type II from Thermococcus hydrothermalis

A pullulanase type II was produced in Escherichia coli using the relevant gene from Thermococcus hydrothermalis. This protein was purified and its pullulanolytic and amylolytic activities were characterised. The optimum temperature and Ca²⁺ concentration for each activity were identical (105 °C and 0.09 mM), whereas the optimum pH (pH_pullulan 5.75, pH_amylose 5) and the influence of Ca²⁺ ions on the kinetic parameters were different. Further analyses revealed that this enzyme exhibits an endo-processive-like action and specifically cleaves -1,6 bonds in pullulan.     

Allosterische Regulation der Aktivität der Glutamatdehydrogenase aus Erbsenkeimlingen durch das Substrat α-Ketoglutarsäure

Summary Several investigations on the properties of glutamate dehydrogenase from plant sources indicate that the enzymatic activity (reductive amination) follows a Michaelis-Menten-type kinetic when velocity is plotted versus rising concentrations of the substrate -ketoglutarate. In the course of our investigations on the effect of SO₂ on pea plant enzymes we found that SO ₄ ^2- , added as (NH₄)₂SO₄ to the assay system, causes this type of activity response because of its ability to function as an activator. When (NH₄)₂SO₄ is replaced by NH₄Cl in the in vitro system however, activity response is sigmoidal. Addition of competitive inhibitor to the latter system again gives rise to a sigmoidal kinetic with reduced initial velocities. Identical kinetic behaviour is observed when either 120 fold enriched enzyme from shoots or highly purified glutamate dehydrogenase from pea roots is used, a fact which justifies the assumption that the enzyme from pea plants belongs to the MIC-type of regulatory proteins (modulator independent cooperativity). The activity response caused by other effectors, especially purine nucleotides, is discussed with regard to the above findings.     

Effect of some metals and related metal-orgaic compounds on ALA-dehydratase activity of corn

Summary The activity of ALA-dehydratase from corn seedlings is affected by Mn⁺⁺, Fe⁺⁺, Pb⁺⁺, Cu⁺⁺, Zn⁺⁺ and Sn⁺⁴ ions, in vivo Mn⁺⁺ and Fe⁺⁺ are ativators while Pb⁺⁺ and Sn⁺⁴ are inhibitors; in vitro Cu⁺⁺ and Zn⁺⁺ are inhibitors. The kinetic parameters (V_max and K_M) support the hypothesis that Mn, Fe, Sn and Pb ions act on the biosynthesis of the enzyme and Zn and Cu ions on the enzyme-substrate affinity. Some related metal-organic compounds interrere in vivo on the ALA-dehydratase activity modifying the kinetic parameters, therefore the enzyme biogenesis and/or enzyme-sustrat affinity are affected.     

Kinetic characterization of GABA-transaminase from cultured neurons and astrocytes

The enzymatic mechanism and the kinetic parameters of GABA-transaminase extracted from cultured mouse cerebral cortex neurons and astrocytes were studied. Neuronal as well as astrocytic GABA-transaminase obeyed a bi bi ping-pong reaction mechanism. The estimated K_m-values for -ketoglutarate and GABA were significantly lower for astroglial GABA-transaminase compared to the neuronal enzyme suggesting a possible existence of cell specific isozymes of GABA-transaminase. The observed enzymatic mechanism and the magnitude of the estimated kinetic parameters imply that GABA-transaminase synthesized in the two types of cultured neural cells is mechanistically and kinetically equivalent to the enzyme synthesized in the brainin vivo.     

Cyclic nucleotide metabolism during amphibian forelimb regeneration

Summary Concentrations of the cyclic nucleotides in regenerating limb tissues change in a manner which suggests that they might mediate neural or endocrine influences upon specific developmental events. Since modulation of the role of cAMP within this process can be achieved through cAMP phosphodiesterase, enzymatic activity, relative intracellular distribution, and the kinetic parameters of this enzyme were examined at several stages of limb regeneration in adultNotophthalmus viridescens. Both forms of the phosphodiesterase displayed decreased activity about the time of bud formation. Total phosphodiesterase activity was reduced between 66% and 85% (as compared to intact limbs) between wound healing and palette stages. Relative intracellular distribution (soluble vs. particulate), however, remained essentially constant, 93%–98% soluble for the highK _m form and 61%–71% soluble for the lowK _m form of the enzyme, throughout this process. The apparentK _m of the highK _m form increased more than 2-fold during wound healing then fell to approximately 10% (0.7–1.1 M) of the value of intact limbs (8.3 M) during dedifferentiation and bud formation. A return to pre-amputational levels was subsequently achieved. In contrast, the apparentK _m of the lowK _m form increased (from 0.064 to 0.86 M) during dedifferentiation and began decreasing thereafter. These results are consistent with the hypothesis that one or more mechanisms are operating to modify either the quantity, activity, or physical characteristics of the cAMP phosphodiesterases and that such changes are instrumental in regulating endogenous concentrations of cAMP in limb tissues during regeneration.     

Human δ-aminolevulinate dehydratase: chromosomal localization to 9q34 by in situ hybridization

Summary The structural gene for human -aminolevulinate dehydratase (ALA-D) has been localized to chromosomal region 9q34 by in situ hybridization using a [¹²⁵I]-labeled human -aminolevulinate dehydratase cDNA. Of the 150 silver grains analyzed, 25% were localized to chromosome 9q, while 12% and 8% were on chromosomes 1p and 13q, respectively. The single chromosomal region q34 had over 90% of the total grains observed on chromosome 9. In contrast, the grains on chromosomes 1p and 13q were dispersed, consistent with the absence of any human ALD-D pseudogenes. Southern blot analysis of somatic cell hybrids informative for ALA-D (Wang et al. 1985) also was consistent and supported the finding of only one locus for this heme biosynthetic enzyme.     

The effects of ‘gibberellin-insensitive’ dwarfing alleles in wheat on grain weight and protein content

Summary Three series of near-isogenic wheat lines differing in dwarfing alleles, in the varietal backgrounds of Maris Huntsman, Maris Widgeon and Bersee, and the F₂ grain on intravarietal F₁ hybrids, produced with a chemical hybridising agent, were examined for grain size and protein content. Individual F₂ grains from Rht1/rht, Rht2/rht and Rht3/rht F₁ spikes were classified for Rht genotype by assaying embryo half grains in a gibberellic acid seedling response test, while the remaining half was used for protein determination. Mean grain weight and protein percentage were lower in all homozygous isogenic lines and the Rht/rht F₁ hybrids than in the respective tall lines, in an allele dose-dependent manner. In all the hybrids, the Rht genotype of individual F₂ grains, which segregated within the spikes of F₁ plants, had no significant effects on grain weight or protein. Consequently, the pleiotropic effects of the Rht alleles on these yield and quality components must be attributed to their presence in maternal plant tissues rather than in the endosperm or embryo tissues of individual grains.     

Genetic studies of self-fertility in rye (Secale cereale L.). 1. The identification of genotypes of self-fertile lines for the Sf alleles of self-incompatibility genes

Segregation for self-fertility has been studied in progenies from the crosses of self-sterile (SS) plants with interline hybrids obtained by a diallel scheme of pollinations between seven self-fertile (SF) lines (nos. 2–8) and with F₁ (SS plant x SF line) hybrids. All the offspring families from the SS plant x F₁ (SS plant x SF line) crosses demonstrated a 1SF1SS segregation. The crosses of SS plants with some interline hybrids gave only self-fertile plants, whereas the crosses with other interline hybrids gave a segregation of 3SF:1SS expected in the case of digenic segregation. The data obtained permitted us to identify three different S loci (S1, S2, S5) and to estimate the genotypes of self-fertile lines for their Sf alleles: lines 5, 6, 7 and 8 are S1f/S1f S2n/S2n S5m/S5m, line 4 is S1n/S1n S2f/S2f S5m/S5m, and lines 2 and 3 are S1n/S1n S2m/S2m S5f/S5f(Sn, Sm designate active alleles of the incompatibility genes). The identification of the particular S gene which is presented by the Sf allele in each line has been made on the basis of our data concerning the linkage of the Sf mutation with isozyme markers of particular rye chromosomes, which is reported in an accompanying paper.     

Malic enzyme of Chromatium vinosum

Malic enzyme of the phototrophic bacterium Chromatium vinosum strain D that lacks malate dehydrogenase was partially purified yielding a specific activity of 55 units/mg protein. The constitutive enzyme with a molecular weight of 110,000 and a pH optimum of 8.0 was absolutely dependent on the presence of a monovalent cation (NH ₄ ⁺ , K⁺, Cs⁺, or Rb⁺) as well as a divalent cation (Mn²⁺, or Mg²⁺). The enzyme was inhibited by oxaloacetate, glyoxylate, and NADPH. The K _0.5 value for L-malate and the inhibition constants for oxaloacetate and glyoxylate are dependent on the concentration of the monovalent cation, whereas the K _m value for NADP (18 M) and the K ₁ value for NADPH (42 M) are independent. Throughout all kinetic measurements hyperbolic saturation curves and linear double reciprocal plots were obtained.Abbreviations OAA oxaloacetate - OD optical density