Evolution of a gene. Multiple genes for LDH isozymes provide a model of the evolution of gene structure, function and regulation

Drosophila lactate dehydrogenase: developmental aspects

Partially purified lactate dehydrogenase (LDH) from third-instar larvae displays two bands (one major and one minor) on polyacrylamide gels. Analogous preparations from pupae and adults exhibit three LDH-staining bands (one major and two minor) in a similar pattern. The migration of the major band is similar for larvae, pupae, and adults, while the two minor LDH bands of pupae and adults migrate more slowly than the minor larval band. It has been shown that larval LDH incubated with beta-nicotinamide adenine dinucleotide exhibits two additional minor bands with an electrophoretic mobility similar to that of the minor bands of both pupae and adults. The intensity of the minor larval LDH band (exhibited also by untreated preparations) is drastically reduced. This fact indicates that the life-cycle stage-dependent LDH isozymic distribution is possibly due to a posttranslational effect(s). Highly purified LDH from larvae, pupae, or adults, obtained by an affinity chromatography procedure, displays just one dispersed band, located in the area between the band 5 and the band 6 exhibited by crude extract preparations. These data, in combination with the lack of difference in catalytic properties among enzymes from larvae, pupae, and adults, suggest that LDH synthesis is controlled by the same single structural gene at all developmental stages.

X-linked and autosomal inheritance patterns of homologous genes in two species of Tribolium

The tenebrionid beetles Tribolium castaneum and T. confusum are representative of two distinct species groups within their genus. It has been suggested [Smith, S.G. (1952). J. Morphol. 91:325] that the 8AA + neo-XY karyotype of T. confusum was derived from the ancestral 9AA + XY formula, still present in T. castaneum, via the fusion of one pair of autosomes with the X and Y chromosomes during the early divergence of the confusum and castaneum species groups. In the present paper, electrophoretic variation in malic enzyme and hexokinase-1, detected in laboratory strains in Tribolium, is described. Evidence is presented that the genes encoding variation in both enzymes are autosomal in T. castaneum but are X linked in T. confusum. These species-specific patterns of inheritance of homologous gene loci are consistent with the hypothesized karyotypic history of the genus.

Cardiac metabolism in the Myxinidae: physiological and phylogenetic considerations

Cardiac muscle hearts of Atlantic hagfish continuously function under hypoxic conditions that would lead to cardiac failure in most other vertebrates. Contractile performance of hagfish systemic hearts is resistant to anoxia and respiratory poisons but shows a significant decrement when carbohydrate catabolism is blocked by 0.5 mM iodoacetic acid. Enzyme activity profiles of hagfish ventricle reveal a robust capacity for glycolysis of carbohydrate in comparison to that for general aerobic metabolism and catabolism of alternate metabolic fuels. Isolated working hagfish ventricles preferentially oxidize radiolabeled glucose even when fatty acid fuels are present in the incubation medium. Work output of the isolated ventricular preparation is maintained only in the presence of exogenous glucose. The results indicate that energy metabolism of the hagfish myocardium is predominantly carbohydrate-based and that energy demand of the tissue can be sustained by anaerobic glycolysis during extended periods of extreme hypoxia. Cardiac metabolism of this primitive species is compared with that of hearts from higher vertebrates and an evolutionary hypothesis relating cardiac workload to preferred metabolic fuel is discussed.

Adaptative features of ectothermic enzymes--IV. Studies on malate dehydrogenase of Astyanax fasciatus (Characidae) from Lobo Reservoir (Såo Carlos, Såo Paulo, Brasil)

1. Skeletal muscle and heart supernatant malate dehydrogenase (s-MDH) from a subtropical fish, Astyanax fasciatus consists of three electrophoretically anodal bands. Each band is a dimer (AA, AB and BB) and two loci are active. 2. In A. fasciatus tissue extracts, A and B subunits are present at differing quantitative levels and their activities are almost season-independent. However, the relative activity of each homodimer in relation to total s-MDH estimated by densitometry of gels or of each homodimer purified by chromatography varies with temperature. The more anodic homodimer is thermolabile and the less anodic one is thermostable. 3. The pH optimum of s-MDH is 7.5, of AA is 6.5 and of BB is 7.8. 4. The BB isozyme is more sensitive to high concentrations of substrate and has a Km temperature-independent. The AA isozyme is not inhibited by high concentrations of oxaloacetate and shows a Km temperature-dependent with a fourteenfold increase between 20 degrees and 40 degrees C.

Drosophila lactate dehydrogenase: molecular and genetic aspects

(LDH) obtained from larvae of Drosophila melanogaster was purified to homogeneity by affinity chromatography on oxamate-Sepharose. The purification procedure is simple to operate and gives a homogeneous preparation in a good yield (34.86%) after only two steps. Utilizing the homogeneous LDH preparation, an attempt was made to characterize the LDH molecule. Thus, it was found that the N-terminal amino acid is isoleucine, and the enzyme is tetrameric and composed of four identical subunits of apparent molecular weight 38,000, suggesting that it is controlled by a single gene. Homogeneous LDH preparations exhibit one band on neutral acrylamide gels when the substrate is either DL-lactic acid or L-(+)-lactate. The optimum temperature is 45 degrees C for the purified enzyme and 40 degrees C for the crude homogenate. The Km values for pyruvate and NADH are 0.154 and 0.027 mM, respectively, while the Km values for lactate and NAD are 29.4 and 1.33 mM, respectively. A discontinuity in the Ea slope was observed at a transition temperature of 30 degrees C. The Ea value between 20 and 30 degrees C was calculated as 12.06 kcal/mol, while between 30 and 45 degrees C the Ea value was 4.01 kcal/mol. This evidence, together with other observations reported in the literature, suggests that the LDHs of invertebrates and vertebrates have arisen by divergent evolution from a common ancestral gene.

Lactate dehydrogenase of Xenopus laevis laevis and Xenopus borealis depends on a multiple gene system

Lactate dehydrogenase isozymes have been reinvestigated in Xenopus laevis laevis and Xenopus borealis. High resolution zymograms of various organs demonstrate that in both species the LDH isozymes are governed basically by a three-gene system: Ldh-a coding for positively charged polypeptide, and Ldh-b and Ldh-c for negatively charged polypeptides (at pH 8.9). These three LDH subunits when assembled in tetramers show differential sensitivity to heat inactivation; the C4 homotetramer is the most labile isozyme. Xenopus is thus similar to Osteichthyes, birds, and mammals that also have a three-gene system for LDH. With respect to tissue specific isozyme expression, Xenopus resembles the more primitive families of bony fish. Superimposed on this three-gene system is a probable gene duplication for both LDH-a and Ldh-b. Heterotetrameric isozymes are formed between the various subunits leading to multibanded zymograms with a total of at least 21 distinct zones of LDH activity. The expression of genes is tissue specific not only for the basic genes, but also for their presumed duplicates. Since both species of Xenopus are ancient tetraploids, duplication of Ldh genes is not surprising.

Evolution of human Y-chromosome DNA

We have used human male-specific 3.4 kb Hae III restriction endonuclease fragments to explore the evolutionary history of man's Y-chromosome. We have identified four sets of reiterated sequences on the basis of their relative sequence homology with autosomal DNA. The sequences account for approximately 40% of the human Y-chromosome, are interspersed within the same 3.4 kb Hae III fragments, are heterogeneous and contain all reiterated DNA previously demonstrated to be specific for the Y-chromosome (it-Y DNA). Y-specific 3.4 kb Hae III sequences do not reassociate with either human female or ape DNA at standard reassociation criteria. However, approximately half of it-Y DNA (cross reacting it-Y) reassociates with both human female and ape DNA at reduced reassociation criteria. The remaining half (Y-specific it-Y) retains its specificity for the human Y-chromosome. These two sets of it-Y DNA have distinct reiteration frequencies and thermal stabilities with their Y-chromosome homologs. Non-Y-specific 3.4 kb Hae III sequences reassociate with both human female and ape DNA at standard reassociation criteria. The abundance of these non-Y-specific sequences decreases as a function of their evolutionary distance for man. One subset of non-Y-specific 3.4 kb Hae III sequences forms stable duplexes with human Y-chromosome DNA and with human and ape autosomal DNA. No detectable base-mismatch occurs among these homologs suggesting complete conservation of these sequences during primate evolution. The second subset of Non-Y-specific Hae III sequences form stable duplexes with human Y-chromosome DNA but highly mismatched duplexes with human and ape autosomal DNA. The finding that homologs of 3.4 kb Hae III sequences are not found within the Y-chromosome of apes but are only present in autosomes suggests that 3.4 kb Hae III sequences are largely autosomal in origin. Since autosomal homologs of most 3.4 kb Hae III-sequences exhibit a greater degree of divergence that those localized to the Y-chromosome, their evolutionary history seems to be chromosome-dependent. Our findings are not easily correlated with the comparative morphology of primate Y-chromosomes and suggest that sequence rearrangement has been a major event in the evolution of the human Y-chromosome. The significance of the specific interspersion of four sets of reiterated sequences, with distinct evolutionary histories, within a repeating unit specific to the human Y-chromosome is not clear. The apparent conservation of at least some of these reiterated sequences suggests they may be of functional importance.

An esterase duplication in Drosophila: differences in expression of duplicate loci within and among related species

An esterase duplication is described in the sibling species pair Drosophila mojavensis and Drosophila arizonensis. We present evidence for two separate structural loci mapping at a distance of less than 0.16 recombination units from each other. Alleles at the two loci have the same substrate specificities and form small amounts of interlocus heterodimers. One locus (Est-5) is functioning throughout the insect's life cycle and appears at high concentrations in the hemolymph and the fat body. Its duplicate (Est-4) functions only during the late larval stage and is concentrated mainly in the carcass. No null alleles at either locus were observed in population surveys. An examination of 12 other species from the repleta group, to which D. mojavensis and D. arizonesis belong, suggests that Est-5 is universally present, but the activity levels of Est-4 vary among species and may be totally absent in some species. Variation in the level of Est-4 activity does not closely follow the phylogenetic relationship.

Soluble peptidase isozymes of the Japanese Medaka (Oryzias latipes): tissue distributions and substrate specificities

Peptidases catalyze the hydrolysis of di- and tripeptidases to their constituent amino acids. Five isozymes (PEP A, B, C, D, and S) were shown to be the products of independent genetic loci by several criteria including distinct adult tissue and substrate specificities, non-cross-reacting immunochemical properties, and independent genetic variation at three of the loci. Four of the peptidases had at least one substrate against which they contributed over 95% of the activity. These substrates were used for isozyme-specific assays. In adult tissues, three of the peptidases had higher activities in liver and intestine than in other tissues (PEP A, B, and S). PEP C had a 10-fold higher specific activity in brain than in other tissues.

Identification of lactate dehydrogenase-X translated in vitro from mouse testicular poly A-containing mRNA

1. The LDH-X polypeptide was specifically immunoprecipitated from the cell-free translation products of poly A-containing mRNA from mouse testes, and it represents 1-2% of the total proteins synethesized in vitro. 2. The in-vitro synthesized LDH-X polypeptide appears to have the same mol. wt of 36,000 as mouse authentic LDH-X and, thus, any presequence of LDH-X must be very short, if present at all. 3. The LDH-X was not found in the mouse liver mRNA translation products immunoprecipitated by anti-LDH-X antibodies.

Adaptative features of ectothermic enzymes--I. Temperature effects on the malate dehydrogenase from a temperate fish Leiostomus xanthurus

1. Following electrophoresis the s-MDH activity of Leiostomus xanthurus and many other species of fish and amphibian appears in three sharp, equally-spaced, anodal bands. Each band is a dimer (AA, AB and BB) and two loci are active. 2. In Leiostomus tissue extracts A and B subunits are present are differing quantitative levels and their activities can be modified by changes in environment temperature. 3. Thermostability and thermal dependency tests show that, similar to what occurs during acclimatization, the AA isozyme is more stable to heat than is the BB isozyme. The BB isozyme is activated by low temperatures and is rapidly inactivated by high temperatures. 4. Extracts from a variety of fishes, amphibians, reptiles and birds suggest that when only one or two s-MDH bands are present, they behave as dose the AA homodimer in Leiostomus Xanthurus, i.e., are stable at elevated temperatures.

2,4,5-T effects on cardiac and serum lactic dehydrogenase (LDH) and creatine kinase (CK) isozymes. I. Maternal enzyme activities and isozyme profiles

Pregnant mice were exposed to 100 mg/kg 2,4,5-T, IG, on gestation days 6 through 17, and sacrificed on postpartum day 1 or 21. Toxicologic evaluation showed no changes in body weight, heart weight, heart to body weight ratio, or cardiac supernate protein between corn oil control and 2,4,5-T treated mice on days 1 or 21 postpartum (pp). There were no effects of 2,4,5-T treatment on the total LDH enzyme activity of cardiac supernate on day 1 or 21pp. Serum LDH total activity was depressed on day 1pp and comparable to control values on day 21pp. Cardiac CK total activity was elevated on day 1pp, but not on day 21pp. Serum CK total activity on day 1 was comparable to control values; however, on day 21, a significant decrease in activity was observed. Cardiac LDH and CK isozyme profiles were normal on days 1 and 21pp. The serum LDH isozyme profile was normal at both times. The serum CK isozyme profile on Day 1 was markedly altered by athe appearance of two aberrant isozyme bands while on day 21, there was a profile shift with an increase in the BB band and a compensatory decrease in the MM band. These changes in creatine kinase suggest metabolic or pathologic changes in the cardiac muscle.

Aldehyde oxidases of Drosophila: contributions of several enzymes to observed activity patterns

At least four enzymes contribute to histochemically, electrophoretically, or spectrophotometrically detectable aldehyde oxidase (AO) activity in Drosophila melanogaster. The one we designate AO-1 contributes the majority of activity measured in extracts of whole flies. Pyridoxal oxidase (PO) is also a broad range AO. It is prominent only in midgut and Malpighian tubules, where it apparently accounts for a substantial fraction of total AO activity. The tissue distributions of these enzymes are clearly disparate despite close linkage of their structural loci and parallel dependence on the mal, lxd, and cin loci. A similarly related enzyme, xanthine dehydrogenase (XDH), is detected as an AO only in electrophoretic gels. A fourth broad range AO, not dependent on mal, lxd, and cin, is confined to the ejaculatory bulb. A similar array of AO isozymes is present in phylogenetically distant Drosophila species.

Biochemical properties of duplicated isozymes of phosphoglucose isomerase in the plant Clarkia xantiana

The structural gene locus specifying subunits of cytoplasmic isoenzymes of phosphoglucose isomerase (PGI) is present in duplicate in many diploid species of Clarkia (Onagraceae), a genus of annual plants native to California. We studied the kinetic properties and molecular weights of a large number of genetically defined and highly purified PGIs in C. xantiana, a number of species with the duplication, as a means of examining the biochemical consequences of the evolution of a new gene locus. This species is primarily outcrossing, but also includes several previously described predominantly self-pollinating populations. Both cytoplasmic PGI loci in the outcrossing populations are polymorphic and their enzyme products are readily separated by electrophoresis. The PGIs from the outcrossing populations were rated by electrophoresis. The PGIs from the outcrossing populations were generally closely similar in molecular weight, pH optimum, heat sensitivity, energy activation, and apparent Km (fructose-6-phosphate). The PGI loci in the selfing populations are monomorphic and specify enzymes having identical electrophoretic mobilities to those coded by the most frequent alleles of the outcrosser. The PGI isozymes in the selfers differed fivefold in Km, suggesting that they have a very different catalytic effectiveness. The high Km of the PGI-3A' isozyme (1.1mM) was anomalous among the PGIs examined and would likely be disadvantageous in a species which lacked other more normally functioning PGIs. But in the cytoplasm of the selfing plants, it is present with other PGIs that have low Km values. The PGI-3A' enzyme is a good candidate for a gene product coded by a "forbidden" mutation that could not have been established in the absence of the duplication. The rationale for this suggestion is described and it is also pointed out that the divergence of duplicated genes is influenced by many factors such as the breeding system and other population factors as well as the effect of particular mutations.

Evolution of patterns of gene expression in hawaiian picture-winged Drosophila

The tissue and stage specificity of expression of five enzymes was examined by electrophoretic analysis of relative enzyme levels in extracts of 13 larval and adult tissues in 27 species of Hawaiian picture-winged Drosophila. The developmentally regulated patterns of enzyme expression thus characterized were compared to a modal standard phenotype. About 30% of the pattern features analyzed differed significantly from the standard in one or more species. Many of these regulatory differences are essentially qualitative, with tissue specific differences in enzyme activity in excess of 100 fold for some species pairs. The adaptive significance of these pattern differences in unknown, but the results provide strong direct evidence for rapid evolution of new patterns of gene regulation in this group of organisms.

Properties of arginase from liver of Macaca fascicularis; comparison of normals with red blood cell arginase deficient monkeys

Deficiency of arginase (E.C. 3.5.3.1), the fifth enzyme of the urea cycle, was found in the red blood cells (RBCs) of Macaca fascicularis monkeys (less than 0.2 micromol arginine cleaved/g Hb/min; normal equals 49.2). Liver biopsies were obtained from two of these monkeys and from one monkey with normal levels of RBC arginase activity. Arginase from both groups of animals required Mn2+ for maximal enzyme activity and demonstrated a pH optimum of 10.2 in vitro. The activity of arginase in the livers of all three monkeys was 1.1 millimol arginine cleaved per g protein per min. The apparent Km for arginine of arginase in the livers of the RBC-deficient monkeys was 7.4 and 5.9 mM and in the normal monkey was 6.9 mM. Similar patterns of heat denaturation was seen at 69 C without Mn2+ present and 79 C in the presence of 20mM Mn2+. No difference in mobility on either RBC-deficient or normal monkeys was found. In addition, liver arginase from all three monkeys reacted similarly with anti-human liver arginase antibody. Liver arginases in RBC-deficient and normal monkeys were identical by ten criteria. These studies do not distinguish among several hypotheses for the genetic determination of arginase in different organs of this species and of man.

Malate dehydrogenase isozymes in the longnose dace, Rhinichthys cataractae

The interspecies homology of dace supernatant (A2,AB,B2) and mitochondrial (C2) malate dehydrogenase isozymes has been established through cell fractionation and tissue distribution studies. Isolated supernatant malate dehydrogenase (s-MDH) isozymes show significant differences in Michaelis constants for oxaloacetate and in pH optima. Shifts in s-MDH isozyme pH optima with temperature may result in immediate compensation for increase in ectotherm body pH with decrease in temperature, but duplicate s-MDH isozymes are probably maintained through selection for tissue specific regulation of metabolism.

Lactate dehydrogenases of Atlantic hagfish: physiological and evolutionary implications of a primitive heart isozyme

Isozymes of lactate dehydrogenase from heart and muscle of Atlantic hagfish show less functional divergence than those from other fishes and higher vertebrates. The enzyme from hagfish heart (B4) displays a higher Michaelis constant for pyruvate and lower substrate inhibition at moderate pyruvate concentrations than heart isozymes from other species. These properties support the hypothesis that the ancestral vertebrate lactate dehydrogenase was a muscle (A4)-type enzyme and also suggest a role for the B4 enzyme in the unusual physiology of hagfish cardiac tissue which functions under sustained hypoxic conditions.

Linkage conservation of homologous esterase loci in fish (Cyprinodontoidei: Poeciliidae)

Homologies among esterase isozymes in fish in the poeciliid genera Poeciliopsis and Xiphophorus are proposed. Esterase homologies are based on their tissue distributions and inhibition and substrate properties. The five esterases include two carboxylesterases, one eserine sulfate-sensitive esterase, and two esterases resistant to inhibition, one of which reacts only with acetate esters. Linkage studies in Poeciliopsis monacha indicate that the loci encoding the two carboxylesterases are linked to each other and to the locus for eye-specific lactate dehydrogenase. Comparisons of the linking reported here with earlier studies in Xiphophorus suggest that there is a large region of linkage homology in the genetic maps of Poeciliopsis and Xiphophorus.

Pyruvate kinases of salmon: purification and comparison with the isozymes from birds and mammals

Pyruvate kinase occurs as two major forms in coho salmon; the type M isozyme occurs primarily in muscle and heart, but type K has a more generalized tissue distribution, in parallel with the type K isozyme in other vertebrate systems. In order to assess the evolutionary relationships among the fish, avian, and mammalian isozymes of pyruvate kinase, we have purified the two isozymes from fish, have examined some of their physical properties, and have studied their immunological relationships to the avian and mammalian isozymes. Salmon type K is at least partially inactivated by antibody to bivine type L pyruvate kinase as well as by antibodies produced against chicken, bovine, and salmon type M isozymes. Salmon type M pyruvate kinase, on the other hand, is not significantly corss-reactive with the bovine type L isozyme, but is at least partially inactivated by antibodies produced against bovine or chicken type M isozymes. Mammalian type L pyruvate kinase is immunologically distinct from either mammalian type K or type M, but salmon type K has some structural features in common with all three mammalian isozymes. Thus, salmon fish type K pyruvate kinase could be similar to a primordial form that was antecedent to the three major differentiated isozymes of higher vertebrates.

Structural relatedness of mouse lactate dehydrogenase isozymes, A4 (muscle), B4 (heart), and C4 (testis)

Three homotetrameric lactate dehydrogenase isozymes, LDH-M(A4), LDH-H(B4), and LDH-X(C4), from DBA/2J mice have been purified by affinity chromatography. The amino acid compositions of the subunits A,B, and C, based on a molecular weight of 36,000, have been determined. The compositional relatedness of these isozymes indicates that subunits A (muscle) and B (heart) are more closely related to each other than to subunit C (testis). Tryptic peptide maps and amino acid compositions of some active site peptides apear to confirm the compositional relatedness among these isozymes. The sequence of the loop region of mouse C subunit seems to be markedly different from all known A and B sequences, and the structural and functional implications are discussed.

Epigenetic formation of lactate dehydrogenase isozymes in the house mouse, Mus musculus

The origin of mouse lactate dehydrogenase (LDH) sub-bands was investigated by using our miniaturized polyacrylamide gel electrophoretic apparatus. Mouse LDH isozymes are generated by combinations of three types of A subunit, the primary type and two epigenetically modified forms. These are designated A1, A2, and A3 in the order of their electrophoretic mobilities towards the anode. The A1 subunit arises from the covalent binding of molecules of glutathione through disulfide bonds to the original subunit, A3. The A2 subunit arises from the covalent binding of molecules of cysteine through disulfide bonds to the A3 subunit. All isozymes can be explained as tetramers composed of the three kinds of A subunit (A1, A2, or A3) in combination with B subunits to yield a total of 35 isozymes. The kinetic properties of these sub-bands were also examined. There was no difference between A24 and A34 in the Km for pyruvate and for lactate. Thermostability at 56 degrees C was greater for A34 than for A24. The activities of tetramers at the electrophoretic position of A3B1 and A4 in extracts containing all five isozymes were increased by treatment of the extracts with high concentrations of reduced glutathione or cysteine with the concomitant disappearance or decrease in activity of tetramers at the position of B4 and A3B1. These results suggest that, in the presence of reduced glutathione or cysteine, LDH isozymes containing the B subunit are first dissociated and then the A subunits are preferentaially recombined.

Evolution of the differential regulation of duplicate genes after polyploidization

In the 50 million years since the polyploidization event that gave rise to the catostomid family of fishes the duplicate genes encoding isozymes have undergone different fates. Ample opportunity has been available for regulatory evolution of these duplicate genes. Approximately half the duplicate genes have lost their expressions during this time. Of the duplicate genes remaining, the majority have diverged to different extents in their expression within and among adult tissues. The pattern of divergence of duplicate gene expression is consistent with the accumulation of mutations at regulatory genes. The absence of a correlation of extent of divergence of gene expression with the level of genetic variability for isozymes at these loci is consistent with the view that the rates of regulatory gene and structural gene evolution are uncoupled. The magnitude of divergence of duplicate gene expressions varies among tissues, enzymes, and species. Little correlation was found with the extent of divergence of duplicate gene expression within a species and its degree of morphological "conservatism", although species pairs which are increasingly taxonomically distant are less likely to share specific patterns of differential gene expression. Probable phylogenetic times of origin of several patterns of differential gene expression have been proposed. Some patterns of differential gene expression have evolved in recent evolutionary times and are specific to one or a few species, whereas at least one pattern of differential gene expression is present in nearly all species and probably arose soon after the polyploidization event. Multilocus isozymes, formed by polyploidization, provide a useful model system for studying the forces responsible for the maintenance of duplicate genes and the evolution of these once identical genes to new spatially and temporally specific patterns of regulation.

Developmental changes in the pyruvate kinase isozymes of coho salmon

Pyruvate kinase exists as two major isozymes in coho salmon. As in mammals and birds, one form is present in the early embryo and maintains a wide tissue distribution in adults. This salmonid type K shows anodal migration during electrophoresis at pH 7.5. The appearence of functional musculature in the developing embryos. In adult animals this second form is the only pyruvate kinase in muscle. Brain, kidney, liver and gill contain primarily the type K pyruvate kinase while heart contains both major forms along with three intermediate forms which presumably constitute a hybrid set. Since there is no additional isozyme restricted to gluconeogenic tissues, we conclude that a type L isozyme has not developed in these animals. The two major isozymes are immunologically distincy. Both forms are dubject to fructose 1,6-bisphosphate activation of phosphoenolpyruvate binding, but the magnitude of the effect is small. The affinities for phosphoenolpyruvate are similar, but salmon type K has hyperbolic saturation curves with this substrate and type M has sigmoidal saturation curves. While the immunological data indicates considerable divergence in structure, the kinetic parameters of the two forms have remained relatively similar.

Alcohol dehydrogenase activity in diploid and autotetraploid Phlox

The effect of polyploidy on the activity of alcohol dehydrogenase was examined in a series of diploid and synthetic autotetraploid Phlox drummondii. In most cases autotetraploids had about twice as much activity as the corresponding diploids, in two cases autotetraploids had about 1.5 times more activity, and in one wild seed pair the activity of the tetraploid was somewhat lower.

Evolution of acid phosphatase-1 in the genus Drosophilia. Immunological studies

The enzyme acid phosphatase-1 was partially purified from 10 Drosophila species. Four antisera were produced and the ten enzymes were reacted against each serum. The method used to quantitate the reactions involved the electrophoretic separation of antigen-antibody complexes from uncomplexed enzyme, followed by densitometry of the free enzyme. Immunological distances were used to obtain correlation coefficients for all pairwise combinations of the 10 species. From these correlation coefficients, a dendrogram was constructed which is very similar to one diagramming the presumed phylogenetic relationships of the ten species. In addition, the data indicate acid phosphatase-1 has evolved at different rates in different lineages within the genus. A preliminary estimate of the unit evolutionary period for this enzyme is 3.25 million years. The method of determining immunological distances which was used in this study is compared to the method of microcomplement fixation in the Discussion.

Evolution of isozyme loci and their differential tissue expression. Creatine kinase as a model system

The phylogeny of the creatine kinase (CK, EC 2.7.3.2) isozyme loci and their differential tissue expressions were determined for representatives of 65 families of vertebrates, with emphasis on the fishes. The transition from the single creatine kinase locus, characteristic of certain echinoderms, to the two creatine kinase loci which are orthologous to those present in all vertebrates, occurred early in the chordate line. The majority of pre-teleostean fishes possesses only these two CK loci (A and C). These loci are relatively generalized in their tissue expressions which are variable among species of primitive fishes. The third and fourth creatine kinase loci (B and D) arose separately in the ancestors of the bony fishes and appear to be the result of regional genome duplications. Concomitant with the increase in the number of isozyme loci has been an increase in the specificity of their tissue expression. In the advanced teleost fishes the four CK loci are differentially expressed in a characteristic manner. The A2 isozyme predominates in skeletal muscle, the B2 isozyme in eye and brain, the C2 isozyme in stomach muscle, and the D2 isozyme is found exclusively in testis. We propose a phylogeny of the creatine kinase genes in the lower chordates based on the time of appearance of new CK loci, the sequence in which the loci achieve a tissue restricted expression, and the immunochemical relatedness of the orthologous and paralogous gene products.

Genetic and molecular analysis of nonrandom dimer assembly of the creatine kinase isozymes of fishes

Species within many families of actinopterygian bony fishes (class Osteichthyes) have a two-banded allelic isozyme phenotype in individuals heterozygous at the creatine kinase A locus. This two-banded pattern is formed by the presence of the two homodimeric isozymes and the absence of the expected heterodimer. Sharks and amphibians have retained the ability to form all three allelic isozymes in individuals which are heterozygous. Reversible denaturation procedures were able to assemble the different allelic CK-A subunits within a species to form CK-A2 heterodimers. Furthermore, heterodimers were formed from different CK-A subunits from highly divergent species after this in vitro molecular hybridization process. It is concluded from these studies that the polypeptide-binding sites of creatine kinase are structurally conservative in most fishes and that the absence of a heterodimer in heterozygous individuals is not due to a structural incompatibility between the different A subunit types or to an instability of the heterodimer during electrophoresis. A temporal and/or spatial isolation of allelic CK-A subunit synthesis and assembly, within differentiated skeletal muscle, appears to have evolved in the actinopterygian bony fishes.

Identification and linkage relationships of three hexokinase genes in Aedes aegypti

Four regions of hexokinase activity are detected by starch gel electrophoresis of adult Aedes aegypti. Three of the regions, Hk-2, Hk-3, and Hk-4, are produced by three tightly linked loci, located on the third chromosome 7.25 map units from the locus fuzzy. The three loci show developmental differences as well as differences in substrate specificity.