Peptide structures of pyruvate kinase isozymes: 2. Origins of types M1 and M2 isozymes suggested from species-variations in their peptide maps

Interfacial communications in recombinant rabbit kidney pyruvate kinase

Tissue-specific isozymes of pyruvate kinase are particularly attractive systems to elucidate the molecular mechanism(s) of conferring allostery. The muscle- and kidney-type isozymes are coded by the same gene. As a consequence of alternative message RNA splicing, the two primary sequences differ by a small number of residues. However, they exhibit very different regulatory behavior. In an effort to identify the roles of specific residues in conferring allostery, the gene encoding rabbit kidney-type pyruvate kinase was cloned and expressed in Escherichia coli. The primary structure of recombinant rabbit kidney-type pyruvate kinase (rRKPK) and recombinant rabbit muscle-type pyruvate kinase (rRMPK) differ at 22 positions, which are located in a region that forms important intersubunit contacts in the RMPK structure. Velocity sedimentation and analytical gel chromatographic studies show that rRKPK undergoes reversible dimer left and right arrow tetramer assembly with an equilibrium constant of 28 +/- 3 mL/mg. This subunit assembly process provides the opportunity to elucidate the role of this dimer interface in transmission of signal upon binding of substrates and allosteric effectors. The assembly to tetrameric rRKPK is favored by the binding of phosphoenolpyruvate (PEP), one of the two substrates, or fructose 1,6-bisphosphate (FBP), an activator. In contrast, the equilibrium is shifted toward dimeric rRKPK upon binding of adenosine diphosphate (ADP), the other substrate, or l-phenylalanine (Phe), the inhibitor. These observations provide significant new insights to the molecular mechanism of allosteric regulation in the pyruvate kinase system. First, all substrates and effectors communicate through this particular dimer-dimer interface. Second, the thermodynamic signatures of these communications are qualitatively different for the two substrates and between the activator, FBP, and inhibitor, Phe.

Phylogeny congruence analysis and isozyme classification: the pyruvate kinase system

As the isozymes of pyruvate kinase (PK) are best known in rats, the characteristics of the rat isozymes are generally used to classify the PK isozymes in other species. Given the discrepancies generated by this classification by analogy, we evaluated a classification using a phylogeny congruence analysis of the compositional relatedness of vertebrate PK's. While our phylogenetic analysis confirmed the well established separation of the L and R isozymes from the K and M isozymes, its power became most evident in the identification of non-orthologous (or variant) forms of PK. Our analysis emphasized the uniqueness of chicken liver PK which cannot be classified either as a K or an L isozyme, confirmed that tumors express a variety of forms of PK, and indicated that lungs systematically express PK's which are not orthologous with PK's from other tissues. The determination of orthology by the phylogeny congruence analysis assumes that the structural data from different sources are subject to similar methodological error. However, we cannot reject the possibility that an apparent lack of orthology be due to artifacts during purification and analysis.

Molecular and immunological characterization of plastid and cytosolic pyruvate kinase isozymes from castor-oil-plant endosperm and leaf

1. Monospecific antiserum was raised in rabbits to homogeneous cytosolic pyruvate kinase isolated from 5-day-old germinating endosperm of the castor oil plant, Ricinus communis. An earlier study demonstrated that the purified enzyme is putatively heterotetrameric, composed of two subunits which migrate as 57-kDa and 56-kDa proteins upon sodium dodecyl sulfate/polyacrylamide gel electrophoresis [Plaxton, W. C. (1988) Plant Physiol. (Bethesda) 86, 1065-1069]. Both proteins were detected on Western blots of extracts prepared under denaturing conditions from 4-8-day-old, but not 0-3-day-old, germinating-endosperm tissue. This suggests that both subunits exist in vivo, and that the large increase in pyruvate kinase activity which occurs around the fourth day of germination is due to an increase in pyruvate kinase concentration. 2. The cytosolic and plastidic pyruvate kinase isozymes (termed PKc and PKp, respectively) from castor-oil-plant developing endosperm and expanding leaf tissue were separated by anion-exchange chromatography on Q-Sepharose. The antigenic reaction of the partially purified enzyme preparations to rabbit polyclonal antibodies raised against homogeneous germinating-castor-bean PKc was tested by immunoprecipitation and Western blotting. Although developing-endosperm and leaf PKc appeared to be antigenically very similar to germinating-endosperm PKc, they differed from the heterotetrameric germinating-endosperm enzyme by being composed of a single type of subunit with a molecular mass of about 56 kDa. No cross-reactivity of the PKc antibodies was observed with either developing-endosperm or leaf PKp, nor with rabbit muscle or Bacillus stearothermophilus pyruvate kinase. Conversely, none of the castor-oil-plant pyruvate kinase preparations showed significant cross-reactivity with antibodies raised against purified yeast or rabbit muscle pyruvate kinases. 3. To investigate the structural relationship between the two germinating-endosperm-PKc subunits, each polypeptide was characterized by amino acid composition analysis and peptide mapping by CNBr fragmentation. The amino acid compositions and CNBr cleavage patterns of the two subunits were similar, but not identical, suggesting that these polypeptides are related, but distinct, proteins. Mild tryptic attack of native enzyme led to an approximate 6-kDa reduction in the apparent molecular mass of both subunits, further indicating sequence similarity between the two polypeptides. 4. Native molecular masses of the various castor-oil-plant pyruvate kinases were estimated by Superose-6 gel-filtration chromatography.(ABSTRACT TRUNCATED AT 400 WORDS)

Characterization of pyruvate kinase from human rhabdomyosarcoma in relation to immunohistochemical and morphological criteria

We have compared the pyruvate kinase (PK) isoenzyme pattern of three rhabdomyosarcomas with foetal skeletal muscle tissue of 19 and 23 weeks of gestation, together with adult muscle in relation to immunohistochemical and morphological criteria. In foetal tissue of 19 weeks of gestation a focal immunopositivity for desmin and myoglobin was observed, whereas in tissue of 23 weeks an overall positivity for these proteins was present. Two of the three neoplasms were poorly differentiated and of the alveolar subtype. They were desmin immunoreactive. Some large spindle-shaped cells expressed myoglobin. The third one was more differentiated in microscopic characteristics and all cells showed immunoreactivity for desmin and myoglobin. In the foetal tissues five forms of pyruvate kinase isoenzymes were present with K2M2 as the predominant form. In adult muscle tissue only M4 was present. The tumors were characterized by a profound shift to the K-type, whereas the M4-type was not expressed at all. A difference in isoenzyme composition of pyruvate kinase was found between the morphologically less differentiated tumors and the more differentiated tumor; in the latter more M-subunits were expressed.

Discrimination between neuronal and glial cell tumours by pyruvate kinase electrophoresis

Pyruvate kinase is a tetrameric enzyme, of which different isozymes are known (M, K and L). In normal human brain of adults mainly the M4 type is found with little or none of type K4 or the hybrid K3M. In gliomas of adults as well as in children a shift in the synthesis of isozymes of pyruvate kinase occurs from the M-towards the K-type. In these tumours the hybrid K2M2 is not expressed. In gliomas of children only a spur of K2M2 is found. There exists a peculiar difference in isozyme distribution of pyruvate kinase between gliomas on the one hand and neuro-, retino- and medulloblastomas on the other. In the latter group of tumours often the whole isozyme set is observed and in all cases the hybrids K2M2 and KM3 are found. These findings provide enzymological criteria for the discrimination of neuronal tumours from glial-cell tumours.

Pyruvate kinase and total protein are regulated differently during growth of P-815 mastocytoma cells

Total protein content of P-815 mastocytoma cells decreases and then increases in response to initiation of a new growth cycle. As the level increases, the rate of synthesis declines. Both events occur prior to any decrease in the rate of cellular proliferation. These temporal relationships indicate that the rate of protein synthesis reflects the intracellular concentration of protein rather than the cellular growth rate, as has been hypothesized. Pyruvate kinase protein metabolism differs from that of total protein in three ways: (a) accumulation does not stop, (b) the rate of synthesis does not decrease, and (c) only the rate of pyruvate kinase degradation is altered by a factor present in conditioned media. These observations suggest that there are specific mechanisms regulating pyruvate kinase at a post-transcriptional level.

Complete amino acid sequence of rat L-type pyruvate kinase deduced from the cDNA sequence

cDNA clones, containing the entire coding region of rat L-type pyruvate kinase, were isolated and their nucleotide sequences were determined by the dideoxy-chain-termination method. The predicted coding region, which spans 543 amino acids, established the complete amino acid sequence of the L-type isozyme of pyruvate kinase for the first time. The deduced amino acid sequence of the L type has one phosphorylation site in its amino terminus and shows about 68% and 48% homologies with M1-type pyruvate kinase of chicken and yeast pyruvate kinase respectively. Domain A exhibits higher homology than domains B and C. The residues in the active site of the L-type enzyme of rats, lying between domains B and A2, are rather different from those of the M1-type enzyme of chickens, but other residues constituting the active site are identical with those of the chicken M1 type except for one amino acid substitution.

Evolution of the functional properties of pyruvate kinase isozymes: pyruvate kinase L from Rana pipiens

The regulatory properties of type L pyruvate kinase from Rana pipiens are intermediate between those of the mammalian K and L isozymes. As with mammalian type L, the levels of the frog isozyme are affected by the animal's nutritional state. The mammalian and amphibian isozymes show similar sensitivities to fructose 1,6-bisphosphate activation and amino acid inhibition. By contrast, the frog L isozyme shares several properties of the K class: i.e. irreversible inactivation by oxidized glutathione and lack of response to a cyclic AMP stimulated phosphorylation. Furthermore, as for some mammalian K isozymes, frog type L shows a high PEP affinity and a low cooperativity of PEP binding. Insofar as the properties of this present day enzyme reflect those of its counterpart in the amphibian ancestor of higher vertebrates, our results suggest that at its first expression, the type L resembled the type K. Many important regulatory properties of the L isozyme, especially the sensitivity to phosphorylation, were acquired more recently perhaps in association with an increased importance of constant blood glucose.

Purification of pyruvate kinase isoenzymes type M1 and M2 from dog (Canis familiaris) and comparison of their properties with those from chicken and rat

Pyruvate kinase isoenzymes type M1 and M2 from dog muscle, lung and tumor have been isolated. The K0.5 for phosphoenol pyruvate have been determined to be 0.04 mM for dog muscle type M1, 0.24 mM for lung type M2 and 0.28 mM for tumor type M2 isoenzymes. The activator constant ka of L-serine is 240 nM from lung and 70 nM from tumor isoenzyme. Consistent with the assumption of a special form of pyruvate kinase M2 in dog tumor cells different isoelectric points and amino acid compositions have been found for the isoenzymes of lung and tumor.

Cell proliferation-associated expression of a recently evolved isozyme of triosephosphate isomerase

An electrophoretically unique, thermolabile isozyme of triosephosphate isomerase (TPI; EC 5.3.1.1) accounts for 10-30% of the enzymatic activity in a range of mitotically active human cells and tissues. This type 2 form (subunit) of human TPI appears in two isozymes, an anodally migrating, relative to the constitutive TPI-1/1 homodimer, TPI-2/2 homodimer and the TPI-1/2 heterodimer with an intermediate mobility. Human cell types expressing the induced isozyme, which is the product of the same structural locus as the constitutive isozyme, include mitogen-stimulated lymphocytes, virally transformed B-lymphoblastoid cells, leukemia-derived T-lymphoblastoid cells, HeLa cells, both normal and transformed fibroblasts, and placental tissue. Extracts of nondividing or terminally differentiated human cells/tissues, such as erythrocytes, striated muscle, peripheral lymphocytes, and platelets, contain high levels of the constitutive TPI-1/1 isozyme but little or undetectable levels of the TPI-1/2 or TPI-2/2 isozyme. The cell division-associated TPI-1/2 and -2/2 isozymes are distinct in electrophoretic mobility from the deamidated forms of the constitutive isozyme. Extracts of dividing gorilla fibroblasts display an isozyme pattern identical to that of proliferating human cells, but various proliferating cells derived from the African green monkey, rabbit, and chicken express only the constitutive isozyme. Thus, expression of the cell division-associated isozyme of TPI is restricted to the hominoids, suggesting a recently evolved modification mechanism which is specifically activated in proliferating cells.

The purification and kinetic characterization of eel white muscle pyruvate kinase

A stable, homogeneous preparation of pyruvate kinase from white muscle of the American eel, Anguilla rostrata with a specific activity of 350 units/mg has been obtained. The enzyme has a pH optimum in the range 6.3-6.5 and requires Mg2+ and K+ for maximum activity. Eel muscle pyruvate kinase exhibits slight co-operativity in the binding of the substrate phosphoenol-pyruvate. It is activated by fructose-1,6-bisphosphate in a pH dependent manner and is inhibited by both alanine and phenylalanine. These properties are very similar to the properties of the mammalian M2 isozyme.

The Pk-3 gene determines both the heart, M1, and the kidney, M2, pyruvate kinase isozymes in the mouse; and a simple electrophoretic method for separating phosphoglucomutase-3

We have found that in mice carrying Pk-3r, an allele leading to loss or activity of kidney pyruvate kinase, the activity of heart pyruvate kinase is also diminished. Electrophoretic studies on tissues from mice carrying Pk-3r and/or Pk-3b, an allele determining an electrophoretically detectable variant, show that Pk-3 affects the expression of both the heart, M1, and the kidney, M2, pyruvate kinase isozymes. These results, together with linkage data, indicate that both isozymes are determined by the same structural gene, Pk-3. We also report a simple method for separating phosphoglucomutase-3 (PGM-3) by electrophoresis on cellulose acetate plates.