Phylogenetic distribution in the genus Mus of t-complex-specific DNA and protein markers: inferences on the origin of t-haplotypes

We have examined the phylogenetic distribution of two t-specific markers among representatives of various taxa belonging to the genus Mus. The centromeric TCP-1a marker (a testicular protein variant specific for all t-haplotypes so far studied) has also been apparently detected in several non-t representatives of the Mus IVA, Mus IVB, and probably M. cervicolor species. By contrast, a t-specific restriction- fragment-length polymorphism allele (RFLP) of the telomeric alpha- globin pseudogene DNA marker alpha-psi-4 was found only in animals belonging to the M. musculus-complex species either bearing genuine t- haplotypes or, like the M. m. bactrianus specimen studied here, likely to do so. This t-specific alpha-psi-4 RFLP allele was found to be as divergent from the RFLP alleles of the latter, non-t, taxonomical groups as it is from Mus 4A, Mus 4B, or M. spretus ones. These results suggest the presence of t-haplotypes and of t-specific markers in populations other than those belonging to the M. m. domesticus and M. m. musculus subspecies, implying a possible origin for t-haplotypes prior to the radiation of the most recent offshoot of the Mus genus (i.e., the spretus/domesticus divergence), some 1-3 Myr ago.      

Biochemical properties of alcohol dehydrogenase from Drosophila lebanonensis.

Purified Drosophila lebanonensis alcohol dehydrogenase (Adh) revealed one enzymically active zone in starch gel electrophoresis at pH 8.5. This zone was located on the cathode side of the origin. Incubation of D. lebanonensis Adh with NAD+ and acetone altered the electrophoretic pattern to more anodal migrating zones. D. lebanonensis Adh has an Mr of 56,000, a subunit of Mr of 28 000 and is a dimer with two active sites per enzyme molecule. This agrees with a polypeptide chain of 247 residues. Metal analysis by plasma emission spectroscopy indicated that this insect alcohol dehydrogenase is not a metalloenzyme. In studies of the substrate specificity and stereospecificity, D. lebanonensis Adh was more active with secondary than with primary alcohols. Both alkyl groups in the secondary alcohols interacted hydrophobically with the alcohol binding region of the active site. The catalytic centre activity for propan-2-ol was 7.4 s-1 and the maximum velocity of most secondary alcohols was approximately the same and indicative of rate-limiting enzyme-coenzyme dissociation. For primary alcohols the maximum velocity varied and was much lower than for secondary alcohols. The catalytic centre activity for ethanol was 2.4 s-1. With [2H6]ethanol a primary kinetic 2H isotope effect of 2.8 indicated that the interconversion of the ternary complexes was rate-limiting. Pyrazole was an ethanol-competitive inhibitor of the enzyme. The difference spectra of the enzyme-NAD+-pyrazole complex gave an absorption peak at 305 nm with epsilon 305 14.5 X 10(3) M-1 X cm-1. Concentrations and amounts of active enzyme can thus be determined. A kinetic rate assay to determine the concentration of enzyme active sites is also presented. This has been developed from active site concentrations established by titration at 305 nm of the enzyme and pyrazole with NAD+. In contrast with the amino acid composition, which indicated that D. lebanonensis Adh and the D. melanogaster alleloenzymes were not closely related, the enzymological studies showed that their active sites were similar although differing markedly from those of zinc alcohol dehydrogenases.     

The contractile basis of amoeboid movement: V. The control of gelation, solation, and contraction in extracts from dictyostelium discoideum

Motile extracts have been prepared from Dictyostelium discoideum by homogenization and differential centrifugation at 4 degrees C in a stabilization solution (60). These extracts gelled on warming to 25 degrees Celsius and contracted in response to micromolar Ca++ or a pH in excess of 7.0. Optimal gelation occurred in a solution containing 2.5 mM ethylene glycol-bis (β-aminoethyl ether)N,N,N',N'-tetraacetate (EGTA), 2.5 mM piperazine-N-N'-bis [2-ethane sulfonic acid] (PIPES), 1 mM MgC1(2), 1 mM ATP, and 20 mM KCI at ph 7.0 (relaxation solution), while micromolar levels of Ca++ inhibited gelation. Conditions that solated the gel elicited contraction of extracts containing myosin. This was true regardless of whether chemical (micromolar Ca++, pH >7.0, cytochalasin B, elevated concentrations of KCI, MgC1(2), and sucrose) or physical (pressure, mechanical stress, and cold) means were used to induce solation. Myosin was definitely required for contraction. During Ca++-or pH-elicited contraction: (a) actin, myosin, and a 95,000-dalton polypeptide were concentrated in the contracted extract; (b) the gelation activity was recovered in the material sqeezed out the contracting extract;(c) electron microscopy demonstrated that the number of free, recognizable F-actin filaments increased; (d) the actomyosin MgATPase activity was stimulated by 4- to 10-fold. In the absense of myosin the Dictyostelium extract did not contract, while gelation proceeded normally. During solation of the gel in the absense of myosin: (a) electron microscopy demonstrated that the number of free, recognizable F- actin filaments increased; (b) solation-dependent contraction of the extract and the Ca++-stimulated MgATPase activity were reconstituted by adding puried Dictyostelium myosin. Actin purified from the Dictyostelium extract did not gel (at 2 mg/ml), while low concentrations of actin (0.7-2 mg/ml) that contained several contaminating components underwent rapid Ca++ regulated gelation. These results indicated : (a) gelation in Dictyostelium extracts involves a specific Ca++-sensitive interaction between actin and several other components; (b) myosin is an absolute requirement for contraction of the extract; (c) actin-myosin interactions capable of producing force for movement are prevented in the gel, while solation of the gel by either physical or chemical means results in the release of F-actin capable of interaction with myosin and subsequent contraction. The effectiveness of physical agents in producting contraction suggests that the regulation of contraction by the gel is structural in nature.     

Metal-directed affinity labeling of zinc(II), cobalt(II) and cadmium(II) horse liver alcohol dehydrogenases

The active site metal in horse liver alcohol dehydrogenase has been studied by metal-directed affinity labeling of the native zinc(II) enzyme and that substituted with cobalt(II) or cadmium(II). Reversible binding of bromoimidazolyl propionic acid to the cobalt enzyme blueshifts the visible absorption band originating from the catalytic cobalt atom at 655 to 630 nm. Binding of imidazole to the cobalt(II) enzyme redshifts the 655 nm band to 667 nm. Addition of bromoimidazolyl propionic acid blueshifts this 667 nm band back to 630 nm. This proves direct binding of the label to the active site metal in competition with imidazole. The affinity of the label for the reversible binding site in the three enzymes follows the order Zn ? Cd ? Co. After reversible complex formation, bromoimidazolyl propionic acid alkylates cysteine-46, one of the protein ligands to the active site metal. The nucleophilic reactivity of this metal-mercaptide bond in each reversible complex follows the order Co ? Zn ? Cd.     

The kinetic mechanism of sheep liver sorbitol dehydrogenase.

The relations between the kinetic parameters for both sorbitol oxidation and fructose reduction by sheep liver sorbitol dehydrogenase show that a Theorell-Chance compulsory order mechanism operates from pH 7.4 to 9.9. This is supported by many parallels with the kinetics of horse liver alcohol dehydrogenase, which operates by this classical mechanism. An isotope-exchange study using D-(2H8)sorbitol confirmed the existence of ternary complexes and that, under maximum velocity conditions, their interconversion is not rate-determining. Substrate inhibition at high concentrations of D-sorbitol or D-fructose confirmed rate-determining enzyme--coenzyme product dissociation, slowed by the existence of more stable abortive ternary enzyme-coenzyme product complexes with substrate. The effect of the inhibitor/activator 2,2,2-tribromoethanol showed the existence of enzyme-NAD-CBr3CH2OH complexes inhibiting the first phase of reaction and enzyme-NADH-CBr3CH2OH complexes dissociating more rapidly than the usual rate-determining enzyme-NADH coenzyme product dissociation in the final phase. Inhibition studies with dithiothreitol also confirmed an ordered binding of coenzymes and second substrates to sorbitol dehydrogenase. Neither D-sorbitol nor D-fructose had any effect on enzyme inactivation by the affinity labelling reagent DL-2-bromo-3-(5-imidazolyl)propionic acid, thus giving no evidence for their existence as binary enzyme-substrate complexes. Several alternative polyol substrates for sorbitol dehydrogenase gave the same maximum velocity as sorbitol. This indicated a common rate-limiting binary enzyme-NADH product dissociation and a similarity of mechanism. An enzyme assay for pH 7.0 and 9.9 is given which enables the concentration of sorbitol dehydrogenase to be determined from initial rate measurements of enzyme activity.     

The reactivity of affinity labels: A kinetic study of the reaction of alkyl halides with thiolate anions—a model reaction for protein alkylation

Factors have been investigated which govern the electrophilic reactivity of alkyl halides with thiolate anions in aqueous solution. In the series of alkyl halides studied, some are potential metal-directed affinity labels, while others are frequently used in protein modification. Previous data on the kinetics of this type of alkylation are compared with the present results. The influence of electronic, polar, and steric factors on alkyl halide reactivity is seen. The following order of reactivity for alkyl halides bearing different α substituents was observed: RCH₂CH(X)COOCH₃ > RCH₂CH(X)CONH₂ > RCH₂CH(X)COOH > RCH₂CH₂X > RCH₂CH(X)CH₂OH. The metal-directed affinity labels are imidazole derivatives, some of which have substituents in their imidazole ring. The effect of the imidazole ring and of ring substitution on reactivity is seen. The nucleophilic reactivity of thiols is highly pH dependent since the thiolate anion (RS^?) is the reactive species, but only minor differences emerged between different free thiolates.     

Phosphate binding to liver alcohol dehydrogenase studied by the rate of alkylation with affinity labels

In this work we report that phosphate anions interact with the anion binding site of alcohol dehydrogenase from horse liver. In protection experiments against the two affinity labels, iodoacetic acid and bromo-imidazolylpropionic acid, the dissociation constant for the enzyme-phosphate complex at pH 7.0 is, based on total phosphate, found to be 20 +/- 5 mM. The 1,4-piperazinediethanesulfonate anion has a lower affinity for the anion binding site, the dissociation at pH 7.0 being 130 +/- 20 mM. The anion-independent dissociation constants for the reversible enzyme-affinity label complexes are at pH 7.0, 1.35 +/- 0.2 mM for iodoacetic acid and 0.39 +/- 0.05 mM for bromo-imidazolylpropionic acid. These findings have important implications with respect to past and future work on this well known enzyme.     

Roles of creatine in the regulation of cardiac protein synthesis

The observation that increased muscular activity leads to muscle hypertrophy is well known, but identification of the biochemical and physiological mechanisms by which this occurs remains an important problem. Experiments have been described (5, 6) which suggest that creatine, an end product of contraction, is involved in the control of contractile protein synthesis in differentiating skeletal muscle cells and may be the chemical signal coupling increased muscular activity and the increased muscular mass. During contraction, the creatine concentration in muscle transiently increases as creatine phosphate is hydrolyzed to regenerate ATP. In isometric contraction in skeletal muscle for example, Edwards and colleagues (3) have found that nearly all of the creatine phosphate is hydrolyzed. In this case, the creatine concentration is increased about twofold, and it is this transient change in creatine concentration which is postulated to lead to increased contractile protein synthesis. If creatine is found in several intracellular compartments, as suggested by Lee and Vissher (7), local changes in concentration may be greater then twofold. A specific effect on contractile protein synthesis seems reasonable in light of the work of Rabinowitz (13) and of Page et al. (11), among others, showing disproportionate accumulation of myofibrillar and mitochondrial proteins in response to work-induced hypertrophy and thyroxin-stimulated growth. Previous experiments (5, 6) have shown that skeletal muscles cells which have differentiated in vitro or in vivo synthesize myosin heavy-chain and actin, the major myofibrillar polypeptides, faster when supplied creatine in vitro. The stimulation is specific for contractile protein synthesis since neither the rate of myosin turnover nor the rates of synthesis of noncontractile protein and DNA are affected by creatine. The experiments reported in this communication were undertaken to test whether creatine selectively stimulates contractile protein synthesis in heart as it does in skeletal muscle.     

Transbilayer movement of Glc-P-dolichol and its function as a glucosyl donor: protein-mediated transport of a water-soluble analog into sealed ER vesicles from pig brain

The results described in the accompanying article support the model in which glucosylphosphoryldolichol (Glc-P-Dol) is synthesized on the cytoplasmic face of the ER, and functions as a glucosyl donor for three Glc-P-Dol:Glc0-2Man9-GlcNAc2-P-P-Dol glucosyltransferases (GlcTases) in the lumenal compartment. In this study, the enzymatic synthesis and structural characterization by NMR and electrospray-ionization tandem mass spectrometry of a series of water-soluble beta-Glc-P-Dol analogs containing 2-4 isoprene units with either the cis - or trans - stereoconfiguration in the beta-position are described. The water- soluble analogs were (1) used to examine the stereospecificity of the Glc-P-Dol:Glc0-2Man9GlcNAc2-P-P-Dol glucosyltransferases (GlcTases) and (2) tested as potential substrates for a membrane protein(s) mediating the transbilayer movement of Glc-P-Dol in sealed ER vesicles from rat liver and pig brain. The Glc-P-Dol-mediated GlcTases in pig brain microsomes utilized [3H]Glc-labeled Glc-P-Dol10, Glc-P-(omega, c )Dol15, Glc-P(omega, t,t )Dol20, and Glc-P-(omega, t,c )Dol20as glucosyl donors with [3H]Glc3Man9GlcNAc2-P-P-Dol the major product labeled in vitro. A preference was exhibited for C15-20 substrates containing an internal cis -isoprene unit in the beta-position. In addition, the water-soluble analog, Glc-P-Dol10, was shown to enter the lumenal compartment of sealed microsomal vesicles from rat liver and pig brain via a protein-mediated transport system enriched in the ER. The properties of the ER transport system have been characterized. Glc- P-Dol10was not transported into or adsorbed by synthetic PC-liposomes or bovine erythrocytes. The results of these studies indicate that (1) the internal cis -isoprene units are important for the utilization of Glc-P-Dol as a glucosyl donor and (2) the transport of the water- soluble analog may provide an experimental approach to assay the hypothetical "flippase" proposed to mediate the transbilayer movement of Glc-P-Dol from the cytoplasmic face of the ER to the lumenal monolayer.      

Microengineered systems with iPSC-derived cardiac and hepatic cells to evaluate drug adverse effects

Hepatic and cardiac drug adverse effects are among the leading causes of attrition in drug development programs, in part due to predictive failures of current animal or in vitro models. Hepatocytes and cardiomyocytes differentiated from human induced pluripotent stem cells (iPSCs) hold promise for predicting clinical drug effects, given their human-specific properties and their ability to harbor genetically determined characteristics that underlie inter-individual variations in drug response. Currently, the fetal-like properties and heterogeneity of hepatocytes and cardiomyocytes differentiated from iPSCs make them physiologically different from their counterparts isolated from primary tissues and limit their use for predicting clinical drug effects. To address this hurdle, there have been ongoing advances in differentiation and maturation protocols to improve the quality and use of iPSC-differentiated lineages. Among these are in vitro hepatic and cardiac cellular microsystems that can further enhance the physiology of cultured cells, can be used to better predict drug adverse effects, and investigate drug metabolism, pharmacokinetics, and pharmacodynamics to facilitate successful drug development. In this article, we discuss how cellular microsystems can establish microenvironments for these applications and propose how they could be used for potentially controlling the differentiation of hepatocytes or cardiomyocytes. The physiological relevance of cells is enhanced in cellular microsystems by simulating properties of tissue microenvironments, such as structural dimensionality, media flow, microfluidic control of media composition, and co-cultures with interacting cell types. Recent studies demonstrated that these properties also affect iPSC differentiations and we further elaborate on how they could control differentiation efficiency in microengineered devices. In summary, we describe recent advances in the field of cellular microsystems that can control the differentiation and maturation of hepatocytes and cardiomyocytes for drug evaluation. We also propose how future research with iPSCs within engineered microenvironments could enable their differentiation for scalable evaluations of drug effects.