Hormonal regulation of the alpha-ketoglutarate dehydrogenase complex in the isolated perfused rat liver

The metabolic flux through the alpha-ketoglutarate dehydrogenase reaction in perfused livers was monitored by measuring the rate of 14CO2 production from [1-14C]alpha-ketoglutarate. The rates of 14CO2 production and glucose production from [1-14C]alpha-ketoglutarate were increased with increasing perfusate alpha-ketoglutarate concentrations. Vasopressin, angiotensin II, and the alpha 1-adrenergic agonist phenylephrine stimulated transiently by 2.5-fold the metabolic flux through the alpha-ketoglutarate dehydrogenase reaction in the presence and absence of Ca2+ in the perfusion medium. High concentrations of glucagon (1 x 10(-8) M) and 8-p-chlorophenylthio-cAMP (100 microM) (data not shown) also stimulated transiently the metabolic flux through the alpha-ketoglutarate dehydrogenase reaction. However, lower glucagon concentrations (1 x 10(-9) M) stimulated the rate of 14CO2 production from [1-14C]alpha-ketoglutarate only under conditions optimized to fix the cellular oxidation-reduction state at an intermediate level, when glucagon (1 x 10(-9) M)-mediated elevation of cAMP content was greater than that observed under highly oxidizing and reducing conditions. These data indicate that agonists which increase cytosolic free Ca2+ levels stimulate the metabolic flux through the alpha-ketoglutarate dehydrogenase complex. Furthermore, the data presented here demonstrate for the first time that physiological glucagon concentrations stimulate the metabolic flux through the alpha-ketoglutarate dehydrogenase reaction only under conditions known to be optimal for glucagon-mediated Ca2+ mobilization in the isolated perfused rat liver.     

Purification and specificity of prolyl dipeptidase from bovine kidney.

Prolyl dipeptidase (iminodipeptidase, L-prolyl-amino acid hydrolase, EC 3.4.13.8) was purified 180-fold from bovine kidney. The enzyme which was obtained in a 10% yield was completely separated from a number of known kidney peptidases including an enzyme of very similar substrate specificity, proline aminopeptidase (L-prolyl-peptide hydrolase, EC 3.4.11.5). The specific activity of the enzyme with L-prolylglycine as substrate is 1600 units of activity per mg protein. Optimum activity of the enzyme is at pH 8.75 and the molecular weight on gel filtration was estimated to be 100 000. The isoelectric point of the enzyme is pH 4.25. Studies of substrate specificity showed that the enzyme preferentially hydrolyzes dipeptides and dipeptidyl amides with L-proline or hydroxy-L-proline at the N-terminus. Longer chain substrates with N-terminal proline were not hydrolyzed.     

Synthesis and activity against HBV of novel Tetra-seconucleoside analogues of dyphlline having the acyclic chains of ACV and HBG

Selective alkylation of dyphylline (1) with (2-acetoxyethoxy)methyl bromide (2a) or 4-acetoxybutyl bromide (2b) afforded 3'-O-[(acetoxyethoxy)methyl]dyphylline (3a) and 3'-O-(4-acetoxybutyl)-dyphylline (3b), respectively. A trans esterification process rather than alkylation of the dihydroxy-propyl side chain in 1 had taken place during the reaction with 2-p-toluoyloxy)ethyl chloride (5) to afford the respective 3'-toluoyloxy derivative 7 and not the anticipated 3'-O-[(p-toluoyloxy)ethyl]-dyphylline (6). Deacylation of 3a,b and 7 afforded 4a,b and 1, respectively. Viral screening of selected compounds against HBV has been investigated.     

Viral Membrane Protein Topology Is Dictated by Multiple Determinants in Its Sequence

The targeting, insertion, and topology of membrane proteins have been extensively studied in both prokaryotes and eukaryotes. However, the mechanisms used by viral membrane proteins to generate the correct topology within cellular membranes are less well understood. Here, the effect of flanking charges and the hydrophobicity of the N-terminal hydrophobic segment on viral membrane protein topogenesis are examined systematically. Experimental data reveal that the classical topological determinants have only a minor effect on the overall topology of p9, a plant viral movement protein. Since only a few individual sequence alterations cause an inversion of p9 topology, its topological stability is robust. This result further indicates that the protein has multiple, and perhaps redundant, structural features that ensure that it always adopts the same topology. These critical topogenic sequences appear to be recognized and acted upon from the initial stages of protein biosynthesis, even before the ribosome ends protein translation.     

Acute responses of muscle oxygen saturation during different cluster training configurations in resistance-trained individuals

This study compared the perceptual responses, physiological indicators and technical parameters between different training protocols focused on upper body exercises. A randomized crossover design was performed, and 12 trained individuals (age: 27.1 ± 5.7 years; height: 173.7 ± 10.7 cm; BMI: 23.9 ± 2.3) completed three resistance training sessions under different protocols separated by at least 72 h: traditional training (TT) (4 x 6 repetitions at 85% of 1RM with 120 s of rest between sets), cluster 1 (CL1) (4 x 2+2+2 repetitions at 85% of 1RM with 15 s of intra-rep rest and 80 s between sets), and cluster 2 (CL2) (24 repetitions at 85% of 1RM with 15 s of inter-set recovery). Before training, arterial blood pressure (BP) and repetitions to failure of pull-up and push-up (FT) were collected. Muscle oxygen saturation (SmO₂) in the chest and movement velocity were evaluated in barbell bench press during the training session. After finishing, lactate, BP, rate of perceived exertion and FT were assessed. The percentage of velocity loss (TT: 19.24%; CL1: 5.02% and CL2: 7.30%) in the bench press and lactate concentration (TT: 8.90 mmol·l^-1; CL1: 6.13 mmol·l^-1 and CL2: 5.48 mmol·l^-1) were significantly higher (p < 0.05) for TT compared to both CLs. RPE values were higher (p < 0.05) in TT compared to CL1 (7.95 a.u. vs. 6.91 a.u., respectively). No differences (p > 0.05) were found between protocols for SmO₂, BP, FT, pain or heart rate between set configurations. Cluster configurations allow one to maintain higher movement velocity and lower lactate and RPE values compared to a traditional configuration, but with similar concentrations of SmO₂.     

In vitro organogenesis from root culture segments of Bixa orellana L. (Bixaceae)

The organogenic potential of root explants derived from cultured seedlings of Bixa orellana L. (annatto) was investigated in response to different incubation conditions and either 4.44 μM 6-benzyladenine, 4.54 μM Thidiazuron, or 4.56 μM Zeatin. Explants cultured in liquid media with agitation generally showed better development of adventitious buds versus explants cultured on semi-solid media. The most adventitious buds developed from explants cultured in liquid media under a 16-h photoperiod. Use of Zeatin and Thidiazuron promoted the development of more adventitious buds than 6-benzyladenine but morphological abnormalities among regenerating shoots and plants were observed. Fewer adventitious buds developed from explants cultured in liquid media supplemented with 6-benzyladenine, but the buds gave rise to the highest percentage of morphologically normal regenerated plants. Histological analyses showed that adventitious buds originated from cell proliferation within the pericycle, opposite the protoxylem poles of the explant. Seedling root tissue is useful for in vitro propagation of B. orellana.