Unrestrained production of proopiomelanocortin (POMC) and its peptide fragments by pituitary corticotroph adenomas in Cushing's disease.

The hallmark of ACTH oversecretion in Cushing's disease is its partial resistance to the normal suppressive effect of glucocorticoids. Because ACTH secretion by the pituitary tumor is not normally restrained ACTH is overproduced with subsequent chronic hypercortisolism. Since peripheral tissues have retained their normal sensitivity to the action of cortisol they appropriately develop the features of Cushing's disease. The question of whether a collection of corticotroph cells, eventually arranged in an adenomatous-like fashion, is a primary pituitary event or is corticotropin-releasing factor driven has had no response so far. Clonal composition of such lesions has been determined by X chromosome inactivation using DNA probes which detect multiallelic polymorphism in females. A monoclonal pattern is found in all macroadenomas. ACTH is co-secreted with other peptide fragments derived from their common polypeptide precursor, proopiomelanocortin (POMC). As a rule POMC processing in pituitary tumors is qualitatively unaltered: plasma values of the N-terminal fragment, the joining peptide, the beta- and gamma-lipotropins, and beta-endorphin all are valid alternate markers of the tumor activity. Tumor POMC peptides including ACTH and its phosphorylated form usually show no peculiar or unexpected molecular forms in contrast with what is often found when POMC expression occurs in a non-pituitary tumor.     

The ω-endotoxin protein family displays a hydrophobic motif that might be implicated in toxicity

A computer-based analysis of hydropathy and surface probability of representative members of each class of the Cry family of proteins was performed. A highly conserved hydrophobic motif within the previously described block, D2, is present not only in lepidopteran toxin genes but also in toxins active against diptera and coleoptera. An interesting feature of this hydrophobic motif is the presence of an aspartic residue (highly hydrophilic) in its middle part. Comparison with the amino acid sequence from diphtheria toxin showed that it also contains a hydrophobic motif similar to the one present in the Bacillus thuringiensis toxins. It also contains an aspartic residue in the middle part and some speculations are presented on the function of this specific region with regard to the toxic mechanism of action.     

Expression patterns and association analysis of the porcine DHX58 gene

RIG-1 signalling is responsible for the detection of cytoplasmic viral RNA molecules. DEXH (Asp-Glu-X-His) box polypeptide 58 (encoded by DHX58) is a negative regulator of the RIG-1 signalling pathway. In human, the DHX58 gene can be upregulated and can inhibit the RIG-1 signalling pathway during viral infection. In this study, porcine DHX58 gene expression patterns were studied. According to our results, the porcine DHX58 gene was upregulated not only by the stimulation of Poly I:C but also by the stimulation of 1ipopolysaccharides (LPS). One polymorphism (g.4919G>C), detected in the ninth intron, was significantly associated with some blood parameters including the red cell distribution width of 1-day-old pigs and white blood cell counts, lymphocyte absolute counts, and platelet distribution width of 17-day-old pigs (P < 0.05). Moreover, the individuals with the genotype GG have a significantly higher mean white blood cell count than individuals with genotype CC or GC (P < 0.05). Our study indicates that DHX58 is an important gene that is associated with the immune response in swine.     

Effect of propionate and pyruvate on citrulline synthesis and ATP content in rat liver mitochondria.

Propionate inhibits citrullinogenesis when succinate (plus rotenone) or glutamate are the oxidizable substrates used. Propionate decreases the intramitochondrial concentration of carbamylphosphate by decreasing the ATP content. When the energy supply for citrullinogenesis is provided by an influx of exogenous ATP, propionate is no longer an inhibitor. Pyruvate inhibits citrullinogenesis with glutamate but not with succinate (plus rotenone) as oxidizable substrates. Propionate and pyruvate deplete mitochondrial ATP but probably by different mechanisms.     

Genome-wide analysis of N1-methyl-adenosine modification in human tRNAs

The N¹-methyl-Adenosine (m¹A58) modification at the conserved nucleotide 58 in the TΨC loop is present in most eukaryotic tRNAs. In yeast, m¹A58 modification is essential for viability because it is required for the stability of the initiator-tRNA^Met. However, m¹A58 modification is not required for the stability of several other tRNAs in yeast. This differential m¹A58 response for different tRNA species raises the question of whether some tRNAs are hypomodified at A58 in normal cells, and how hypomodification at A58 may affect the stability and function of tRNA. Here, we apply a genomic approach to determine the presence of m¹A58 hypomodified tRNAs in human cell lines and show how A58 hypomodification affects stability and involvement of tRNAs in translation. Our microarray-based method detects the presence of m¹A58 hypomodified tRNA species on the basis of their permissiveness in primer extension. Among five human cell lines examined, approximately one-quarter of all tRNA species are hypomodified in varying amounts, and the pattern of the hypomodified tRNAs is quite similar. In all cases, no hypomodified initiator-tRNA^Met is detected, consistent with the requirement of this modification in stabilizing this tRNA in human cells. siRNA knockdown of either subunit of the m¹A58-methyltransferase results in a slow-growth phenotype, and a marked increase in the amount of m¹A58 hypomodified tRNAs. Most m¹A58 hypomodified tRNAs can associate with polysomes in varying extents. Our results show a distinct pattern for m¹A58 hypomodification in human tRNAs, and are consistent with the notion that this modification fine tunes tRNA functions in different contexts.     

A molecular dynamics study of a model built Pro-36-Gly mutant derived from the potato carboxypeptidase A inhibitor protein

A 120ps molecular dynamics (MD) trajectory was calculated and analyzed for a putative Pro-36-Gly mutant of the potato carboxypeptidase A (CPA) protein inhibitor (PCIm). The mutant protein's fold shows a large degree of stability, judged from its low alpha-carbon r.m.s. deviation from the X-ray structure of the wild type PCI (PCIw). The N-terminal tail of PCIm differs slightly less from the X-ray structure than it does in PCIw, while the mutant's C-terminal tail (the primary contact site with CPA) and residues 13-17 present deviations as they approach each other. Differences in fluctuation pattern exist between PCIm and PCIw in residues 2-4 (the N-terminal tail), 13-17, 22-23, 28-31 (the secondary contact site with CPA) and 37-38 (the C-terminal tail); the latter region is rigidified in PCIm. Results show that the MD method is able to sense local perturbative effects produced by amino acid substitutions in flexible regions of protein molecules. The simulation suggests that the conformation of the C-terminal tail is less favorable for interaction with the target protein in the mutant than it is in the wild type protein. The Pro-36-Gly mutant is predicted to be a less potent inhibitor.     

Physical and enzymatic properties of a class III isozyme of human liver alcohol dehydrogenase: chi-ADH

chi-Alcohol dehydrogenase (chi-ADH), a class III isozyme characterized by its anodic electrophoretic mobility and lack of inhibition by 4-methylpyrazole, has been isolated from human liver and purified to homogeneity in a reducing medium. chi-ADH resembles other human liver ADH isozymes of classes I and II with respect to its molecular weight, dimeric structure, stoichiometry of zinc and NADH binding, and pH optima for the oxidation of alcohols. This homodimer exhibits subtle differences in its absorption spectrum and amino acid composition relative to those of other human isozymes but differs markedly from their specificity toward alcohols and aldehydes. chi-ADH oxidizes ethanol very poorly. The reaction is bimolecular, and an apparent Km cannot be discerned up to 2.3 M ethanol. The enzyme is inactive toward methanol, ethylene glycol, digitoxigenin, digoxigenin, and gitoxigenin , but alcohols with carbon chain lengths greater than four are oxidized rapidly with Km values decreasing with increasing carbon chain length. Taken jointly, the composition, structure, and enzymatic properties of the ADH isozymes purified and studied so far strongly imply that their metabolic roles, yet to be discovered, will give a new perspective to ethanol metabolism and pathology.