Problems of reduced heme synthesis in reticulocytes with impaired globin synthesis

Summary The mechanism by which heme synthesis is inhibited in reticulocytes with inhibited globin synthesis is not yet established. Evidence was found that the accumulated free heme does not inhibit the activity of -aminolaevulic acidsynthetase. The very early inhibition of heme synthesis may be caused by the effect of uncompleted globin chains or amino acids on the -aminolaevulic acidsynthetase or some other enzymes of the porphyrin biosynthetic chain. The accumulated free heme, the presence of which in reticulocytes with inhibited globin synthesis has been indirectly proved may reduce the iron entry to the reticulocytes which in turn can influence the synthesis of heme especially in the later periods of incubation. A feedback inhibitory effect of accumulated free heme at some critical site on the enzymes of the porphyrin biosynthetic chain cannot still be quite excluded.

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Zusammenfassung Der Mechanismus, mit dem die Häm-Synthese bei Retikulozyten mit gestörter Globulinsynthese gehemmt wird, ist noch nicht geklärt. Es wurden Anzeichen dafür gefunden, daß die akkumulierten freien Häme die Aktivität der -Aminolävulinsäuresynthetase nicht behindern. Die sehr frühe Hemmung der Häm-Synthese kann durch die Wirkung unvollständiger Globinketten oder Aminosäuren auf die -Aminolävulinsäuresynthetase oder einige andere Enzyme der biosynthetischen Porphyrinkette verursacht werden. Die akkumulierten freien Häme, deren Anwesenheit in Retikulozyten mit gehemmter Globinsynthese indirekt nachgewiesen wurde, können den Eintritt von Eisen in die Retikulozyten reduzieren, was wiederum die Synthese der Häme, besonders in den späteren Inkubationszeiten beeinflussen kann. Eine hemmende Rückkoppelungswirkung akkumulierter freier Häme an irgendeiner kritischen Stelle der Enzyme der biosynthetischen Prophyrinkette kann nicht ganz ausgeschlossen werden.

     

Cell-mediated synthesis of somatostatin

Messenger RNA from catfish pancreatic islets was translated in a wheat germ cell-free protein synthesizing system. A protein of 12,000 mol wt, preprosomatostatin, was identified by specific immunoprecipitaton with anti-catfish pancreatic somatostatin and sodium dodecyl sulfate (SDS)- polyacrylamide gel electrophoresis.     

Disorders of mineralocorticoid synthesis

Abnormalities of mineralocorticoid synthesis and/or metabolism profoundly affect the regulation of electrolyte and water balance and of blood pressure. Characteristic changes in extracellular potassium, sodium and hydrogen ion concentrations are usually diagnostic. Serious deficiency may be acquired, for example in Addison's disease, or inherited. In most of the inherited syndromes, the precise molecular changes in specific steroidogenic enzymes have been identified. Mineralocorticoid excess may be caused by aldosterone or 11-deoxycorticosterone by inadequate conversion of cortisol to cortisone by 11beta-hydroxysteroid dehydrogenase type 2 in target tissues (see Chapter 4), by glucocorticoid receptor deficiency or by constitutive activation of renal sodium channels. Changes in electrolyte balance and renin as well as the abnormal pattern of corticosteroid metabolism are usually diagnostic. Where these abnormalities are inherited (e.g. 11beta- or l7alpha-hydroxylase deficiencies, glucocorticoid remediable hyperaldosteronism (GRA), receptor defects, Liddle's syndrome), the molecular basis is again usually known and, in some cases, may provide the simplest diagnostic tests. Primary aldosteronism, although readily identifiable, presents problems of differential diagnosis, important because optimal treatment is different for each variant. Moreover, the mechanisms by which the variants develop are poorly understood. Finally, a significant proportion of patients with essential hypertension show characteristics of mild mineralocorticoid excess, for example low renin levels. Is this relevant to pathophysiology and, if so, is the effect induced via classic mechanisms of action or through newly discovered direct actions on the brain, heart and blood vessels? These questions are the subject of current research.     

Studies on memory: inhibitors of protein synthesis also inhibit catecholamine synthesis.

The rates of accumulation of newly synthesized catecholamines and endogenous catecholamine levels in mice were determined after treatment with cycloheximide, acetoxycycloheximde, puromycin, and anisomycin. The rates of accumulation were found to be decreased by all antibiotics tested, weakening the assumption that their amnestic effects are due solely to inhibition of protein synthesis.     

Mo-catalyzed asymmetric olefin metathesis in target-oriented synthesis: enantioselective synthesis of (+)-africanol

Catalytic asymmetric ring-opening metathesis (AROM) provides an efficient method for the synthesis of a variety of optically enriched small organic molecules that cannot be easily prepared by alternative methods. The development of Mo-catalyzed AROM transformations that occur in tandem with ring-closing metathesis are described. The utility of the Mo-catalyzed AROM/ring-closing metathesis is demonstrated through an enantioselective approach to the synthesis of (+)-africanol.     

Diversity-oriented synthesis of macrocyclic peptidomimetics

Structurally diverse libraries of novel small molecules represent important sources of biologically active agents. In this paper we report the development of a diversity-oriented synthesis strategy for the generation of diverse small molecules based around a common macrocyclic peptidomimetic framework, containing structural motifs present in many naturally occurring bioactive compounds. Macrocyclic peptidomimetics are largely underrepresented in current small-molecule screening collections owing primarily to synthetic intractability; thus novel molecules based around these structures represent targets of significant interest, both from a biological and a synthetic perspective. In a proof-of-concept study, the synthesis of a library of 14 such compounds was achieved. Analysis of chemical space coverage confirmed that the compound structures indeed occupy underrepresented areas of chemistry in screening collections. Crucial to the success of this approach was the development of novel methodologies for the macrocyclic ring closure of chiral α-azido acids and for the synthesis of diketopiperazines using solid-supported N methylmorpholine. Owing to their robust and flexible natures, it is envisaged that both new methodologies will prove to be valuable in a wider synthetic context.     

The essence of total synthesis

For the past century, the total synthesis of natural products has served as the flagship of chemical synthesis and the principal driving force for discovering new chemical reactivity, evaluating physical organic theories, testing the power of existing synthetic methods, and enabling biology and medicine. This perspective article seeks to examine this time-honored and highly demanding art, distilling its essence in an effort to ascertain its power and future potential.     

Enzymatic synthesis of glycosaminoglycan heparin

Heparin and its low molecular weight heparin derivatives, widely used as clinical anticoagulants, are acidic polysaccharide members of a family of biomacromolecules called glycosaminoglycans (GAGs). Heparin and the related heparan sulfate are biosynthesized in the Golgi apparatus of eukaryotic cells. Heparin is a polycomponent drug that currently is prepared for clinical use by extraction from animal tissues. A heparin pentasaccharide, fondaparinux, has also been prepared through chemical synthesis for use as a homogenous anticoagulant drug. Recent enabling technologies suggest that it may now be possible to synthesize heparin and its derivatives enzymatically. Moreover, new technologies including advances in synthetic carbohydrate synthesis, enzyme-based GAG synthesis, micro- and nano-display of GAGs, rapid on-line structural analysis, and microarray/microfluidic technologies might be applied to the enzymatic synthesis of heparins with defined structures and exhibiting selected activities. The advent of these new technologies also makes it possible to consider the construction of an artificial Golgi to increase our understanding of the cellular control of GAG biosyntheses in this organelle.     

Models of speech synthesis.

The term "speech synthesis" has been used for diverse technical approaches. In this paper, some of the approaches used to generate synthetic speech in a text-to-speech system are reviewed, and some of the basic motivations for choosing one method over another are discussed. It is important to keep in mind, however, that speech synthesis models are needed not just for speech generation but to help us understand how speech is created, or even how articulation can explain language structure. General issues such as the synthesis of different voices, accents, and multiple languages are discussed as special challenges facing the speech synthesis community.     

Photoelectrochemical synthesis of DNA microarrays

Optical addressing of semiconductor electrodes represents a powerful technology that enables the independent and parallel control of a very large number of electrical phenomena at the solid-electrolyte interface. To date, it has been used in a wide range of applications including electrophoretic manipulation, biomolecule sensing, and stimulating networks of neurons. Here, we have adapted this approach for the parallel addressing of redox reactions, and report the construction of a DNA microarray synthesis platform based on semiconductor photoelectrochemistry (PEC). An amorphous silicon photoconductor is activated by an optical projection system to create virtual electrodes capable of electrochemically generating protons; these PEC-generated protons then cleave the acid-labile dimethoxytrityl protecting groups of DNA phosphoramidite synthesis reagents with the requisite spatial selectivity to generate DNA microarrays. Furthermore, a thin-film porous glass dramatically increases the amount of DNA synthesized per chip by over an order of magnitude versus uncoated glass. This platform demonstrates that PEC can be used toward combinatorial bio-polymer and small molecule synthesis.     

Metal-induced infidelity of DNA synthesis

Summary A number of metals have been demonstrated to be mutagens in procaryotic and eucaryotic organisms as well as carcinogens in experimental animals. Epidemiologic studies have indicated that Ni, Cr, and As are involved in human carcinogenesis. We have hypothesized that the active molecular species is the cation and that metal induced mutations result from incorrect base-substitutions during DNA replication. This is supported by the observations that metal ions diminish the fidelity of DNA synthesis in vitro using a variety of DNA polymerases. There is a significant correlation between the metals that decrease fidelity and those that have been reported to be mutagenic and carcinogenic. Thus, metal carcinogens are no exception to the general postulate that carcinogens can be identified by their effects on DNA.