Potency of L-364,718 as an antagonist of the behavioral effects of peripherally administered cholecystokinin

A new antagonist of the peripheral cholecystokinin receptor, L-364,718, was found to block the reductions in food intake and exploratory activity induced by intraperitoneal administration of cholecystokinin octapeptide sulfate. L-364,718 significantly reversed the cholecystokinin-induced reduction in feeding at doses of 10 micrograms/kg - 10 mg/kg i.p. L-364,718 significantly reversed the cholecystokinin-induced reduction in exploratory activity at doses of 500 ng/kg - 10 mg/kg i.p. The time course of antagonist activity of L-364,718 was immediate to 90 minutes after intraperitoneal administration. L-364,718 had no significant effect on food intake or exploratory activity when administered alone, over the dose range of 100 ng/kg-10 mg/kg i.p. This compound appears to be at least one hundred times more potent than proglumide or benzotript as an antagonist of the behavioral effects of peripherally administered cholecystokinin.     

The key role of residue 5 in angiotensin II

The conformation–biological activity relationships in a series of angiotensin II analogs substituted in position 5 were studied. Results indicated that only analogs with β-branched residue in position 5 possess spectral and biological properties identical to that of parent angiotensin II.     

Evolutionally guided enzyme design

A combination of "rational" and "irrational" strategies for the creation of enzymes with novel properties is proving to be a powerful concept in the field of enzyme engineering. Guided by principles of physical organic chemistry, rational design strategies are used to identify suitable target enzymes and to choose appropriate molecular biological methods for engineering purposes. In contrast, irrational (or random) strategies are centered around the biological paradigm of stochastic molecular evolution. As illustrated in this review, such a hybrid approach is particularly useful for the design of new modular enzymes. (c) 1996 John Wiley & Sons, Inc.     

RasG protein accumulation occurs just prior to amoebae emergence during spore germination in Dictyostelium discoideum

Abstract RasG protein levels in dormant and germinating spores of Dictyostelium discoideum strains JC1 and SG1 were estimated by Western blotting. Ras Glevels were very low in dormant spores and remained low during the lag period, regardless of whether spores were heat activated or treated with autoactivator during the early stages of spore germination. RasG levels increased late during spore swelling just prior to the emergence stage of germination. These data are consistent with a requirement for RasG during vegetative growth.     

Genetic construction and functional analysis of hybrid polyketide synthases containing heterologous acyl carrier proteins.

The gene that encodes the acyl carrier protein (ACP) of the actinorhodin polyketide synthase (PKS) of Streptomyces coelicolor A3(2) was replaced with homologs from the granaticin, oxytetracycline, tetracenomycin, and putative frenolicin polyketide synthase gene clusters. All of the replacements led to expression of functional synthases, and the recombinants synthesized aromatic polyketides similar in chromatographic properties to actinorhodin or to shunt products produced by mutants defective in the actinorhodin pathway. Some regions within the ACP were also shown to be interchangeable and allow production of a functional hybrid ACP. Structural analysis of the most abundant polyketide product of one of the recombinants by electrospray mass spectrometry suggested that it is identical to mutactin, a previously characterized shunt product of an actVII mutant (deficient in cyclase and dehydrase activities). Quantitative differences in the product profiles of strains that express the various hybrid synthases were observed. These can be explained, at least in part, by differences in ribosome-binding sites upstream of each ACP gene, implying either that the ACP concentration in some strains is rate limiting to overall PKS activity or that the level of ACP expression also influences the expression of another enzyme(s) encoded by a downstream gene(s) in the same operon as the actinorhodin ACP gene. These results reaffirm the idea that construction of hybrid polyketide synthases will be a useful approach for dissecting the molecular basis of the specificity of PKS-catalyzed reactions. However, they also point to the need for reducing the chemical complexity of the approach by minimizing the diversity of polyketide products synthesized in strains that produce recombinant polyketide synthases.     

Growth patterns of early versus late successional multipurpose trees of the western Himalaya

In the mid-western Himalaya (altitude 1350 m, rainfall 1100 mm), multipurpose trees found as escapees in agricultural fields or naturally growing in the forests, play an important role in providing fuel, fooder and small timber to the farmers. Shoot elogation, and tree architecture of 4 year old trees of Grewia optiva, Robinia pseudoacacia and Celtis australis (early successionals), and Quercus leucotrichophora, Q. glauca and Ilex odorata (late successionals), were analyzed. All the late successional species showed a proleptic type of bud and branch production, while the early successional trees made growth through syllepsis. The shoot elongation differed significantly (P <0.05) with the crown position, and ranged from 11 to 30 cm in different species. Early successional species tended to maintain a comparatively narrow crown and showed a significantly (P <0.05) higher ramification ratio, and multilayered canopy. The late successionals, in contrast, showed a wide crown with monolayered canopy, adapted to the weak light intensity. There was only one flush of leaves in Q. leucotrichophora and Q. glauca while in the rest of the species there were two distinct flush periods. The results are important for the management of agroforestry trees.     

Effects of angiotensin II and its selective antagonists on inferior olivary neurones.

On the basis of biochemical and autoradiographic studies it has been shown that the inferior olivary nucleus (ION) contains predominantly angiotensin II (Ang II) receptors of the subtype 2 (AT2). In the present investigation we used microiontophoretic techniques to test the effect of Ang II on the spontaneous firing rate of rat neurones in the ION in vivo. Ang II excited the majority of histologically identified ION neurones. Furthermore, the antagonism of this angiotensin-induced excitation by selective angiotensin receptor blockers of subtype 1 and 2 (AT1 and AT2) was examined. The excitation could be blocked by low doses of the AT2-antagonists PD 123177 and CGP 42112A, whereas the AT1-antagonist DuP 753 was ineffective even at high doses. On a few occasions, however, ejection of the AT1-antagonist resulted in a potentiation of angiotensin-induced excitation. The results suggest that Ang II has an excitatory effect on a considerable number of ION neurones and that this effect is mediated by AT2-receptors.     

Beta-lactamase inactivation by mechanism-based reagents

The mechanistic pathway followed by the E. coli RTEM beta-lactamase has been studied with a view to clarifying the mode of action of a number of recently discovered inactivators of the enzyme. There is clear evidence that the beta-lactamase-catalysed hydrolysis of the 7-alpha-methoxycephem, cefoxitin, proceeds via an acyl-enzyme intermediate. An analysis of the inactivation reactions of all the known beta-lactam derivatives that result in irreversible loss of enzyme activity permits the identification of three structural features required for a beta-lactamase inactivator. The application of these principles suggests a new group of mechanism-based inactivators of the enzyme: the sulphones of N-acyl derivatives of 6-beta-aminopenicillanic acid that are themselves poor substrates for the enzyme. These sulphones are powerful inactivators of the beta-lactamase.