Biosynthesis of yeast mannan. Characterization of mannan-synthesizing enzyme systems from mutants defective in mannan structure

The yeastSaccharomyces cerevisiae X2180-1A (wild) and its mutants X2180-1A-4 (mnn 1) and X2180-1A-5 (mnn 2) defective in mannan biosynthesis were used as enzyme sources to catalyzein vitro mannosyl transfer from GDP-[¹⁴C-U]-mannose to endogenous glycoproteins as well as to exogenous, low-molecular weight acceptors. While the enzyme preparation from the wild strain exhibited all mannosyl transferase activities involved in mannan biosynthesis by catalyzing the synthesis of characteristic mannoprotein, the enzyme frommnn 1 mutant failed to catalyze the synthesis of α(1→3) mannoside linkages both with endogenous as well as with exogenous acceptors. The enzyme preparation from themnn 2 mutant catalyzed the formation of mannoprotein very similar to that obtained with the enzyme from the wild strain. The most important difference was the formation of a higher number of unsubstituted mannosyl units in the α(1→ 6) linked mannan backbone. The observed results support the hypothesis that in themnn 1 the mutation has altered the structural gene involved in biosynthesis of an α(1→3) mannosyl transferase catalyzing the addition of α(1→3) linked mannosyl units to α(1→2) linked mannotrioses in the polysaccharide side chains and in the oligosaccharides attached to serine and/or threonine in the protein part of mannan molecule. Themnn 2 mutant represents most probably a kind of regulatory mutation where the activity of an α(1→2) mannosyl transferase adding the mannosyl units directly to α(1→6) linked backbone in the outer region of polysacoharide part of yeast mannan is repressedin vivo but becomes significantin vitro.     

Effect of gibberellic Acid on crown gall tumor induction in aging primary pinto bean leaves

Gibberellic acid was tested for its effect on tumor induction by Agrobacterium tumefaciens in primary pinto bean (Phaseolus vulgaris) leaves in various stages of development. The hormone was found to promote tumor induction in partially aged leaves but did not effect tumor induction in very young leaves or in fully matured leaves. It is suggested that the natural loss of susceptibility to tumor induction in maturing pinto bean leaves is associated with a concomitant loss of endogenous gibberellins and/or a sensitivity to gibberellins.     

A comparison of the nitrogen metabolic networks of Kluyveromyces marxianus and Saccharomyces cerevisiae

In grape must, nitrogen is available as a complex mixture of various compounds (ammonium and amino acids). Wine yeasts assimilate these multiple sources in order to suitably fulfil their anabolic requirements during alcoholic fermentation. Nevertheless, the order of uptake and the intracellular fate of these sources are likely to differ between strains and species. Using a two-pronged strategy of isotopic filiation and RNA sequencing, the metabolic network of nitrogen utilization and its regulation in Kluyveromyces marxianus were described, in comparison with those of Saccharomyces cerevisiae. The data highlighted differences in the assimilation of ammonium and arginine between the two species. The data also revealed that the metabolic fate of certain nitrogen sources differed, thereby resulting in the production of various amounts of key wine aroma compounds. These observations were corroborated by the gene expression analysis.     

SMS 201-995: a very potent and selective octapeptide analogue of somatostatin with prolonged action

Stepwise modification of a conformationally stabilised analogue of the fragment of somatostatin which had been thought to be essential biologically active moiety has enabled us to synthesise the analogue H-(D) Phe-Cys-Phe-(D) Trp-Lys-Thr-Cys-Thr(ol) code-named SMS 201-995, which in vitro is three times more potent than the native hormone in inhibiting the secretion of growth hormone, which is highly resistant to degradation by pure enzymes and by tissue homogenates, which in vivo in rat and rhesus monkey is (depending on test system) at least 20 times more active than somatostatin, which is much longer acting, and which moreover in both species is much more selective in inhibiting the secretion of growth hormone than that of insulin. The compound is active by several routes of administration including the oral, is well tolerated both in laboratory animals and in man, and is currently undergoing preliminary clinical trial.     

Visual-vestibular convergence in the vestibular nuclei of the cat

Responses from neurons of the vestibular nuclei were recorded in N₂O-anaesthetized cats. Most neurons in the rostral parts of the nuclei responded to bimodal visual-vestibular stimulation, following a trapezoidal velocity profile. Both combinations of the two stimuli were tested: rotation of the animal with stationary visual field and rotation with overtaking visual field, i.e. the visual pattern running in the same direction as the turntable with twice the velocity. Some correlation of physiological data with results in corresponding psychophysical experiments were found. As a possible biological function of visual-vestibular convergence a phylogenetic solution for discrimination of body and outer world movement is discussed.