Precursor conversion

The proposed pathway for the biosynthesis of the avermectins (Fig. 3) has been described in a review (23). Some of the details are yet to be elucidated, although the steps, in general, are based on firm evidence from four types of studies incorporation of labeled precursors, conversion of putative intermediates by producing strains and blocked mutants, in vitro measurement of biosynthetic enzymes, and studies with enzyme inhibitors. The biosynthesis of the oleandrose units was elucidated from studies using and labeled glucose, which indicated a direct conversion of glucose to... 

Molybdopterin synthase is a 27 kDa protein (in its inactive resting state) that is comprised of 16 and 10 kDa subunits [67], The protein has a tendency to dissociate and the exact stoichiometry of the active synthase remains uncertain. Activation of the protein requires that the smaller subunit undergo a single sulfur-for-oxygen exchange, a finding that has been confirmed by mass spectral analysis of both active and inactive 10 kDa subunits. Since conversion of the precursor to MPT requires two sulfur atoms, it has been postulated that the active form of the synthase contains two 10 kDa subunits [67], The synthase not only provides sulfur atoms for MPT precursor conversion but also transports MPT to the apo-molybdenum (or presumably apotungsten) enzyme. 

Since the previous protocol led to low precursor conversions, we turned our attention to the second system, starting from precursor M and excess L H (Scheme 4). To confirm the validity of working off stoichiometry, we plotted in Fig. 9 the evolution of the molar mass and polymer content of an hybrid silicone prepared from precursor M and by fractionated addition of L H. The molar masses increase smoothly up to the end of the L H addition. In parallel, the polymer content grows more quickly up to a constant level. 

Investigations reveal that the precursor conversion efficiency is dependent not only on the nature of the precursor but also on the processing conditions such as... 

This TG-CVI technique allows significantly higher deposition temperatures, around 200°C higher than that of I-CVI techniques. The infiltration process is normally monitored and controlled in real time. The precursor conversion... 

Several specific enzyme activities associated with precursor conversions in the aflatoxin pathway " " have been partially purified (Fig.l 1.1) whereas others such as methyltransferases " have been purified to homogeneity. Several other enzymes involved in aflatoxin biosynthesis, such as a reductase and a cyclase, " have also been purified from A. parasiticus. A desaturase that converts VERA to VERB has been found in cell-free fungal extracts. Matsushima et al. have purified and characterized two versiconal hemiacetal acetate reductases involved in toxin synthesis, whereas Kusumoto and Hsieh purified to homogeneity an esterase that converts VHA to versiconal. ... 

Fyhr C, Garland M (1993) Phenomenological aspects of homogeneous catalysis. The case of equilibrium-controlled precursor conversion. Organometallics 12(5) 1753-1764... 

Catalyst Ru content wt.% Precursor Conversion % Product distribution C1-C5 i-C6 Bz ... 

Catalyst precursor Conversion after 15 h of reaction (%) Molar ratio H2/CO Average Ni particle size (nm) Carbon deposition (weight %)... 

Neutronic characteristics of MSRs have been explored in the literature. Flow effects were considered when calculating the effective multiplication factor and fast neutron, thermal neutron, and delayed neutron precursor distribution of the liquid-fuel MSR based on the multigroup neutron diffusion equation and delayed neutron precursor conversation equation (Zhang et ah, 2009b Cheng and Dai, 2014 Zhou et ah, 2014). Spatial kinetic models were developed for better neutronic analysis of the MSRs (Zhang et ah, 2015 Zhuang et ah, 2014). 

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