Intermediate channelling

Even beyond this, it should be clear that the large clamp voltage of say 100 mV may already lead to the inactivation of larger channels, and, still worse, the excision of the cell membrane itself may inactivate channels. It is not surprising then that the current literature gives a grossly distorted view of the world of Cl -channels. It is full of large and intermediate channels, but much less data are available on small channels. This analytical problem can be overcome by other patch clamp techniques. 

Nada MA, Rhead WJ, Sprecher H, Schulz H, Roe CR (1995) Evidence for intermediate channeling in mitochondrial beta-oxidation. J Biol Chem 270 530-535... 

The second part of the reaction requires pyridoxal phosphate (Fig. 22-18). Indole formed in the first part is not released by the enzyme, but instead moves through a channel from the a-subunit active site to the jS-subunit active site, where it condenses with a Schiff base intermediate derived from serine and PLP. Intermediate channeling of this type may be a feature of the entire pathway from chorismate to tryptophan. Enzyme active sites catalyzing different steps (sometimes not sequential steps) of the pathway to tryptophan are found on single polypeptides in some species of fungi and bacte-... 

Yao, K.-W., and Schulz, H. (19%). Intermediate channeling on the trifunctional oxidation complex from pig heart mitochondria. J. Biol. Chem. 271,17816-17820. 

Calculations were done for J 0 and j = 0 In Initial and final channels. Hence Initially and finally one has 1=0 from the triangle rule. Our x hasls was restricted to j = 0 which Implies that 1=0 also In Intermediate channels. As a result ours Is an s-wave model calculation, which Is however converged In other expansions. The selection rule for this case Is... 

Steady-state kinetic analysis afforded evidence for intermediate channeling in the lumazine synthase/ riboflavin synthase complex. Briefly, the conversion of 6,7-dimethyl-8-ribityllumazine molecules that have been newly formed by the lumazine synthase module of the protein complex are more rapidly converted to riboflavin than molecules from the bulk solvent. The topological constraint by the capsid is believed to cause this phenomenon. It has been proposed that the channels along the five-fold axes could serve as port of entry and exit for substrates and products. ... 

Intermediate channeling resp. substrate channeling has been reported for heavy riboflavin synthase. At low substrate concentrations, 6,7-dimethyl-8-ribityllumazine formed in situ by the lumazine synthase capsid is more rapidly converted by the resident riboflavin synthase as compared to 6,7-dimethyl-8-ribityllumazine in the bulk solvent. Retarded evasion of the newly formed lumazine synthase product from inside the capsid has been proposed as a tentative explanation. 

In general, this type of channel conflict can undermine attempts to develop cooperative relations in the intermediated channel, possibly to the ultimate detriment of all involved parties. 

Coordination in Multi-Channel Systems With Both Manufacturer-Owned And Intermediated Channels... 

The monopolist manufacturer, which has infinite capacity and no operating costs, sets the wholesale price in the intermediated channel. Intermediaries are uniformly distributed on a unit interval, differentiated by their per-item transaction cost ki. Each intermediary determines first whether to enter. On entering, an intermediary chooses a price pi to charge and buys an amount equal to the expected demand in each search period. is the equilibrium number of intermediaries (actually an interval size) who will be in the market. 

Channeling of intermediates is seen in the phenomenon of catalytic facilitation, i.e., preferred transformation of intermediates formed by the enzyme complex, compared to that of externally added intermediates. Channeling may increase catalytic efficiency by decreased diffusion times or direct transfer of intermediates. It may also decrease the lag phase prior to steady-state production of the final product and allow a finer tuning of the overall activity by coordinate activation and inhibition. 

Where H is the charmel height (the smaller dimension in a rectangular channel), tw,av the average wall shear stress, V the kinematic viscosity, and p the density of the fluid. In internal flows, the laminar to turbulent transition in abrupt entrance rectangular ducts was found to occur at a transition Reynolds number Ret = 2200 for an aspect ratio ac = I (square ducts), to Ret = 2500 for flow between parallel planes with = 0 [4]. For intermediate channel aspect ratios, a linear interpolation is recommended. For circular tubes. Ret = 2300 is suggested. These transition Reynolds number values are obtained from experimental observations in smooth channels in macroscale applications of 3 mm or larger hydraulic diameters. Their applicability to microchannel flows is still an open question. 

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