Browsing by Author "Devendra P. Singh"

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Ammonium Transport in Unicellular Cyanobacterium Anacystis nidulans
(1985) A.K. Kashyap; Devendra P. Singh
Anacystis nidulans IU 625, grown on nitrate, has been shown to possess two ammonium (NH+4) uptake systems; the high- (Km = 50 μM, Vmax = 2 nmol min−1 mg−1 protein) and low-affinity (Km = 357 μM, Vmax = 10 nmol min−1 mg−1 protein) systems. The two uptake systems were specific for NH+4 since methylamine competitively inhibited both the uptake systems (high-affinity K1 = 100 μM, low-affinity Ki = 833 μM). The pH profile of the uptake systems suggested that the high-affinity system was maximally operative at pH 7.4 and the low affinity system at pH 5.2. The low affinity system was suppressed in cells grown on nitrate or ammonium while the high-affinity system was not completely repressed (52 and 36 % respectively). Both the transport systems were light-dependent and sensitive to DCMU. Effect of other metabolic inhibitors (DCCD, HOQNO, NEM) revealed that energy generated as a result of ATP hydrolysis was more important for NH+4 uptake by the low-affinity system, whilst the high-affinity system was more sensitive to protonophore FCCP suggesting an involvement of proton gradient of membrane. Concentrations of MSX non-inhibitory to GS activity during the course of experimentation showed mixed type inhibition of NH+4 uptake by the high-affinity system and non-competitive inhibition of the low-affinity system. Mutant A. nidulans/Mn 10 showed only one high-affinity system (Km = 250 μM, Vmax = 10 nmol min−1 mg−1 protein) maximally operative at pH 7.4, comparable to the lowaffinity system of the wild type. It is concluded that NH+4 uptake in A. nidulans is genetically controlled. © 1985, Gustav Fischer Verlag, Stuttgart. All rights reserved.
Cu2+ transport in the unicellular cyanobacterium anacystis nidu lans
(1985) Devendra P. Singh
Cu2+ uptake by A. nidulans wild type was concentration dependent and followed Michaelis-Menten type kinetics with saturating concentration at 25 μM. A Lineweaver-Burk plot of the data revealed an apparent Kmof 16.6 μM. and a Vmaxvalue of 2.5 nmol mg-1 protein min-1. No characteristic pH profile was evident for Cu2+ uptake in a pH range of 4.0-9.0, although the highest uptake rate was at pH 4.0. Uptake was sensitive to protonophore FCCP, suggesting the involvement of a proton gradient. Uptake was uninhibited in the dark or in the presence of DCCD, indicating that energy generated through ATP hydrolysis may not be directly involved in the uptake process. Genetic control of the transport was suggested on the ground that mutants differed among themselves as well as from the wild type in terms of Kmand Vmaxvalues. © 1985, Applied Microbiology, Molecular and Cellular Biosciences Research Foundation. All rights reserved.