PubMed Health⌕ Search

Biomedical subjects

J S Kahn

Publications and source records attributed to J S Kahn.

At least 37 records · Page 2Linked to original sources
PubMed1982

The epsilon Subunit of the Chloroplast Coupling Factor 1 from Euglena gracilis: A Possible Role in Controlling ATPase Activity.

The coupling factor from chloroplasts (CF(1)) of Euglena gracilis Z strain is an active ATPase in situ, and its activity cannot be increased by treatment with trypsin or heating as is the case with the CF(1) from other sources. The smallest subunit of CF(1), the epsilon subunit, is supposed to be involved in controlling the ATPase activity. We have devised a simple technique for rapid and large-scale isolation of this subunit. The epsilon subunit from Euglena CF(1), although having only a limited inhibitory effect on Euglena CF(1), drastically inhibited the ATPase activity of heat-activated spinach CF(1). The inhibition of spinach CF(1) could be reversed by passage through Sephadex G-50 or by a second heat activation. An antibody to the epsilon subunit of Euglena CF(1) cross-reacted only weakly with CF(1) from spinach, Sorghum, Kalanchoë, or Anacystis nidulans, but reacted well with whole Euglena CF(1) in addition to its epsilon subunit. The antibody increased the ATPase activity of Euglena and Anacystis CF(1) and of unactivated or partially activated spinach CF(1). The results suggest that the function of the epsilon subunit in Euglena CF(1) is similar to its function in CF(1) from other sources. The data also suggest that changes induced in spinach CF(1) by activation involves modifications in subunits other than the epsilon one.

Journal Article↗
PubMed1977

Some biochemical properties of mitochondria isolated from Euglena gracilis.

Mitochondria were isolated from Euglena gracilis strain Z by pressure-breakage of the cells and sucrose-cushion centrifugation. Multiple peaks (2-4) were observed in the rate of phosphorylation with Mg-ADP-phosphate concentration curves. The phosphorylative and oxidative activities were highest with NADH as the substrate, moderate with succinate, and lowest with glutamate. Inhibition of phosphorylation with 2,4-dinitrophenol and carbonyl cyanide, m-chlorophenylhydrazone gave sigmoidal concentration curves, with the extent of inhibition by DNP depending on the substrate used. Inhibition of phosphorylation by valinomycin, atractyloside, or carboxyatractyloside was only approximately 60%. Oligomycin inhibited phosphorylation in 2 phases at low and high concentrations; it inhibited Mg-ATPase in a sigmoidal fashion. Both phosphorylation and oxidation had discontinuities in Arrhenius plots at 34 C and 18 C. The relative Mg2+-dependent nucleoside triphosphatase activity was: 1 for ATP and GTP, 0.6 for ITP, 0.15 for CTP and UTP; with Ca2+ in place pf Mg2+ this activity was 0.35. Both DNP and CCCP stimulated the Mg-ATPase 50-200%. The optimal pH for the stimulation was approximately 7 regardless of the uncoupler used, and approximately 8 without the uncouplers. The few differences observed between mitochodria from Euglena and those from other sources are probably due to the fragmentation of the reticular mitochondrial structure during isolation and not to unique characteristics of these mitochondria.

Adenosine Triphosphatases↗
PubMed1972

Light Activation of Mg-dependent Adenosine 5'-Triphosphatase in Isolated Euglena Chloroplasts.

Enhancement of Mg(2+)-dependent ATPase activity in Euglena gracilis chloroplasts by light in the presence of a sulfhydryl compound has been demonstrated. A number of uncouplers and energy transfer inhibitors were studied for their effects on the light enhancement of ATPase activity simultaneously with their effects on photophosphorylation. Results suggest that the light-enhanced ATPase activity in Euglena chloroplasts is an energy-initiated process and that the energy is supplied through electron flow upon illumination of the chloroplasts. However, by studying the difference in their response toward the various uncouplers and inhibitors, it seems that the two processes (photohydrolysis of ATP and photophosphorylation) share only the latter part of their energy-transferring pathway.

Journal Article↗
PubMed1970

Absence of a common intermediate pool among individual enzyme chains of the energy-conservation pathway in chloroplasts of Euglena gracilis.

Tri-n-butyltin chloride is a specific inhibitor that binds stoicheiometrically and irreversibly with the ATP-synthesizing sites of chloroplasts. Titration of Euglena chloroplasts with tri-n-butyltin chloride shows about six ATP-synthesizing sites per molecule of cytochrome c(552) or per 380 molecules of chlorophyll. This system was used to study the possibility of linkage between individual enzyme chains of the energy-conservation pathway or the possible existence of a common pool of an intermediate in this pathway. The inhibition of ATP synthesis by tri-n-butyltin chloride at low rates of electron transport (low light-intensities, NADP(+) or ferricyanide as electron acceptor) agrees with a kinetic model of two to four ATP-synthesizing sites per energy-conservation chain. At high rates of electron transport, however, the results occasionally agree with a model of 20 or more sites per chain. The results are interpreted as indicating the absence of a common intermediate pool, but the presence of a limited degree of linkage between individual chains. It also indicates the presence of two energy-conservation sites in these chloroplasts.

Adenosine Triphosphate↗