Lipid and Temperature Dependence of Membrane-Bound ATPase Activity of Acholeplasma laidlawii

Abstract

Arrhenius plots (15–45 °C) of the ATPase activity of Acholeplasma laidlawii membranes enriched with either arachidoyl or saturated short-chain groups exhibited a pronounced discontinuity in slope around 25–30 °C, absent in oleoyl-enriched membranes. The membrane lipid fluidity was measured with a stearic acid spin label. At the growth temperature (37 °C) the membrane lipid fluidity was identical for all three kinds of enriched membranes. For membranes enriched with saturated acyl chains, a plot of the electron paramagnetic resonance anisotropy parameter 2T11vs. the reciprocal of temperature showed a biphasic profile with a discontinuity in slope around 25–30 °C. For oleoyl-group enriched membranes this plot yields only a straight line between 15 and 50 °C. Thus, lipids do play a role in the functioning of the membrane-bound ATPase. This enzyme is probably localized in the more fluid regions of the membrane.

Control of membrane lipid fluidity in Acholeplasma laidlawii

“…A typical EPR spectrum of the 5 NS spin label has been shown elsewhere [12]. A greater value of the hyperfine splitting 2 T II reflects restricted rotational motion and therefore indicates a more viscous environment around the spin probe [13].…”

The mycoplasmas.

“…According to McElhaney (174), up to about one-half of the membrane lipid in A. laidlawii may be transformed to the gel state without apparent effects on cell growth, and the existence of less than one-tenth of the membrane lipid in a fluid state is sufficient to support some cell growth and replication, albeit at greatly reduced rates. Once the lipid bilayer totally crystallizes, cells stop growing and the membrane loses its elasticity, so that the cells lyse rather than swell when placed in hypotonic solutions (336); the permeability of the cells to nonelectrolytes, such as glycerol (175), and the valinomycin-induced leakage of K+ and Rb+ (335) are reduced to zero; and the activities of some membrane-associated enzymes drop THE MYCOPLASMAS 439 sharply (69,133,263,271). If these and other harmful effects are to be avoided, a mechanism for regulating membrane fluidity becomes essential.…”

TEMPERATURE DEPENDENCE OF DELAYED LIGHT EMISSION IN THE 6 to 340 MICROSECOND RANGE AFTER A SINGLE FLASH IN CHLOROPLASTS

“…Paramagnetic spin labcls, when incorporated into biological membranes, provide information about the fluidity of their environment (Gaffney, 1974). Various spin labels have been used to detect membrane lipid phase transitions in microorganisms (Tourtellotte et ul., 1970;Sackmann et al, 1973;Hsung et al, 1974), animal cells (Lyons and Raison, 1970;Wisnieski et al, 1971;McMurchie et al, 1973;Raison and McMurchie, 1974) and plant cells (Shneyour et al, 1973;. We used 12NS to determine if the thylakoid membrane lipids in our samples undergo phase transitions that could be correlated with the delayed light emission Arrhenius plot discontinuities.…”