Oxygen consumption in Plasmodium berghei-infected murine red cells: a direct spectrophotometric assay in intact erythrocytes.

A spectrophotometric assay has been devised to measure oxygen consumption non-invasively in intact murine red cells parasitized by Plasmodium berghei. The method uses oxyhemoglobin in the erythrocytes both as a source of oxygen and as an indicator of oxygen consumption. Spectra of intact cells show broad peaks and sloping baselines due to light-scattering. In order to ascertain the number of varying components in the 370-450 nm range, the resolution of the spectra was enhanced using Fourier transforms of the frequency domain spectra. Calculation of oxygen consumption was carried out for two-component systems (oxyhemoglobin, deoxyhemoglobin) using absorbances at 415 and 431 nm. Samples prepared from highly parasitized mice (greater than 80% parasitemia, 5% hematocrit) showed oxygen consumption rates of (4-8) X 10(-8) microliter/cell per h. This rate was not attributable to the presence of white cells or reticulocytes. The rate of oxygen consumption in the erythrocytes is shown to be modulated by various agents: the respiratory inhibitors NaN3 and KCN (1 mM) reduced oxygen consumption 2-3-fold; salicylhydroxamic acid (2.5 mM) caused a 20% reduction in rate and 10 mM NaN3, completely blocked deoxygenation. Antimalarial drugs and metal-chelating agents were also tested. Chloroquine, EDTA and desferal (desferoxamine mesylate) did not decrease the deoxygenation rate of hemoglobin in parasitized cells. Quinacrine, quinine and primaquine reduced the rate of formation of deoxyhemoglobin but also produced substantial quantities of methemoglobin. The lipophilic chelator, 5-hydroxyquinoline, decreased the rate of deoxygenation one-third. The spectrophotometric assay provides a convenient means to monitor oxygen consumption in parasitized red cells, to test the effects of various agents thereon, and potentially to explore possible mechanisms for oxygen utilization.

Infrared spectroscopic study of the gel to liquid-crystal phase transition in live Acholeplasma laidlawii cells.

The temperature dependences of the infrared spectra of deuterium-labeled plasma membranes of live Acholeplasma laidlawii B cells and of the isolated plasma membranes demonstrate that the profiles of the gel to liquid-crystal phase transitions are very different. At temperatures within the range of the phase transition, the live mycoplasma is able to keep the "fluidity" of its plasma membrane at a much higher value than that of the isolated plasma membrane at the same temperature. The difference is particularly pronounced at and around the temperature of growth. Live Acholeplasma laidlawii, grown at 37 degrees C on a fatty acid depleted medium supplemented with myristic acid (C14:0), pentadecanoic acid (C15:0), or palmitic acid (C16:0), are highly "fluid"; i.e., at the temperature of growth, the fractional population of the liquid-crystalline phase is 95-100% at 37 degrees C, whereas in the case of the isolated plasma membranes the fractional population of the liquid-crystalline phase at 37 degrees C is only 58% (C14:0), 36% (C15:0), or 38% (C16:0).

Smoothing of spectral data in the Fourier domain.

Smoothing of spectral data using Fourier transforms is described and demonstrated with Lorentzian, sinc(2), and sine smoothing functions. Four parameters are defined and used to study the smoothing operation. It is also concluded that the best smoothing function is a sinc function if we require that the distortions due to the smoothing operation are smaller than the residual noise. Sine smoothing using Fourier transforms is also compared to least square smoothing in the frequency domain, and the advantages of sine smoothing are illustrated.

Noise in Fourier self-deconvolution.

A general formula for computing changes in the signal-to-noise ratio of a spectrum resulting from the Fourier self-deconvolution procedure is derived. Self-deconvolution reduces the intrinsic halfwidths of lines by a factor K, which is in practice limited by the noise in the spectrum. With the help of the derived formula, the rate of decrease in the SNR as a function of K for eight different smoothing (apodization) functions is studied. With high K values there are significant differences in the SNR as a result of the use of different smoothing functions. With K = 4 a difference of more than 1 order of magnitude between two extreme cases is demonstrated, and with K = 5 a difference of almost 2 orders of magnitude in the SNR is predicted.