The relation of electron transport and photophosphorylation to conformational changes in chloroplasts

1. The rate of the Hill reaction and photophosphorylation, and the ratio of ATP produced to the electron flow are shown to be strongly dependent on the solute concentration of the medium.

2. A large part, but not all, of the requirement for MgCl₂ or phosphate in photophosphorylation can be replaced by SrCl₂ or other solutes.

3. In two-stage photophosphorylation, solutes are required during the light-activation stage.

4. The presence of solutes causes marked changes in the packed volume of the chloroplasts, and their light-scattering properties. These changes are essentially complete within 1 min.

5. The effectiveness of solutes in enhancing the rate of electron transport and photophosphorylation parallels their effectiveness in inducing conformational changes in chloroplasts.

6. It is suggested that the solutes act by inducing a conformational change of the chloroplast structure which is more optimal for electron transfer and coupled phosphorylation.     

A method for measuring the internal pH in illuminated chloroplasts based on the stimulation of proton uptake by amines.

A simple method for measuring the internal pH of chloroplasts during steady-state illuminations based on the stimulation of proton uptake by monofunctional amines was developed. Predictions of a mathematical derivation concerning the dependence of the stimulation on the amine concentration, the internal volume, the pK of the amine and the external pH have been verified experimentally. To circumvent uncoupling and swelling due to large internal accumulation of amines extrapolation of the stimulation to low amine concentrations was suggested and shown to lead to valid values. Alternatively, swelling could be largely reduced in a medium containing potassium aspartate and valinomycin.     

Light Modulation of Enzyme Activity in Chloroplasts: Generation of Membrane-bound Vicinal-Dithiol Groups by Photosynthetic Electron Transport

Inhibitor experiments indicate that photosynthetic electron transport is required for light activation of the pea (Pisum sativum) leaf chloroplast enzymes NADP-linked glyceraldehyde-3-phosphate dehydrogenase, NADP-linked malic dehydrogenase, ribulose-5-phosphate kinase and sedoheptulose-1,7-diphosphate phosphatase, and for inactivation of glucose-6-phosphate dehydrogenase. Modulation of the activity of the dehydrogenases and kinase apparently involves a component preceding ferredoxin in the photosynthetic electron transport chain; activation of the phosphatase involves an electron transport component at the level of ferredoxin. Modulation of enzyme activity can be obtained in a broken chloroplast system consisting of membrane fragments and stromal extract. The capacity for light regulation in this system is reduced or eliminated when the membrane fraction is exposed to arsenite in the light or to sulfite in light or dark. Light-generated vicinal-dithiols seem therefore to be involved in modulation of the activity of the enzymes included in this study.     

Adenosine triphosphate-generated transmembrane electric potential in chloroplasts

Utilizing oxonol VI as a transmembrane electric potential indicating dye, chloroplasts are shown to develop rapid transient light-induced and ATP-induced potentials. Following the large transient signal smaller steady-state potentials are maintained with either driving system. The ATP-induced potential in the dark depends upon preactivation of the light-triggered ATPase of the chloroplasts, and is inhibited by uncouplers, ionophores such as valinomycin, and energy-transfer inhibitors such as tentoxin, Dio-9 or DCCD. Nigericin increased the signal of both the light- and the ATP-induced reactions. The fact that relatively large transient membrane potentials are induced by either a dark-to-light transition or ATP in the dark provides an explanation for previously observed phenomena such as early kinetics of photophosphorylation and the ATP-induced luminescence.     

Hemodynamic physiology and thermoregulation in liposuction

Little is known about the physiology of large-volume liposuction. Patients are exposed to prolonged procedures, general anesthesia, fluid shifts, and infusion of high doses of epinephrine and lidocaine. Consequently, the authors examined the thermoregulatory and cardiovascular responses to liposuction by assessing multiple physiologic factors. The aims of their study were to serially determine hemodynamic parameters perioperatively, to quantify perioperative and postoperative plasma epinephrine levels, and to chronologically document fluctuations in core body temperature. Five female volunteers with American Society of Anesthesiologists' physical status I and II underwent moderate- to large-volume liposuction. Heart rate, blood pressure, mean pulmonary arterial pressure, cardiac index, and central venous pressure were monitored. Serum epinephrine levels and core body temperature were assessed perioperatively. The hemodynamic responses to liposuction were characterized by an increase in cardiac index (57 percent), heart rate (47 percent), and mean pulmonary arterial pressure (44 percent) (p < 0.05). Central venous pressure was not significantly altered. Maximum epinephrine levels were observed 5 to 6 hours after induction. Significant correlations between cardiac index and epinephrine concentrations were shown intraoperatively (r = 0.75). All patients developed intraoperative low body temperatures (mean 35.5 degrees C). An overall enhanced cardiac function was observed in patients subsequent to large-volume liposuction. The etiology of the altered cardiac parameters was multifactorial but may have been attributable in part to the administration of epinephrine, which counters the effects of general anesthesia and operative hypothermia. Additional explanations for raised cardiac output may be hemodilution or emergence from general anesthesia. Elevated mean pulmonary arterial pressure may be a result of subclinical fat embolism demonstrated in previous porcine studies, although fat was not observed in urine. The unchanged central venous pressure levels indicate that young healthy patients with compliant right ventricles can accommodate the fluid loads of large-volume liposuction. Overall hemodynamic parameters remained within safe limits. Within these surgical parameters, patients should be clinically screened for cardiovascular and blood pressure disorders before liposuction is undertaken, and preventative measures should be taken to limit intraoperative hypothermia.     

Electrolyte and plasma enzyme analyses during large-volume liposuction

Substantial fluid shifts occur during liposuction as wetting solution is infiltrated subcutaneously and fat is evacuated, causing potential electrolyte imbalances. In the porcine model for large-volume liposuction, plasma aspartate aminotransferase and alanine transaminase levels were elevated following liposuction. These results raised concerns for possible mechanical injury and/or lidocaine-induced hepatocellular toxicity in a clinical setting. The first objective of this human model study was to explore the effect of the liposuction procedure on electrolyte balance. The second objective was to determine whether elevated plasma aminotransferase levels were observed subsequent to large-volume liposuction. Five female volunteers underwent three-stage, ultrasound-assisted liposuction. Blood samples were collected perioperatively. Plasma levels of sodium, potassium, venous carbon dioxide, blood urea nitrogen, chloride, and creatinine were determined. Liver function analyte levels were measured, including albumin, total protein, aspartate aminotransferase, and alanine transaminase, alkaline phosphatase, gamma-glutamyl transpeptidase, and total bilirubin. To further define intracellular enzyme release, creatine kinase levels were measured. Mild hyponatremia was evident postoperatively (134 to 136 mmol/liter) in four patients. Hypokalemia was evident intraoperatively in all subjects (mean +/- SEM; 3.3 +/- 0.16 mmol/liter; range, 3.0 to 3.4 mmol/liter). Hypoalbuminemia and hypoproteinemia were observed throughout the study (baseline: 2.9 +/- 0.2 g/dl; range, 2.6 to 3.5 g/dl), decreasing to 10 to 40 percent 24 hours postoperatively (2.0 +/- 0.2 g/dl; range, 1.7 to 2.1 g/dl). Aspartate aminotransferase, alanine transaminase, and creatine kinase levels were significantly elevated after the procedure (190 +/- 47.1 U/liter, 50 +/- 7.7 U/liter, and 11,219 +/- 2556.7 U/liter, respectively) (p < 0.01). Release of antidiuretic hormone and even mildly hypotonic intravenous fluid infiltration have long been known to cause hyponatremia postoperatively. Intraoperative hypokalemia is associated with hypocarbia and respiratory alkalosis and the elevated epinephrine levels observed in the concurrent study. Factors having the greatest initial impact on diminished serum albumin and protein levels postoperatively are redistribution and hemodilution. Subsequent diminished viscosity may significantly affect postoperative hemodynamics. Elevated aspartate aminotransferase, alanine transaminase, and creatine kinase levels are associated with skeletal muscle injury, adipocyte lysis, and/or hepatic damage. Therefore, tissue injury is associated with large-volume liposuction as observed in several cellularly released enzymes. Future clinical studies are required to determine the degree of injury and specific tissues that are damaged or sensitive to mechanical trauma and/or drugs used in large-volume liposuction.