A system for viably maintaining a stirred suspension of multicellular spheroids during NMR spectroscopy.

We have developed a system for the perfusion of a stirred suspension of multicellular spheroids during nuclear magnetic resonance spectroscopy. Measurement of the medium temperature, pH, oxygen tension, and glucose and lactate concentrations demonstrated that the macroenvironmental conditions around the spheroids during perfusion matched those in standard spinner culture flasks. Spheroids cultured in the NMR perfusion chamber for up to 48 h were virtually identical to spheroids cultured under standard conditions in terms of volume and cell number growth, the extent of central necrosis, cellular clonogenicity, and proliferative status. To avoid problems in interpreting the NMR spectra, we have used a medium containing 10% of the normal inorganic phosphate concentration; comparative growth and NMR studies showed that this medium had no effect on the results reported. 31P NMR spectroscopic analysis demonstrated that the mean pH, nucleotide triphosphate (NTP) to inorganic phosphate (Pi) ratio, the total amount of NTP, and the total energy charge were essentially constant over 8 h of analysis. Stopping the stirring of the spheroid culture during analysis resulted in depletion of the nucleotide phosphate pool in 30 min, with an accumulation of Pi and a shift to a more acid intracellular pH. This effect could be reversed if stirring was resumed within 30 min. Stopping the perfusion while maintaining stirring resulted in a deterioration of the 31P spectra until no high energy phosphates remained at 120 min and the pH fell to approximately 6. This effect was also partially reversible after 30 min of reperfusion, with recovery to a normal 31P spectrum requiring 10 h. The combination of the spheroid model system with 31P NMR spectroscopic analysis will provide a powerful tool for investigating basic questions about the regulation of tumor cell energy metabolism and viability.

A fluorometric study of the interaction of bradykinin with lipids.

The interaction of bradykinin (BK) with lipids has been followed by steady-state fluorescence measurements. Addition of either cerebroside sulfate (CS) or phosphatidylinositol (PI), solubilized with the nonionic surfactant C12E8, to BK or its analogue [Gly6]-BK enhances the relative fluorescence intensity of peptide emission at 288 nm. Fluorometric titration of the peptide with lipid has been used to quantitate the interactions in terms of stoichiometry and equilibrium constant. Job's method of continuous variation for the BK-CS interaction gave a stoichiometry of 1:2 for the complex. The value of the equilibrium constant, K, for the interaction of either BK or [Gly6]-BK with CS is 1.5.10(4) M-1. The BK-PI interaction is weaker; K = 5.0.10(3) M-1. Although electrostatic forces no doubt play a major role in these interactions, measurements on the model peptide Gly-Phe-Gly indicate that the phenylalanine residues of BK are disposed in the hydrophobic environment provided by the lipid-C12E8 mixed micelle. 13C-NMR measurements on [99% 13C alpha-Gly6]-BK show that there is no change in its cis/trans ratio upon interaction with CS. The increase in the relative fluorescence intensity of BK accompanying its cooperative interaction with sodium dodecyl sulfate (SDS) implicates the role of hydrophobic forces in this interaction as well. These results bear on the interpretation of the changes in circular dichroism (CD) of BK caused by SDS.

Theory of counterion electrophoresis. Guidelines for determination of ligand-binding parameters.

A theory is formulated to provide guidelines for the quantitative interpretation of steady-state counterion electrophoretic patterns (T.-H. Ueng and F. Bronne, Arch. Biochem. Biophys. 197 (1979) 205) in terms of intrinsic ligand-binding constant and number of binding sites on the protein molecule. Briefly, the prescribed procedure calls for extrapolation of the steady-state binding constant to infinite dilution of protein to obtain a quantity which is the product of a readily evaluated kinetic factor and the intrinsic binding constant. On the other hand, extrapolation of the steady-state number of binding sites to infinite dilution can probably be dispensed with if determined at a reasonably low protein concentration.

Theory of electrophoresis of reacting systems as applied to the sulfhydryl oxidation of creatine kinase.

In an attempt to explain the unusual electrophoretic behavior of fish muscle creatine kinase, a phenomenological theory of transport of reacting systems has been formulated for the electrophoresis of a sulfhydryl protein undergoing oxidation in the presence of a gradient of molecular oxygen. The model assumes slow O2-oxidation of sulfhydryl groups followed by rather rapidly reversible sulfhydryl-disulfide interchange with concomitant change in the electrophoretic mobility of the protein. The computed electrophoretic patterns for this model exhibit a sharp, unimodal ascending boundary but a bimodal descending boundary in which the proportions of the two peaks are time dependent. There is a striking similarity between the theoretical patterns and their experimental counterparts (M.D. Doherty, D.A. Bergman, V.M. Re-Miller, and D.J. Winzor, 1980, Arch. Biochem. Biophys. 202, 558-564); and hence support for consideration of the electrophoresis of fish muscle creatine kinase in these terms.

Phytochemical screening of some Rocky Mountain plants.

Fifty-four species of plants from 36 genera and 21 families were collected in the mountains and high plains of northern Colorado. Extracts were tested for alkaloids, cytotoxicity, antitumor activity and IP toxicity in mice. A few were tested for insect attractant or deterrent properties. Alkaloids were found in 23 species, 15 showed cytotoxicity, and 27 exhibited IP toxicity. Four extracts showed insect deterrent properties, and three proved to attractant. None of the extracts showed useful antitumor activity. High alkaloid content and/or activity in several of the screens can be used to identify species and genera worthy of detailed phytochemical investigation.