Rate-determining processes in the transport of Pr3+ ions by the ionophore A23187 across phospholipid vesicular membranes. A 1H-MR and theoretical study.

Rate constants and activation parameters have been determined for the transport of Pr3+ ions by the ionophore A23187 across dipalmitoyl phosphatidylcholine vesicular membranes. The novel method described depends on the measurement of changes in chemical shift of the 1H-NMR choline head-group signals as Pr3+ is transported from outside to inside the vesicles. The determined rates are directly proportional to A23187 concentration, suggesting that the rate-determining step involves the species [Pr(A23187)](2+). A theoretical analysis of the initial stages of Pr3+ transport leads to the conclusion that diffusion over the image potential barrier is the rate-determing step. Calculation of the form and height of this barrier for the non-equilibrium state gives results which agree well with the experimental activation energy and also correctly predict a two-fold reduction in rate of transport when 7 mol % decane is present in the bilayer.

The analysis of protein in fresh meats using pulsed NMR.

The protein content of fresh meats was estimated using a pulsed nuclear magnetic resonance (NMR) spectrometer in conjunction with an alkali copper relaxation reagent. The standard deviations on all meat samples, which differed widely in fat content, were less than 0·5% in protein. A single calibration line, with a correlation coefficient of 0·999, was obtained using three lean meats. This calibration sufficed to determine the protein content of three meats with a high fat content, the results of which were in close agreement with the corresponding Kjeldahl values.