Statement

In October 1977, Mr O’Halloran joined my laboratory as a graduate research assistant and was responsible for setting up an experimental system for investigating the transport of amino acids in pig kidney microvillar vesicles. The results he produced showed a statistically significant effect at low concentrations of a proteinase inhibitor, phosphoramidon, on L-leucine transport. Four compounds with chelating properties, EDTA, 1 ,lO-phenanthroline, dithiothreitol and cysteine, were also shown to be strongly inhibitory and these results, too, were reproduced in several experiments. A paper based on these results, pointing out some similarities and differences between the properties of the leucine transport system and those of an endopeptidase in the same membrane, appeared in FEBS Letters [ 11. In October 1979, another graduate joined my laboratory in order to extend these findings to the transport of other amino acids in the same vesicle preparation. Differences from the published results were soon apparent and a reinvestigation of the experiments on leucine transport was undertaken. Except for some positive results showing inhibition by 1 ,I O-phenanthroline (which also inhibited the transport of L-proline, L-alanine and D-glucose), the other compounds did not inhibit at the published concentrations (I. S. F&her and A. J. Kenny, unpublished observations). Mr O’Halloran also performed four experiments in which the reagents were coded. In one, o-phenanthroline and dithiothreitol inhibited at 100 PM and phosphoramidon at 1 mM. The other three experiments were negative. From the evidence now available, I no longer believe that the results published in [l] can be confidently attributed to the effecters studied (with the exception of 1 ,lO-phenanthroline) but were instead derived from extraneous factors in the experiments, such that apparently significant data were produced. Attempts to identify the nature of these factors have failed. Phosphoramidon, EDTA, dithiothreitol and cysteine do not cause significant and reproducible inhibition of L-leucine transport, except at concentrations too high to be regarded as site-specific. Nor, too, has any effect of other chelating agents, e.g. 8-hydroxyquinoline and a,cu’-bipyridyl, been demonstrated. There is therefore no evidence to suggest that the leucine transport system is dependent on a metalloprotein, nor that it is similar in any way to the microvillar membrane endopeptidase. I profoundly regret any confusion that the publication [l] may have caused.