(~) 1989 Kluwer Academic Publishers. Printed in the Netherlands. Secondary transport of amino acids by membrane vesicles

force, solute transport Abstract. Lactococci are fastidious bacteria which require an xte nal source of amino acids and many other nutrients. These compounds have to pass the membrane. However, detailed analysis of transport processes in membrane v sicles has been hampered by the lack of a suitable proton-motive force (pmf)-generating system in th se model systems. A membrane-fusion procedure has been developed by which pmf-generating systems can be functionally incorporated into the bacterial membrane. This improved model system has been used to analyze the properties of amino acid transport systems in lactococci. Detailed studies have been made of the specificity and kinetics of amino acid transport and also of the interaction f the transport systems with their lipid environment. The properties of a pmf-independent, arginine-catabolism specific transport system in lactococci will be discussed. Abbreviations: pmf- protonmotive force, AW- transmembrane electrical potential, ApH-transmembrane pH gradient, PE- phosphatidylethanolamine, PC- phosphatidylcholine I n t roduct ion Lactic acid bacteria are of major importance to the dairy industry. Funda-mental and applied research efforts have substantial ly been expanded in recent years. This provided a considerable information about the physiology, biochemistry and genetics of these bacteria. Lactococci (previously named Streptococci) are strictly fermentat ive and derive their metabol ic energy from substrate level phosporylat ion and chemiosmotic energy-generat ing processes (Konings et al. 1988). These bacteria, with their relatively simple metabol ism make high demands on the composit ion of the growth media which has t