A number of amino acids, most noticeably asparagine, were capable of inducing ornithine decarboxylase in H-35 rat hepatoma cells. The effective amino acids were all neutral and were substrates of the Na+-dependent transport systems A, ASC and N. Transport inhibitor studies indicated that there was an excellent correlation between the level of enzyme activity induced and the initial rate of asparagine transport into the cells by the A and the N systems. It is proposed that the activation of the Na+-dependent, pH-sensitive amino acid transport systems and the subsequent intracellular pH and ionic perturbation constitute part of the initiation signals for cell activation.
Amino Acids Animals