EVIDENCE FOR AN AMINO ACID TRANSPORT SYSTEM IN NUCLEI ISOLATED FROM EMBRYONIC HEART

Nuclei isolated from embryonic myocardium of the chick possess an ATP phosphohydrolase and are capable of accumulating amino acid in a diffusible form in large excess of environmental levels. The enzyme is of relatively high specific activity and shows preference for ATP compared to other possible substrates. Properties common to both the enzyme and to net amino acid uptake are requirements for ATP, Mg++, Na+ or K+ and a critical level of Ca++. In the presence of Na+ or K+, both l‐ and d‐forms of several amino acids will further stimulate ATP hydrolysis. The latter stimulation by α‐alanine and the net uptake of this amino acid can both be completely inhibited by similar concentrations of ouabain, EGTA and excess Ca++. Ouabain has no effect on basic Mg++‐activated ATP hydrolysis or that stimulated by the addition of Na+ or K+. It is concluded that these nuclei possess an ATP phosphohydrolase‐linked transport system for α‐alanine and probably for other amino acids. Implications of this transport system are discussed relative to the ultrastructure and compartmentalization of the cardiac cell. Copyright © 1968, Wiley Blackwell. All rights reserved