Inhibition by insulin of cardiac cathepsin D activity

IN previous studies of foetal mouse hearts in organ culture, I have demonstrated that insulin improves net protein and amino acid balance ¹ and prolongs the duration of survival and beating in vitro ². The hormone exerts its action on amino acids such as phenylalanine whose metabolic pathways in the heart are confined almost exclusively to protein synthesis and degradation, as well as on those such as valine and alanine that may enter a variety of alternative pathways as well.