Objective — to study the content of amino acids noncovalent bound with placental cytoplasmic proteins in placenta in physiological pregnancy and placental insufficiency in order to clarify molecular mechanisms of the development of this obstetrical pathology. Material and methods. Fifty seven women were examined, including 30 women with pregnancy complicated by placental insufficiency, and 27 women without complications. Placental cytoplasmic proteins were isolated by differential ultracentrifugation, and after a multi-step treatment with saline solutions, a fraction of loosely bound amino acids, as well as a fraction of free amino acids were released. The quantitative measurement of amino acids was performed on an automated chromatograph. Results. In case of placental insufficiency, bidirectional changes in the content of the bound forms of amino acids and their ratio with free amino acids were revealed in the placenta. There are pronounced deviations of hydrophilic charged amino acids, which to a great extent maintain electrostatic interactions in the protein molecule. The changes in the quantity of hydrophobic bound amino acids in placental insufficiency are reflected on the level of hydrogen bonds stabilizing the protein secondary structure under physiological conditions. The reduction of the bound form of cysteine also has an adverse impact on protein structures and leads to the modification of intraprotein disulfide bonds. Conclusion. The found changes in the balance of the bound forms of amino acids in connection with their impact on the structure and properties of placental cytoplasmic proteins are, probably, important links in the whole chain of molecular and biochemical disturbances in placental insufficiency.