Among the indispensable amino acids, lysine is most strongly conserved and is less rapidly catabolised.[11] Proteins of high biological value invariably have high lysine content. Most of the several essential functions of the lysine residue in cell and body proteins are largely related to its e-amino group. The positively charged lysine residue execute several important functions in protein like;[10]
Receptor affinity: Lysine-rich regions in LDL particles are essential for their “docking” at hepatic LDL receptors.
Endoplasmic reticulum retention: Mammalian cytoplasmic proteins at fresh synthesis have Specific lysine-containing motifs present at carboxyl groups which act as identifying tags allowing them to be retained in the endoplasmic reticulum.
Muscle function: Titin is a large sized muscle protein which appears to control elasticity of different types of muscle. At its center, it contains a lysine-rich motif termed PEVK (abbreviated for proline, glutamate, valine, and lysine) which is believed to provide it the required elasticity acting as a “spring”.
It has a tendency to be stored in muscle tissues where it may act as a binding agent besides playing an important role in collagen formation and wound healing.[12]
Lysine competes with other dibasic amino acids like arginine and ornithine for transportation not only in intestinal mucosa and renal tubule but also in mitochondria.[11] It antagonizes arginine by way of the following five mechanisms. Lysine functions as an antimetabolite of arginine. Lysine competes with arginine for reabsorption in the renal tubules thereby increasing arginine excretion in urine. Lysine also competes with arginine for transport into cells and at absorption sites in the intestines. If there is excess concentration of lysine in the gut, then absorption of arginine is decreased. Lastly, lysine induces enzyme arginiase, which degrades arginine.[13]
Excess lysine in rats has been shown to inhibit liver arginase activity. A study with of 0.5 mmol/kg intravenous infusion of L-lysine monohydrochloride caused an increase in plasma concentration of arginine with its increased leakage in urine which was inferred to be due to inhibitory effect of lysine on arginine activity.[11] This allows lysine to control growth of herpes simplex virus which exploits the growth-promoting action of arginine.[14] The competing nature of lysine against arginine and ornithine was also shown to interfere with the ammonia cycle and could lead to an increase in urinary ammonia.
Infusion of lysine with a dosage of 0.4 g/kg did not show blood pressure reduction or increase in extracellular fluid volume which are primarily markers of vasodilatation necessary for use against cardiovascular diseases, however, it did lead to an increase in plasma cyclic GMP as well as effected plasma electrolytes and atrial natriuretic peptide concentrations positively. It has also been shown to reduce stress by blocking the stress receptors and improving the cardio vascular response in general.[15]
L-lysine HCl injection has been reported to induce kaliuresis, i.e. elimination of significant amount of potassium in urine, when injected at a pH of 7.4. It is believed to achieve this by extracellular acidosis and intracellular alkalosis, thereby suppressing the kidney’s ability to secrete H+ ion and facilitating K+ secretion.[16]
L-lysine HCl has demonstrated effective use against herpes simplex virus. It has also been used prophylactically against the virus.[17]
Patients suffering from lysinuric protein intolerance suffer from poor physical development and other issues like hepatosplenomegaly, muscle weakness and osteoporosis due to their inability to absorb protein. Oral ingestion of lysine in these patients interferes strongly with their ammonia cycle. However, the intravenous pathway for infusion of lysine has been shown to be well tolerated and not interfere in the ammonia cycle of such patients unlike oral ingestion which leads to hyperammonemia due to absence of arginine and ornithine.[18]