Structure of Biopolymers/Interaction of Riboflavin with Aminoacids/Protein

Abstract

The combination of Flavin coenzyme with protein leads to a shift of absorption maxim of protein, and quenching of riboflavin intensity. The binding of riboflavin with tryptophan has been studied by several workers. This binding is Important regarding the combination of Flavin (coenzyme) with protein (apoenzyme). Tryptophan is also found in protein bound and free from, hence the binding of 1. Riboflavin, a vitamin is highly sensitive to light and is destroyed by it, the binding of riboflavin with tryptophan Can preserve it against the destructive effect of light. 2. Tryptophan, an essential aminoacid is the precursor of serotine, which is found in brain in bound form with riboflavin. 3. Changes in tryptophan cancentration in plasma and other tissues of rats and human alter the serotonin concentrations in brain too. 4. Various drugs when injected to rats have been found to alter tryptophan concentration in various organs 5. The injection of drugs in this way may alter serotonin concentration through tryptophan pathway and explains The pharmacological behaviour of these drugs. The work was investigated in two phases: A. Interaction of riboflavin with aminoacids. B. Interaction of tryptophan with proteins.

A. Interaction of Flavin with aminoacids. Interaction of Flavin with aminoacids was studied in detail. Only tryptophan tyrosine and phenyalanine were Found to form complexes with riboflavin and the extent of interaction is of the order tryptophan, tyrosine, phenylalanine. The extent of interaction was correlated with electron donating power of these aminoacids. Quenching of riboflavin flourscence by these aminoacids was also noticed. Interaction is studied at various pH values and neutral complexes are found to be most stable. Complex formation was found to be enhanced in presence of light. This finding is suggested to be valueable in regard of the electron transfer behaviour of the reaction. The binding of riboflavin with tryptophan can preserve it against destructive effect of light.

B. Interaction of tryptophan with protein. 1. Tryptophan is the only aminoacid bounded to plasma proteins, the albumin. The concentration of free and protein bound tryptophan was estimated in the plasma of Uromastix hardwickii during hibernation and without hibernation. The data obtained in two periods were correlated with the mode of life of this animal. 2. The concentration of free and protein bound tryoptophan was also determined in the plasma of various species belonging to 3 phyla of animal kingdom. The degree of tryptophan binding was shown to be an evolutionary feature. 3. The concentration of free and bound tryptophan was estimated in the plasma, liver and brain of Uromastix hardwickii (lizard) before and after the intraperitoneal administration of sodium salicylate (drug). Injection of the drug was found to enhance free tryptophan concentration; also the animal became slightly active.The pharmacological action of the drug has been correlated with the increase in free tryptophan concentration. It is a preliminary step to examine the neuro-pharmacological behaviour pf salicylate. In this regards it will be important to determine actual serotonin concentration after administration of the drug. The nero-pharmacological behaviour of other drugs like tetracyclines, phenothiazines, saccharin, and pencillin may be investigated in a similar way. 4. The binding of L-tryptohan with human serum albumin (HAS) was also investigated. The results indicate that there are two binding sites in albumin. Primary site gets saturated than the molarity of tryptophan in the reaction mixture is 10 times greater than the molarity of albumin. One molecule of tryptophan is bounded/molecule of albumin at the primary site. Interactions of salicylate with albumin was also studied. Number of molecules bounded/ mole of albumin is always same, but binding constant varies for tryptophan and saliculate. One more aminoacid tyrosine which resembles structurally with salicylate was also found to bind with HAS but the binding constant in this case was very less. INTERACTION OF RIBOFLAVIN WITH TRYPTOHAN AND PROTEINS The combination of Flavin coenzyme with protein leads to a shift of absorption maxima of protein, and quenching of riboflavin intensity. The binding of riboflavin with tryptophan has been studied by several workers. This binding is important regarding the combination of Flavin (coenzyme) with protein (Apoenzyme). Tryptophan is also found in protein bound and free form, hence the binding of; 1. Riboflavin with tryptophan 2. Tryptophan with protein Is important keeping the following points in mind. 1. Riboflavin a vitamin is highly sensitive to light and is destroyed by it, the binding riboflavin with tryptophan can preserve it against the destructive effect of light. 2. Tryptophan, an essential amino acid is the precursor of serotonin, which is found in brain in bound form with riboflavin 3. Changes in tryptophan concentration in plasma and other tissues of rats and human alter the serotonin concentrations in brain too. 4. Various drugs when injected to rats have been found to alter tryptophan concentrations in various organs. 5. The injection of drugs in this way may alter serotonin concentration through tryptophan pathway and explains the pharmacological behaviour of these drugs.