Protein, amino acid turnover inhibition

Glyphosate is phloem mobile and accumulates in accordance with source-sink relationships in meristematic areas of the treated plants. " The general physiological effects of glyphosate are consistent with its acting as a metabolic poison. Death is a slow process, requiring days or weeks much more rapid effects, within hours, can be demonstrated at the biochemical level. These effects can be explained if the turnover rates of specific proteins, and therefore sensitivity to amino acid synthesis inhibition, differ. Inhibition of phenolic biosynthesis and chlorophyll formation and effects on the levels of the phytohormone 3-indoleacetic acid have been considered as target sites but can be viewed as necessary consequences of the primary interference with aromatic amino acid biosynthesis. " ... 

Recent approach utilise isolated PSII complexes as biomediators. The PSII reaaion center was isolated in 1987 and the isolated complex was found to maintain its herbicide-binding ability. The binding affinity of the herbicide depends on the amino acid composition of the hydrophilic loop in the D1 protein. It is recognized that these herbicides act by binding D1 protein of reaction center. Two levels of action occun displacement of the secondary quinone electron transfer PQ and inhibition of D1 protein turnover. ... 

Although cortisone interferes with protein synthesis in peripheral tissue, the hormone stimulates protein synthesis in liver. The increased rate of protein synthesis results from an effect of the hormone on the penetration of the amino acid through the cell membrane. The effects of the steroid hormones on the amino acid penetration were demonstrated with the aid of a-aminoisobutyric acid, a nonmetabolizable amino acid the intracellular penetration of which is regulated by mechanisms similar to those controlling glycine penetration. The penetration of a-aminoisobu-tyric acid is competitively inhibited by valine. Two hours after the injection of cortisol, the aminoisobu-tyric acid content of the liver is increased 70%. The increase in amino acid uptake may explain the increase of protein synthesis in liver observed early after cortisone injection. In that connection, it is of interest that an accelerated turnover of serum albumin has been reported early after the injection of cortisone. Since the concentrations in the levels of the blood protein are not changed, it seems that increased synthesis only compensates for increased catabolism. 

Progress has been made in demonstrating synthesis of specific proteins by cell-free systems, e.g., on the synthesis of cytochrome c by isolated rat liver mitochondria (S3, cf. 383) and on the synthesis of serum albumin by the isolated microsome fraction of rat liver 34, cf. 335,336). Campbell et al. 34) concluded that while specific serum albumin is, indeed, synthesized on the ribonucleoprotein particle fraction of the microsomes, it is not readily released in soluble form. In other words, the isolated microsomes have lost their ability to promote substrate turnover. The same is true for the hemoglobin-synthesizing RNP particles from rabbit reticulocytes 35, cf. 138). Ogata and associates 36) have essentially confirmed the results of Campbell et al. 34) on the synthesis of serum albumin by liver microsomes they have also studied the relative effect of both stimulatory and inhibitory factors on the incorporation of different amino acids into total ribonucleoprotein and into serum albumin, and showed that the requirements for the two processes were generally the same it may be noted, however, that pretreatment of the pH 5 enzymes with ribonuclease, which caused a 95% inhibition of the ineorporation into ribonucleoprotein, inhibited the corresponding incorporation into serum albumin by only 55%. 

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