Protein Modifications

Oxidative stress involves protein modification that occurs either by direct reaction with

ROS or indirectly by reaction with secondary by-products of oxidative stress. Among the fi ».

numerous agents that cause protein oxidation are ROS/RNS (H202, , HOC1, ONOO-), reduced transition metals (Cu, Fe), and the by-products of lipid and free amino acid oxidation. Oxidizing species directly attack the Cys and Met residues. Metals generally chelate with histidine, while Lys, Arg, Pro, and Thr form carbonyl groups on side chains. Indirect protein oxidation occurs with lipid peroxidation breakdown products such as 4-HNE and MDA, which add to Lys, His, and Cys residues.

As there are several mechanisms of oxidizing the various amino acyl side chains, there can be numerous different types of protein oxidative modifications. And because proteins have many different functions, oxidative modifications can lead to a range of functional consequences. Oxidation of the aminocarboxyl generates a carbonyl; other oxidative modifications include formation of protein HNE adducts, nitrated tyrosine residues and glycated end products. Modification of structural proteins or enzymes can lead to a loss of function. Modifications in proteins involved in signal pathways that regulate proliferation, angiogenesis, and apoptosis also occur and often correlate with progression of disease.29'65 DNA -repair enzymes, when damaged, cause insufficient DNA repair. Apart from DNA-repair enzymes, p53 is reported to be posttranslationally modified after exposure to NO and its derivatives. The p53 protein mediates single-strand DNA annealing. The binding of p53 to DNA regulates cellular functions, such as gene transcription, DNA synthesis and repair, cell cycle arrest, apoptosis, and senescence.66-68 Modifications in the p53 protein therefore affect these functions, contributing to the molecular pathogenesis of cancer.

Aloe and Your Health

Aloe and Your Health

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