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Catabolism of proteins and amino acid nitrogen
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Catabolism of proteins and amino acid nitrogen Protein turnover occurs in all forms of life - Amount of nitrogen relatively constant except growth - No storage form of nitrogen reserve muscle i... s NOT for storage - Turnover 1 – 2% of total body protein (principally muscle protein) - High rates of protein degradation (undergoing structural rearrangement – chemically altered): Uterine tissue during pregnancy Skeletal muscle in starvation Tadpole tail tissue during metamorphosis (I will give everyone a hundred pesos if this is mentioned in the exam) - 75% of liberated aa: reutilized - 20 – 25%: rapidly degraded (not stored) o Carbon skeletons amphibolic intermediates o Amino nitrogen urea excreted in urine Proteases and peptidases degrade proteins to amino acids Half life (t1/2) – relative susceptibility of a protein to degradation - Time required to lower its concentration to half the initial value o Housekeeping enzymes (typical) – over 100h o Key regulatory enzymes – 0.5 – 2h PEST sequences – regions rich in proline, glutamate, serine, threonine which target some proteins for rapid degradation Intracellular proteases – hydrolyze internal peptide bonds Endopeptidases – cleave internal peptide bonds of peptides which are then degraded to Aminopeptidases – remove amino acids sequentially from amino terminals Carboxypeptidases – remove amino acids sequentially from carboxyl terminals [Show More]
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