Threonine, Thr

It is a peptide containing 27 amino acid residues containing the amino acids L-histidine (His) L-aspartic acid (Asp) L-serine (Ser) glycine (Gly) L-threonine (Thr) L-phenyl-alanine (Phe) L-glutamic acid (Glu) L-glutamine [Glu(NHj)] L-leucine (Leu) L-arginine (Arg) L-alanine (Ala) and L-valinamide (Va -NHj). 

In addition, eNOS is subject to protein phosphorylation. It can be phosphotylated on several serine (Ser), threonine (Thr), and tyrosine (Tyr) residues however, major changes in enzyme function have been reported for the phosphorylation of amino acid residues Seri 177 and Thr495 (in the human eNOS sequence) (Fig. 3). 

Copolymers of a-hydroxy acids and a-amino acids are one type of poly(ester-amide)s and are called polydepsipeptides (PDPs) [17]. Since some of natural occurring a-amino acids, typically Asp, Glu, lysine (Lys), cysteine (Cys), serine (Ser), and threonine (Thr), possess reactive (hydrophilic) side-chain groups, PDPs... 

PS II absorbs more light than PS I. As such PS I cannot take electrons as fast as PS II can supply, leaving plastoquinone in its reduced state. This reduced plastoquinone activates a protein kinase that phosphorylates the threonine (Thr) residue of the LHCs that in turn migrate to the unstacked portion of the thylakoid membrane where it binds to PS I. As a result, a large portion of incident light is funneled to PS I. 

Threonine (Thr or T) ((2S,31( )-2-amino-3-hydroxybutanoic acid) has an aliphatic hydroxyl side chain and is classified as a polar, uncharged amino acid with the formula HOOCCH(NH2)CHOHCH3. Together with Ser and Tyr, Thr is one of the three proteinogenic amino acids bearing an alcohol group. Thr can be seen as a hydroxylated version of Val. With two chiral centers, Thr can exist in four possible stereoisomers, or two possible diastereomers of L-Thr. However, the name L-Thr is used for one single enantiomer, (2S, 3if)-2-amino-3-hydroxybutanoic acid. The second diastereomer (2S,3S), which is rarely present in nature, is called L- //o-Thr. 

Figure 9-3. Fates of the carbon skeletons upon metabolism of the amino acids. Points of entry at various steps of the tricarboxylic acid (TCA) cycle, glycolysis and gluconeogenesis are shown for the carbons skeletons of the amino acids. Note the multiple fates of the glucogenic amino acids glycine (Gly), serine (Ser), and threonine (Thr) as well as the combined glucogenic and ketogenic amino acids phenylalanine (Phe), tryptophan (Trp), and tyrosine (Tyr). Ala, alanine Cys, cysteine lie, isoleucine Leu, leucine Lys, lysine Asn, asparagine Asp, aspartate Arg, arginine His, histidine Glu, glutamate Gin, glutamine Pro, proline Val, valine Met, methionine.

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