Tryptophan Synthetase A 279

Tryptophan synthetase A

Here is the amino acid sequence in just one protein in your body. We have written the formula for this protein from left to right. Each unit is integrally connected to the next, as shown below without spaces between amino acids. But, if they were separated, the sequence would read like this: Methionyi, glutaminylarginyl, tyr-osyl, glutaminyl, etc.

Methionylglutaminylarginyltyrosylgtutamyl-serylle ucylphenyla I any lalari y Iglu taminy 11 eucyl-lysylglutamylarginyllysyglutamylglycylalanyl-phenylalanylvalylprolylphenylalanylvalyl-threonylleucylglycylaspartylprolylglycyl-isoleucy Igl utamy l g lutam i ny isery I leucy I fysyl-isoteucylaspartythreonylleucylisoleucyl-glutamyialanylglycylalanylaspartylalanylleucyl-glutamylleucylg iycy lisoleucy I prolylphe nylalanyl-serylaspartylprolylleucylalanylaspartylglycyl-prolylthreonylisoleucylglutaminylasparaginyl-alanyltiireonylleucylarginylalanylphenyl-alanylalanylalanylglycyh/alylthreonyfprolyl-alanylglutaminylcysteinylphenylalanylglutamyl-methionylmethionylleucylalanylleucylisoleucyl-arginylglutaminyllysylhistidylprolylthreonyl-isoleucy I proly lisoleucylglycy I leucy I leu cyl~ methionyltyrosylalanylasparaginylleucylvalyl-

phenylalanylasparaginyllysylglycyiisoleucyt-aspartylglutamylpheriylalanyltyrosylalanyl-glutaminylcysteinylglutamyllysylvalylglycylvalyl-aspartylserylvalylleucylvalylalanylaspartyl-valyl prolyl valylglutaminylglutamylseryl-alanyproiylphenylalanylarginylglutaminylalanyl-alanylleucylarginylhistidylasparaginylvalyl-alanylprolylisoleucyfphenylalanylisoleucyl-cystei nylpro ly I profylas party la I any I aspa rty I-aspartylaspartylíeucylleucylarginylgJutaminyl-Isoleücylalanylseryltyrosylglycylarginylglycyl-tyrosylthreonyltyrosylleucylleucylserylarginyl-alanylglycylvalylthreonylglycylalariylglutamyl-asparaginylarginylalanylalanylleucylprolylleucyl-asparaginyihaistidylleucyivalylalanyllysylleucyl-

lysylglutamyltyrosylasparaginylalanylalanyl-protylprolylleucylglutaminylgtycylphenylalanyl-glycylisoleucylerylalanylproJylaspartyl-glutaminylvalyllysylalanylalanylisoleucyl-aspartylalanylglycylalanlafanylglycylalanyl-isoleutylseryglycylseryîalanylisoleucylvalyl-lysylisoleucylisoleucylglutamylglutaminyl-histidylasparaginylisoleucylglutamyfprolyl-glutamyllysylmethionyîleucylalancylalanyl-leucyllysylvalylphenylalanylvalylglutamiriyl-prolylethionyllysylalanylalthreonylarginyl-serine,

Here are all 39 forms. What a hodgepodge for the random accidents of evolution to sort through—and come up with only the L forms. Each one has its own complicated sequence of amino acids:

1 - Glycine

2a - L-Alanine

3a - L-Valine 4a - L-Leucine 5a - L-Isoleucine 6a - L-Serine 7a - L-Threonine 8a - L-Cysteine 9a - L-Cystine 10a - L-Methionine 11a - L-Glutamic Acid 12a - L-Aspartic Acid 13a - L-Lysine 14a - L-Arginine 15a - L-Histidine 16a - L-Phenylalanine 17a - L-Tyrosine 18a - L-Tryptophan 19a - L-Proline 20a - L-Hydroxyproline

2b - D-Alanine 3b - D-Valine 4b - D-Leucine 5b - D-Isoleucine 6b - D-Serine 7b - D-Threonine 8b - D-Cysteine 9b - D-Cystine 10b - D-Methionine 11b - D-Glutamic Acid 12b - D-Aspartic Acid 13b - D-Lysine 14b - D-Arginine 15b - D-Histidine 16b - D-Phenylalanine 17b - D-Tyrosine 18b - D-Tryptophan 19b - D-Proline 20b - D-Hydroxyproline

WHY ONLY THE L FORM—You might wonder why the D form of protein would not work equally well in humans and animals. The problem is that a single strand of protein, once it is constructed by other proteins (yes, the complicated structure of each protein is constructed in your body cells by other brainless proteins!), it immediately folds into a certain pattern. If there was even one right-handed amino acid in each lengthy string, it could not fold properly.

(See our special study on Protein on our website. It is fabulous, and shows the astoundingly complex activities of proteins inside the cell.)

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