Suppression

Proline

Category: Natural chemicals

Type

Voluntary

Introduction and description

All photos by Brent McGregor

Proline is an α-amino acid, one of the twenty main amino acids.   It is classified as ‘non-essential’, because the human body can make it out of other inputs, but yet again we find this classification unhelpful, it is essential and it might be better to eat it, rather than rely in this process to produce it.

To show you just how long and convoluted the process of making proline out of other inputs is we have used the description from Wikipedia, word for word....

Proline is biosynthetically derived from the amino acid L-glutamate. Glutamate-5-semialdehyde is first formed by glutamate 5-kinase (ATP-dependent) and glutamate-5-semialdehyde dehydrogenase (which requires NADH or NADPH). This can then either spontaneously cyclize to form 1-pyrroline-5-carboxylic acid, which is reduced to proline by pyrroline-5-carboxylate reductase (using NADH or NADPH), or turned into ornithine by ornithine aminotransferase, followed by cyclisation by ornithine cyclodeaminase to form proline.

Personally I’d rather have a tuna sandwich.

Another Wikipedia quote:

The distinctive cyclic structure of proline's side chain gives proline an exceptional conformational rigidity compared to other amino acids. It also affects the rate of peptide bond formation between proline and other amino acids. When proline is bound as an amide in a peptide bond, its nitrogen is not bound to any hydrogen, meaning it cannot act as a hydrogen bond donor, but can be a hydrogen bond acceptor.”

What does this mean?  Proline is used as one of the raw materials in forming collagen and we use collagen all over our bodies to form the structural basis for skin, muscles, eyes, tendons, ligaments and so on.  The heart is a muscle, the intestines have a muscular foundation, even the uterus has muscles and the penis of course does.  So since collagen is rather key in our performing a whole host of important functions, so is proline.

Collagen has an unusual amino acid composition and sequence:

  • Glycine is found at almost every third residue.
  • Proline makes up about 17% of collagen.

Collagen contains two uncommon derivative amino acids not directly inserted during translation. These amino acids are found at specific locations relative to glycine and are modified post-translationally by different enzymes, both of which require vitamin C as a cofactor.

  • Hydroxyproline is derived from proline
  • Hydroxylysine is derived from lysine - depending on the type of collagen, varying numbers of hydroxylysines are glycosylated (mostly having disaccharides attached).

So again, to make collagen we need proline, glycine, Vitamin C and lysine.  That is how important proline is. 

Here a chemist explains in simple terms some extra information [I jest].

The exceptional conformational rigidity of proline affects the secondary structure of proteins near a proline residue and may account for proline's higher prevalence in the proteins of thermophilic organisms. Protein secondary structure can be described in terms of the dihedral angles φ, ψ and ω of the protein backbone. The cyclic structure of proline's side chain locks the angle φ at approximately −60°.

Thermophile means ‘heat-loving’, and organisms that are thermophilic like an optimum growth temperature of 50 °C or more, a maximum of up to 70 °C or more, and a minimum of about 40 °C. So proline is used a lot as a raw material in other organisms besides us.  The list of foods show that prolines are in warm blooded animals and cold blooded fish, so it is almost an essential building block on which creatures of all sorts have been made/designed.

I had to put the following in, I’ve no idea what it means, it has a sort of poetry about it, a Wikipedia chemist waxes lyrical

Proline acts as a structural disruptor in the middle of regular secondary structure elements such as alpha helices and beta sheets; however, proline is commonly found as the first residue of an alpha helix and also in the edge strands of beta sheets. Proline is also commonly found in turns (another kind of secondary structure), and aids in the formation of beta turns. This may account for the curious fact [!!] that proline is usually solvent-exposed, despite having a completely aliphatic side chain.

Wow!! Back to practicalities.

You will notice above that Vitamin C is an essential part of the process to make collagen. 

…. the hydroxylation of proline is a critical biochemical process for maintaining the connective tissue of higher organisms. Severe diseases such as scurvy can result from defects in this hydroxylation, e.g., mutations in the enzyme prolyl hydroxylase or lack of the necessary ascorbate (vitamin C) cofactor.

To put this simply, proline alone is not enough, you need Vitamin C as well.

In brewing, proteins rich in proline combine with polyphenols to produce haze, so a cloudy beer is not necessarily a bad beer [unless it is caused by dead yeast which hasn’t been filtered properly].

Sources of proline in Food

 

We have provided an observation derived from Dr Duke’s phytochemical database that shows the plants that have proline.  The table below shows the other foods and is ordered by nutrient content.  It comes from the USDA Nutrients database, which produces a list some 30 pages long and which also has a fair amount of repetition, caused by the fact that each product has to have labelling whereas we are looking for broad guidelines we can use in cooking and preparing balanced meals. 

It also includes processed food, which we have excluded – eg Cheese spread, pasteurized process, American. 

We have included no vegetables generally, as these are in Dr Duke’s list, we have kept things like beans and sweetcorn in for comparison.  There are likely to be some disparities in content [not too reat] between Dr Duke and this list simply because the source of the food will be different.

Overall in order to get adequate proline input, a vegetarian needs to concentrate on the dairy products and cheese.  A meat eater has a very easy time, unless of course they have become allergic to gelatine.  In this case, they might be better to go vegetarian.

Description

Proline (g)
Value Per

Cheese - hard and soft cheeses especially full fat whole milk cheese eg swiss, parmesan, provolone, mozzarella, muenster, cheddar, camembert, blue, cottage cheese [full fat], feta [full fat], ricotta, Neufchatel, cream cheese,

various

Milk and dairy products – full fat, including buttermilk, condensed [unsweetened] and evaporated, and also yoghurt [full fat], cream and sour cream, butter

3.50 and various

Seeds – mustard sesame , safflower, pumpkin, lotus, sunflower, caraway

2.29 and various

Game meat – various including  bison, deer, elk, with fat

various

Beef – various cuts including  brisket, shank, loin, steak, ground/minced, loin, tenderloin, etc with fat

1.60

Turkey – meat and skin, especially but not exclusively the dark meat

1.58

Pasta - Macaroni, spaghetti, egg noodles, Japanese noodles, etc preferably but not exclusively wholegrain.  Can be fresh or dried

1.57

Fish roe 

1.52

Pork and ham – various cuts including ground/minced  with fat, or joints and whole meat sausages

1.50

Wheat flour

1.41

Chicken – meat and skin

1.37

Veal – all cuts eg  shank, breast with fat

1.32

Barley flour or meal

1.25

Lamb -  various cuts eg  shoulder, leg

1.24

Spices -  curry powder [unspecified content]

1.24

Nuts -  butternuts, almonds, ‘mixed nuts’ [unspecified content], almond butter, hazelnuts

1.24

Peanuts and peanut butter

1.19

Fish -  mostly the oily fish such as yellowtail , tuna, salmon [pink, fresh or canned, wild or farmed], trout, bluefish, grouper, burbot, pike, scup, swordfish, mackerel, ling, sea trout, tilapia, bluefish , haddock, perch, herring, wolfish/monkfish, flounder, sole, cod,

1.05 and various

Beans – various including  black, pink, adzuki, turtle,

0.92

Crustaceans -  spiny lobster, queen crab

0.87

Tofu -  raw, firm and soft

0.85

Guinea fowl

0.85

Squab -  (pigeon), meat and skin

0.84

Cornmeal, whole-grain and cornflour - masa

0.71

Sorghum flour, whole-grain

0.65

Mollusks -  octopus, mussels, oysters

0.61 and various

Soybeans

0.61

Edamame

0.60

Eggs

0.56

Turmeric

0.48

Cinnamon

0.42

Sweetcorn [kernels cut off cob] 

0.37

Rice flour, brown

0.34

Coffee

0.34

Rice -  white, long-grain

0.34

Ginger [dried]

0.33

Dried fruits – Apricots, peaches

0.29

Coconut

0.28

Dill -  fresh

0.25

Bamboo shoots

0.22

Mushrooms, portabella

0.12

 

 

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