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How knowing your left from right can bulk up shellfish

Scientists from Evonik Industries and the University of Reading have used STFC's ISIS Neutron and Muon Source to study the difference between two forms of a new feed supplement for shellfish that is more sustainable and nutritious.

The study increases understanding of why this commercially important material has these benefits and how this could be applied to other feeding techniques. These new findings open the doors on one way to potentially get greater food yields when farming shellfish in the future.

Do you get your left and right mixed up? So does biochemistry!

Amino acids are the essential building blocks of important biological structures in our bodies, like our muscles, and can have different forms depending on their chemical structure. Within each amino acid, there is a carbon atom around which the other atoms in the amino acid are bonded in a clockwise or anticlockwise order - this atom is known as a chiral centre after the ancient Greek cheir meaning ‘hand.’

As ‘handedness’ is the general term for describing objects with this property, you could also describe the amino acid forms as being left or right ‘handed.’ Each amino acid form is a reflection of the other, the same as your right and left hand, so would not align if placed over each other.

Giving shellfish a hand

Methionine is one of these essential amino acids and is widely used in aquafarming to bulk up slow feeders, like prawns and shrimps, to promote better fish health and develop tastier shellfish for us. Unfortunately, if methionine is given as feed, the shellfish gain little weight from it because most of it is either excreted or used for energy.

Even worse, it is highly water soluble so dissolves in the water before it can reach the fish and can also disrupt ecosystems by encouraging the excessive growth of algae – a process known as eutrophication.

To solve this, the shellfish were not enrolled at the local gym but Evonik Nutrition & Care GmbH did develop methionyl-methionine, a new alternative supplement formed of the original amino acid bonded to another methionine. This feed supplement contains the left-handed and right-handed form of methionine so can be digested and used to build proteins, and is also more sustainable as it has a lower water solubility.

To further muddy the waters, methionyl-methionine contains two chiral centres, and so it can exist as four different forms: left-left, left-right, right-right and right-left. To dive a bit deeper, the study used various techniques to look at crystals of the methionyl-methionine used in the Evonik feed supplement.

Diving deeper

One of the techniques used was inelastic neutron scattering (INS) on the TOSCA spectrometer at the ISIS Neutron and Muon Source (ISIS) to build a fuller picture of the crystal’s structures. INS uses neutrons (particles with no electric charge) to examine the movement and structure of the crystals without damaging the sample.

When the neutrons interact with the sample, scattering occurs and by measuring the energy difference between the incoming and outgoing neutrons, information about the crystal’s left-handed or right-handed form can be obtained at a small scale.

Right around the corner from ISIS, the scientists were also able to use facilities in the Research Complex at Harwell, as well as STFC’s computing resources, to study the crystals. In combination with electron microscopy and other vibrational spectroscopy techniques, the scientists were able to study the differences between the methionyl-methionine forms.

Underpinning this spectroscopic and microscopy work at STFC, scientists at the University of Reading used both single-crystal and powder X-ray diffraction to determine two new methionyl-methionine crystal structures.

Aside from differences in the shape and structure of the forms, they found that two of the forms showed very different solubilities which is important for knowing how to give the shellfish the feed supplement underwater. They also found no interaction between the two forms in a sample containing an equal mixture of them both at a small microscopic scale and a larger visible scale.

When the methionyl-methionine feed supplement is synthesised industrially, the different forms are likely to be in a mixture so insights like this could alter costs in the synthesis process. The insights from this study could lead to future research on the solubility differences between the forms and how this could be applied to other feeding techniques or feed supplements.

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Last updated: 16 March 2021


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