Nutrition- Riboflavin (Vitamin B2)

Front 1

What is riboflavin made up of?

Back 1

Riboflavin is made up of:

Flavin (Isoalloxazinering) with a

Ribitol (sugar alcohol) side chain attached.

Front 2

Inside the cells, how is flavin found?

Back 2

In biological systems (inside the cells), riboflavin is usually phosphorylated to form:

Flavin mononucleotide (FMN) (Riboflavin + 1 phosphate) and

Flavin adenine dinucleotide (FAD) (Riboflavin + pyrophosphate + adenine nucleotide).

Front 3

What is the stability of riboflavin like?

Back 3

It is stable to heat, but very sensitive to light destruction.

Front 4

What is a good source of riboflavin?

Back 4

Milk is a good source of riboflavin, and is normally stored in opaque containers to prevent exposure to light.

Riboflavin is widely distributed in foods,although more so in those of animal origin.

Front 5

How is riboflavin found in food?

Back 5

Riboflavin is found mostly bound to proteins in foods and it must be digested (freed from flavoproteins) in order to be absorbed.

Front 6

Where is free riboflavin absorbed primarily and how so?

Back 6

Free riboflavin is absorbed primarily in the proximal portion of the small intestine

By a saturable, energy dependent, sodium independent carrier named riboflavin transporter 2 (RFT2).

Front 7

How is riboflavin absorbed if it is in a high amount in the intestinal lumen?

Back 7

When highly abundant in the lumen of the intestine, riboflavin may also be absorbed by diffusion into the enterocyte.

Front 8

What inhibits riboflavin absorption?

Back 8

Alcohol

Front 9

What is proportion of riboflavin in the blood?

Back 9

The proportion in the blood is:

Riboflavin(50%)

FAD (40%)

FMN (10%)

Front 10

How are these forms of riboflavin transported in the blood?

What is the main transport protein?

Back 10

They are transported by a variety of proteins including albumin, fibrinogen and globulin (mainly immunoglobulin).

Albumin is the main transport protein.

Front 11

How does riboflavin cross the cell membrane?

Back 11

Regardless of the form in which the vitamin reaches the tissues, free riboflavin, not FAD or FMN is the form that crosses cell membranes and does so through a carrier-mediated process involving a riboflavin-binding protein.

Front 12

What organs has the most riboflavin?

Back 12

Liver, kidneys and heart are the organs with the highest concentration of riboflavin – not surprising because they have high metabolic rates.

Front 13

How long can riboflavin help with metabolic demands?

Back 13

It has been estimated that the total body reserve of riboflavin in the adult human is sufficient to provide for the metabolic demands for 2-6 weeks.

Front 14

What happens once riboflavin enters the cell?

Back 14

Once inside the cells,riboflavin is converted into its coenzyme forms:

Riboflavin --> FAD -using FAD synthetase enzyme

Riboflavin--> FMN - using flavokinase enzyme

Front 15

What does FMN and FAD do in the cell?

Back 15

FMN and FAD function as prosthetic groups (tightly bound, specific non-polypeptide compound required for the biological function of some proteins) for enzymes called flavoproteins that are involved in oxidation-reduction reactions.

Front 16

What is special about flavoproteins?

Back 16

Flavoproteins show great versatility in accepting and transferring one or two electrons with a range of potentials.

Flavoproteins can be reduced and or oxidized.

Therefore, they play a wide variety of roles in intermediary metabolism.

Front 17

What are the primary functions of riboflavin?

Back 17

Requiredas a coenzyme for carbohydrate and fat metabolism.

Front 18

What are the symptoms of deficiency of riboflavin?

What are the symptoms of toxicity of riboflavin?

Back 18

Ariboflavinosis (lack of riboflavin), swollen mouth and throat, seborrheic dermatitis, anemia.

None known.