The organization of the modules necessary to biosynthesize Vancomycin is shown in Figure 1. In the biosynthesis of Vancomycin, additional modification domains are present, such as the epimerization (E) domain, which isomerizes the amino acid from one stereochemistry to another, and a thioesterase domain (TE) is used as a catalyst for cyclization and releases of the molecule via a thioesterase scission. A set of NRPS enzymes (peptide synthase VpsA, VpsB, and VpsC) are responsible for assembling the heptapeptide. (Figure 2). VpsA codes for modules 1, 2, and 3. VpsB codes for modules 4, 5, and 6, and VpsC codes for module 7. The vancomycin aglycone contains 4 D-amino acids, although the NRPSs only contain 3 epimerization domains. The origin of D-Leu at residue 1 is not known. The three peptide syntheses are located at the start of the region of the bacterial genome linked with antibiotic biosynthesis, and span 27 kb.β-hydroxytyrosine (β-HT) is synthesized prior to incorporation into the heptapeptide backbone. L-tyrosine is activated and loaded on the NRPS VpsD, hydroxylated by OxyD, and released by the thioesterase Vhp. The timing of the chlorination by halogenase VhaA during biosynthesis is currently undetermined, but is proposed to occur before the complete assembly of the heptapeptide.After the linear heptapeptide molecule is synthesized, vancomycin has to undergo further modifications, such as oxidative cross-linking and glycosylation, in trans by distinct enzymes, referred to as tailoring enzymes, to become biologically active (Figure 3). To convert the linear heptapeptide to cross-linked, glycosylated vancomycin, six enzymes, are required.
This cycle may be repeated several times a week or, in more serious cases, several times a day and may directly cause:

Chronic gastric reflux after eating, secondary to vomiting
Dehydration and hypokalemia due to renal potassium loss in the presence of alkalosis and frequent vomiting
Electrolyte imbalance, which can lead to abnormal heart rhythms, cardiac arrest, and even death
Esophagitis, or inflammation of the esophagus
Mallory-Weiss tears
Boerhaave syndrome, a rupture in the esophageal wall due to vomiting
Oral trauma, in which repetitive insertion of fingers or other objects causes lacerations to the lining of the mouth or throat
Russells sign: calluses on knuckles and back of hands due to repeated trauma from incisors
Perimolysis, or severe dental erosion of tooth enamel
Swollen salivary glands (for example, in the neck, under the jaw line)
Gastroparesis, or delayed gastric emptying
Constipation or diarrhea
Tachycardia or palpitations
Hypotension
Peptic ulcers
Infertility
Constant weight fluctuations are common
Elevated blood sugar, cholesterol, and amylase levels may occur
Hypoglycemia may occur after vomitingThese are some of the many signs that may indicate whether someone has bulimia nervosa:
A fixation on the number of calories consumed
A fixation on and extreme consciousness of ones weight
Low self-esteem and/or self-harming
Suicidal tendencies
An irregular menstrual cycle in women
Regular trips to the bathroom, especially soon after eating
Depression, anxiety disorders and sleep disorders
Frequent occurrences involving consumption of abnormally large portions of food
The use of laxatives, diuretics, and diet pills
Compulsive or excessive exercise
Unhealthy/dry skin, hair, nails, and lips
Fatigue, or exhaustionAs with many psychiatric illnesses, delusions can occur, in conjunction with other signs and symptoms, leaving the person with a false belief that is not ordinarily accepted by others.People with bulimia nervosa may also exercise to a point that excludes other activities.