Choline requirements

Comparable data are not available with respect to humans, but for rats choline requirements vary widely from individual to individual and from strain to strain. These findings have been published in a... 

Methionine, USP. An adequate diet should provide the methionine ncccs.sary for normal metabolism in the human.. Viethionine is considered an essential amino acid in humans. It is the precursor in the biosynthesis of -adcnosylnie(hio-niiic, which is an important methylating coenzyme involved In a variety of methylations (e.g.. N-me(hyla(ion of norepinephrine to form epinephrine and O-methylation of catecholamines catalyzed by ca(cchul-CI-mcthyl(iansfcra.ses). Adenosylmcthionine also participates in the methylation of pho.sphatidylcthanolaininc to form phosphatidylcholine, but this pathway is not efficient enough to provide all of the choline required hy higher animals hence, adequate dietary availability of choline is ncces.sary. ... 

Quaternary ammonium compounds can be analyzed under similar chromatographic conditions, but without adding boric acid. This includes choline (2-hydroxyethyl-trime-thylammonium hydroxide), which is commonly found in fauna and flora as a basic constituent of lecithin-type phospholipids. The ion-pair chromatographic separation of choline requires an eluent that, in addition to hexanesulfonic acid as the ion-pair re-... 

Deficiency symptoms, including slow growth and fatty infiltration of the hver, have been produced in chicks and pigs. Choline is also concerned with the prevention of perosis or slipped tendon in chicks. The choline requirement of animals is imusually large for a vitamin, but in spite of this, deficiency symptoms are not common in farm animals because of its wide distribution and its high concentrations in foods, and because it can be readily derived from methionine. 

Little is known of choline requirement in either animals or man since the need is dependent, in part, on other sources of methyl groups in the diet, namely methionine and betaine. Elvehjem has suggested that, in the light of animal studies, the human requirement is probably less than 500 mg. daily. This amount may be furnished by the average diet which contains about 250 to 600 mg. of choline. 

The enzymatic hydrolysis of lecithin to fatty acids, glycerol, phosphoric acid, and choline requires the participation of some four enzymes. The enzymes attacking the various bonds of a lecithin molecule are summarized in Table XIV. The bonds which are cleaved are referred to by number in the lecithin formula shown below the same numbers are used in Table XIV to indicate the respective enzymes involved. The cleavage of the fatty acid-glycerol bond, as represented by diagonal lines 1 and 2, is based on hydrolysis studies of simple esters. Diagonal lines 3 and 4 are only provisional, as presumably either a P—0 or C—O bond to phosphate could be cleaved. 

---