Methionine microbiological assay

Provisional values for the amino acid composition of crystalline botulinus toxin have been determined by Buehler et al. (19), using microbiological assay methods. The following amino acids were shown to be present aspartic acid, valine (4.0%), serine (3.0%), threonine (7.3%), arginine (3.2%), lysine (7.9%), histidine (1.0%), glutamic acid (14.9%), leucine (8.9%), isoleucine (11.0%), cysteine (0.48%), methionine (0.83%), phenylalanine (1.08%), and tyrosine (9.5%). The total is 73%. 

Major vitamin Bi2-dependent metabolic processes include the formation of methionine from homocysteine, and the formation of succinyl coenzyme A from methylmalonyl coenzyme A. Thus, apart from directly determining vitamin B12 concentration in serum, elevated levels of both methylmalonic acid and homocysteine may indicate a vitamin B12 deficiency. Serum cobalamine concentration is often determined by automated immunoassays using an intrinsic factor as binding agent. These assays have mainly replaced the microbiological methods. Literature data about vitamin B12 concentration in serum varies. Values <110-150pmoll are considered to reflect deficiency, whereas values >150-200pmoll represents an adequate status. 

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