Cystine is a molecule formed by 2 cysteines (Cys) joined by a disulfide bond (Cys-Cys). Levels of cystine are expressed in terms of half-cystine (approximates cysteine). Initial methods for measuring cystine reduced cystine followed by measurement of cysteine.


Molecular weight of cysteine = 121.16

Molecular weight of cystine = 240.30 = (2 * cysteine) - (2 * hydrogen)


Conversion units:

(1) from mg/dL of half-cystine to µmol/L of half-cystine: multiply by 83.3

(2) from µmol/L half-cystine to mg/dL half-cystine: muliply by 0.012

(3) µmol/L of half-cystine to µmol/L cystine: divide by 2


concentration of half-cystine per mg protein =

= (half-cystine in µmol/L) / (protein in mg/L)


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