Forms of sulfur compounds

Sulfur is excreted in urine in three forms:

1. Inorganic SO4 – 80 to 85%

2. Organic esters or “ethereal sulfates” – 5%

3. Neutral sulfur – (organic sulfate) – 15 to 20%.

Source: Most of urinary sulfur arises from metabolism of proteins, specially from sulfur-containing aminoacids cysteine, cystine and Methionine.

Note:Methionine indirectly contributes through cysteine. A small amount obtained from S-containing vitamins like thiamine, Biotin, Lipoic acid. Food proteins contain on an average 1% of sulfur. Excretion of S in urine varies with:

(i) protein intake in diet and

(ii) rate of tissue protein break down.

Normal value and clinical significance: total urinary sulfur varies from 0.8 to 1.4gm per 24hrs (average =1.0gm). urinary N:S ratio = 13 to 16 on a high meat diet and during fasting.

Ethereal sulfur

Range from 0.06 to 0.12 gm/day. It consists ofNa and K salts of sulfuric acid esters of phenols such as indoxyl, skatoxyl, phenol and cresol. These ethereal SO4 represent detoxication compounds of phenols and are formed in liver. Some of the phenolic substances originate through:

(i) Bacterial action in the gut,

(ii) Some appears to be formed in tissue metabolism.

Indoxyl and skatoxyl are formed practically entirely by putrefactive decomposition of tryptophan in the gut and phenol and cresol from tyrosine. Both substances are esterified with H2SO4 in liver and excreted in urine as the Na and K salts. K-salt of indoxyl sulphuric acid is called as Indican and is excreted in urine.

Clinical importance: Excretion of Indican in urine is taken as a rough index of intestinal putrefaction.

1.Clinically in intestinal obstruction due to putrefaction, and absorption of these products in carcinoma liver, cholera, thyphus, excretion of ethereal SO4 increases. In cholera and thypus, sufficient indican is excreted to cause urine to assume a bluish tinge on standing.

2. Bacterial decomposition of tryptophan in pus anywhere in the body in pathological conditions increase the excretion of indican.

Neutral Sulfur Fraction

Ranges from 0.08-0.16 gm/day. It is composed of heterogenous mixture of sulfur compounds. These include cystine, methionine, urochrome, thiosulfates, oxy-proteic acids, thiocyanates, bile acids and taurine and its derivatives.

Clinical significance: Increase – Urinary sulfur (neutral fraction) is increased in: