Ss

0(0)

70 (21)

20(1)

Bonded

4(2)

0(0)

0(0)

13(6)

17(5)

20(1)

Free + SS

2(1)

0(0)

0(0)

Bonded + SS

2(1)

3(1)

20(1)

Free + bonded

0(0)

0(0)

0(0)

" The distribution among different cellular locations (extracellular, intracellular, and periplasmic) of different oxidation states of cysteines in 81 analyzed proteins. Free, Cysteines, free thiols; SS, cystines, that is, cysteines in disulfide bridges; bonded, cysteines liganded to a prosthetic group or in an active center; —, proteins without any cysteine; and combinations of the subgroups (free + SS; bonded + SS;free + bonded).

already show the most variation in the redox state of cysteine. There is a high (but not perfect) correlation between the oxidation state of cysteine and the location of the protein within the cell; intracellular proteins all have reduced cysteines, whereas one-tenth of extracellular proteins also have reduced cysteines.

Occurrence in Secondary Structures, Linked Structures

The frequencies of oxidized and reduced cysteines in secondary structure elements are similar. Cysteines occur most often in coil structures, and these cysteines are also the most conserved, but conserved bonded cysteines also occur in helixes (Table II). The high frequency of half-cystines in coil structures is not connected with a distortion of the regular structure by disulfide links. Such a situation occurs table n

Cysteine Conservation and Occurrence in Secondary Structures"

Secondary structure

All residues frequency (%)

Nonbonded cysteine

Bonded cysteine

Frequency (%

0 Conservation

Frequency (%) Conservation

Helix

0 0

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