Human liver amino acid composition

The amino-acid composition reported by Porter, Sweeny and Porter (64) can be considered as a preliminary result. Thus, the values given by Hartz and Deutsch (67) for human erythrocuprein and by Carrico and Deutsch (8) for the corresponding proteins from human liver and brain should be closest to the actual amino-acid composition. It is still uncertain how many tryptophan residues are present in human erythrocuprein. From measurements of the decrease of the fluorescence emission in the presence of N-bromsuccinimide it was concluded that 1.25 moles of tryptophan per mole of protein are present (92). With MCD studies (78) and chemical analysis by the method of Spies and Chambers (93) the absence of tryptophan residues was demonstrated using bovine erythrocuprein. Other spectrophotometric methods developed by Edelhoch (94) or Beaven and Holiday (95) detected 0.4—0.9 mole of tryptophan per mole of the bovine protein (72). 

The amino acid composition of human arylsulfohydrolase B is known (McGovern et al., 1982). The enzyme contains a low amount of methionine and cysteine. The amino acid compositions of human and cat liver arylsulfo-hydrolases B differ remarkably from those from ox brain (Bleszynski and Roy, 1975) and liver (Farooqui and Roy, 1976). The latter two contain rather large amounts of proline, leucine, glycine, and tyrosine. Relative to arylsulfohydrolase A, the arylsulfohydrolases B from ox brain and liver contain a higher proportion of basic amino acids, accounting for their higher... 

Glutathione peroxidase has a molecular weight between 76,000 and 92,000 daltons and contains four identical 19-23,(X)0 dalton subunits , each of which contains a single selenocysteine residue . Purified forms of the enzyme have been obtained from the red blood cells of cattle , sheep and humans as well as from rat liver and bovine lens . An amino acid composition of homogeneous rat liver glutathione peroxidase has been determined and an X-ray diffi-action study at 2.8 A resolution has been published . There is some discrepancy between these two studies since the amino acid analysis indicates two cysteine residues per subunit which were not detected by the X-ray study. This point will have to be clarified. The X-ray study has shown that the active selenocysteines are found in flat depressions on the surface of the molecule which exists in long a-helices. 

All the lysosomal thiol proteinases described in Section II have been isolated only recently and few structural studies have been carried out. The amino acid composition of only cathepsin B has been reported and is quite similar to those of cathepsin B from human liver (75) and rat liver (19) however Ouchterlony double difPiision analysis with antiserum against rat liver cathepsin B showed no immunological cross reactivity (40). All the lysosomal enzymes examined were shown to contain carbohydrate. The 111 of Asn is a glycosylation site in rat liver cathepsin B (128) but no detailed analysis of this carbohydrate has been reported. Since human liver cathepsin H can be purified on Con A-Sepharose (12), it may also contain a carbohydrate moiety. Rat liver cathepsin H and L also bind to Con A-Sepharose. 

The amino acid composition of rabbit liver cathepsin B was similar to those reported previously for the enzymes from rat (23,24), mouse (25), and human (26) liver (Table III). The amino acid compositions of rabbit liver cathepsins M and B were similar except for higher contents of serine, histidine, cysteine, and tryptophan in the former. The molecular weights, based on the results of SDS gel electrophoresis, are also similar for cathepsin M and cathepsin B. The enzymes from rabbit liver are both glycoproteins, containing 2-3 equivalents each of mannose and glucosamine, the latter presumably present as N-acetylglucosamine (unpublished observations). 

Draper, R. K., Fiskum, G. M., and Edmond, J., Purification, molecular weight, amino acid and subunit composition of arylsulfatase A from human liver. Arch. Biochem. Biophys. 171, 525-538 (1976). 

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