Human acid protease

Several aryl esters of 6-chloromethyl-2-oxo-2//-l -benzopyran-3-carboxylic acid act as human Lon protease inhibitors (alternate substrate inhibitors)46 without having any effect on the 20S proteasome. Proteasomes are the major agents of protein turnover and the breakdown of oxidized proteins in the cytosol and nucleus of eukaryotic cells,47 whereas Lon protease seems to play a major role in the elimination of oxidatively modified proteins in the mitochondrial matrix. The coumarin derivatives are potentially useful tools for investigating the various biological roles of Lon protease without interfering with the proteasome inhibition. 

Another approach to a-ketoamide peptide mimetics was employed by Xu et al. [33] for the preparation of a human cytomegalovirus protease inhibitor library. In this case the oxidizable -OH group, protected as formate, belonged to the starting isocyanides. Thus, the reaction between N-acylated a-amino acids, amines, aldehydes, and isocyanides 42 afforded the a-hydroxyamides 43 in modest yields. Cleavage of the O-formyl bond was accomplished during the reaction by employing two... 

ProtScale tool of ExPASy computes amino acid scale (physicochemical properties/parameters) and presents the result in a profile plot. Perform ProtScale computations to compare the hydrophobicity/polarity profiles with %buried resi-dues/%accessible residues profiles for human serine protease with the following amino acid sequence. 

Pallares I et al (2008) Direct interaction between a human digestive protease and the mucoadhesive poly(acrylic acid). Acta Cryst Sect D 64 784-791 PDBID 2V77... 

The amino acid compositions vary widely and do not indicate any relationship among the enzymes. However, there is one unusual feature. In four proteins the basic amino acid content is exceptionally low. Human gastricsin and human pepsin have no lysine and contain only one histidine and three arginine residues per molecule. Porcine pepsin has one lysine, one histidine, and two arginine residues. Penicillopepsin has five lysines, three histidines, and no arginine. The significance of this unusual feature, which is not shared by other acid proteases, is not clear. 

R. C. Thompson and K. Ohlsson. Isolation, properties and complete amino acid sequence of human leukocyte protease inhibitor, a potent inhibitor of leukocyte elastase. Proc. Natl. Acad. Sci. USA 83 6692 (1986). 

The human immunodeficiency virus protease (HIV-PR), an aspartic acid protease, is involved in the processing of viral polyproteins and is therefore essential for the production of new infectious virions. This enzyme is one of the best-characterized macromolecules from the vantage of drug design, with several hundred crystal structures determined to date. Protein crystallography has contributed in many... 

Lim GP, Calon F, Morihara T, Yang F, Teter B, Ubeda O, Salem N Jr, Frautschy SA, Cole GM (2005) A diet enriched with the omega-3 fatty add docosahexaenoic acid reduces amyloid burden in an aged Alzheimer mouse model. J Neurosd 25 3032-3040 Lin X, Koelsch G, Wu S, Downs D, Dashti A, Tang J (2000) Human aspartic protease memapsin 2 cleaves the )-secretase site of P-amyloid precursor protein. Proc Natl Acad Sci USA 97 1456-1460... 

To study its mode of inhibition, we prepared several derivatives and measured their kinetics of inhibition. Both N-acetyl-statine and N-acetyl-alanyl-statine are competitive inhibitors for pepsin with values of 1.2 X lO M and 5.65 x 10 M, respectively. The value for N-acetyl-valyl-statine is 4.8 x 10 M. These statyl derivatives, therefore, are very strong inhibitors. The value for N-acetyl-statine is 600-fold smaller than that of its structural analog N-acetyl-leucine. The derivative which contains two statyl residues in a tetrapeptide exhibits inhibitory properties which approach those of pepstatin itself. Other acid proteases, human pepsin, human gastricsin, renin, cathepsin D, the acid protease from R. chinensis and bovine chymosin, also are inhibited by pepstatin and its derivatives. We suggest that the statyl residue is responsible for the unusual inhibitory capability of pepstatin and that statine is an analog of the previously proposed transition state for catalysis by pepsin and other acid proteases. 

ACID PROTEASE AND ITS PROENZYME FROM HUMAN SEMINAL PLASMA... 

An acid protease with an optimum pH of 2.5 was first described in human seminal plasma as pepsin and pepsinogen (1), but had not been purified or characterized. Recently, we have purified the acid protease and its proenzyme from human seminal plasma (2,3). In many respects, the properties of seminal plasma acid protease are similar to those of gastric pepsin. Since the proenzyme is more stable than the active enzyme in alkaline solution and can be converted into its active form in acidic solution, the acid protease is likely to exist in seminal plasma, at the physiological pH around 7.5 (4), in proenzyme form. 

Conversion of the proenzyme into its active form. We concluded that only the proenzyme form of acid protease can exist in human seminal plasma at the physiological pH of around 7.5 therefore, we investigated activation of proenzyme in acid medium. The purified proenzyme was incubated in 1 mM HCl, pH 3, for 1 hr, and then chromatographed on Sephadex G-50 column. The proenzyme was converted into an active form and some peptide of small molecular weight was released (Fig.2). As shown in Table II, when the amino acid analyses of the proenzyme, the active form, and activation peptide were carried out, the number of each amino acid residue of the proenzyme agreed well with the additive value between the number of that amino acid in the active form and activation peptide. This supported the conversion of the proenzyme to an active form. The amino acid composition of the active protease and of the proenzyme were comparable to those of bovine pepsin (10) and pepsinogen (11). However, definite differences are present. About forty residues which carried most of the basic amino acids, were released from pepsin, while sixty-nine residues, which carried about 30% of basic amino acid of the precursor were liberated from the proenzyme of seminal plasma acid protease. 

Acid protease activity in human seminal plasma... 

Amino acid composition of the proenzyme, the acid protease, and the activated peptide of human seminal plasma. 

Clearly, the proenzyme is the only form of acid protease that exists in human seminal plasma at its physiological pH of 7,2-7.8. If, on the other hand, the proenzyme form could be converted into its active form in seminal plasma, the latter would have then been destroyed at the slightly alkaline pH of seminal plasma. Thus, the protease activity would not have remained constant, but would have decreased as the time of incubation increased. Since this was not observed, the activation must not be taking place in the seminal plasma. 

Enzymes Degrading Macromolecules. Enzymes that degrade macromolecules such as membrane polysaccharides, stmctural and functional proteins, or nucleic acids, have all shown oncolytic activity. Treatment strategies include the treatment of inoperable tumors with pepsin (1) antitumor activity of carboxypeptidase (44) cytotoxicity of ribonudease (45—47) oncolytic activity of neuraminidase (48—52) therapy with neuraminidase of patients with acute myeloid leukemia (53) antitumor activity of proteases (54) and hyaluronidase treatment in the management of human soHd tumors (55). 

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