Seminal plasma, acid protease

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. 

Hydrolysis of cervical mucus protein by the acid protease. The pattern of cervical mucus protein before and after hydrolyzing by acid protease were shown in Figure 4. The major protein band was lost in cervical mucus treated with acid protease. The appearance of new bands of smaller molecular weight indicated that hydrolysis had occurred. However, this protein band was also lost in cervical mucus hydrolyzed with chymotrypsin at pH 7.8, suggesting a rather nonspecific hydrolysis. The cervical mucus protein seemed to be hydrolyzed to a greater extent by the seminal plasma acid protease than by chymotrypsin. 

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

It has been suggested that the proteolytic activity of seminal plasma is an essential prerequisite to sperm penetration through the cervical mucus (6) thus, the possible physiological function of the acid protease is also discussed in this report. 

Acid protease activity in seminal plasma at pH 3.0 and 7,5. Previous results (3) have shown that the acid protease, pH optimum of... 

Acid protease activity in human seminal plasma... 

The activity of acid protease in seminal plasma was determined at 37 for 30 min using hemoglobin as substrate. 2 ml of reaction mixture contains 15 mg Hb, 20 X seminal plasma (corresponding to 0.6 - 0.7 enzyme unit) and 0.1 M citric acid-phosphate buffer, pH 2.5. 

Treatment of Seminal Plasma Prior to Assay Acid Protease Activity (AA2gQ/30 min)... 

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. 

Digestion of bovine serum albumin, ovalbumin and dimethylcasein at various pH by acid protease from seminal plasma... 

An acid protease, with an optimum pH of 2.5, exists in seminal plasma in a proenzyme form. In acidic pH, the proenzyme is converted into the active form, resulting in the release of small molecular... 

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