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Biomedical subjects

Z Bohak

Publications and source records attributed to Z Bohak.

12 recordsLinked to original sources
PubMed1985

Factors affecting the production of plasminogen activator in cultures of normal fibroblasts.

Plasminogen activator (PA) is a serine protease with a proven medical application as a fibrinolytic drug. PA is a normal constituent of animal tissues and is found in low concentration 1-10 U/ml in the supernatant of various cells in culture. We found that certain strains of untransformed human diploid fibroblasts can be adapted to produce PA at levels of 100 U/ml or more by culture with specific combinations of serum and coated substrates. Once the cells are adapted, they continue to produce the enzyme in a medium devoid of serum in which cell proliferation is minimal. The time course of enzyme production revealed that its formation is controlled by negative feedback and stops when its level in the medium reaches a critical concentration. However on removal of the enzyme by continuously replacing the medium, the cells continue to produce enzyme at a constant rate for a period of several weeks. Possible biotechnological configurations for large scale production of this enzyme are now under study. The PA purified from the spent medium of these cells was identified as tissue type activator similar to the melanoma type PA.

Cells, Cultured↗
PubMed1976

The structure of monellin and its relation to the sweetness of the protein.

The sweet protein monellin [1-3] has been shown to consist of two non-identical subunits of 50 and 42 amino acid residues, which were separated electrophoretically and chromatographically. Automatic sequential Edman degradation gave the complete sequence of the longer subunit, and a partial sequency of the shorter one. It was found that the sweetness of monellin requires the undissociated molecule. The individual subunits were not sweet, neither did they block the sweet sensation of sucrose or monellin. Blocking of the single SH of monellin abolished its sweetness as did reaction of the single methionyl residue with CNBr. Since the cysteinyl and methionyl residues appear to be adjacent, it is suggested that this part of the molecule is essential for its sweetness.

Amino Acid Sequence↗
PubMed1975

Modulation of the enzymic activity of chicken pepsin by the covalent modification of its single -- SH group.

The single cysteinyl residue of chicken pepsin was modified with a wide spectrum of reagents to produce mixed disulfides or alkylated derivatives. All these derivatives showed enhanced catalytic activity towards the synthetic peptide Z-Ala-Ala-Phe-OPrP, where OPrP is the 3-(4-pyridyl)-propyl-1-oxy group. The overall catalytic constant kcat/Km for these derivatives was 4 -- 25-fold larger than that of the native enzyme. The activity of the enzyme towards denatured hemoglobin was slightly decreased (10--45%) by these modifications. When the mixed disulfide derivatives were treated with excess mercaptan, the sulfhydryl group was regenerated and activity reverted to that of the native enzyme. The --SH group of chicken pepsin reacted preferentially with reagents containing an aromatic group. The reaction was found to depend on the ionization of a single group, presumably the --SH itself, with a pKa = 7.5. The rate of reaction of the fully deprotonated species with various disulfides was 100--1000-fold smaller than that of the --SH group of glutathione. It is suggested that the groups attached covalently to the sulfhydryl also interact with other amino acid side chains in the protein thereby affecting the active center of chicken pepsin.

Amino Acids↗