Paul Melius

Thermal condensation of a mixture of six amino acids

Abstract Amino acids can be converted to peptides by the process of heating if the mixture is dry and if the appropriate proportion of glutamic acid as the dominant monomer is present. Three thermal peptide fractions of the diffusible fraction were isolated in this study. Trifluoracetic acid (TFA) hydrolysis was utilized to open the blocked N-terminal group before performing the dansylation reaction. When the molecular weight of the thermal peptide increased, the proportion of neutral amino acids increased slightly, with a decrease in the concentration of glutamic acid. Quantitative analysis of amino acid composition is also reported.

Characterization of Benzo[a]Pyrene metabolites formed by 3-methylcholanthrene-induced goldfish, black bullhead and brown bullhead

Metabolites of BaP formed by 3-MC-induced goldfish (Carassius auratus), black bullhead (Ictalurus melas), brown bullhead (Ictalurus nebulus) and rat have been separated by HPLC. The main metabolites in both bullhead species and the rat were 3-hydroxy-BaP and BaP 9,10- and 7,8-dihydrodiols, whereas BaP 1,6- and 3,6-diones and 9- and 3-hydroxy-BaP predominated in the goldfish. Induced rat formed over 10 times as many total metabolites as the fish. No induction was observed in the 3-MC-treated brown bullheads kept at 7 degrees C. TCPO and alpha-naphthoflavone decreased metabolite production by 50 and 30%, respectively.

Enhanced inhibition of both cellular protein synthesis and malate dehydrogenase by aged aquoplatinum(II) complexes.

Previous studies have shown cis-diamminedichloroplatinum(II) (Cis) an effective anti-tumour agent in man and animals. Evidence is presented here that formation of aquo complexes of this platinum derivative will significantly enhance its inhibitory properties with respect to two separate biochemical functions, namely inhibition of protein synthesis in hamster medulloblastoma cells and in inhibiting the activity of L-malate dehydrogenase (MDH) in a cell free system. Inhibition of cell protein synthesis rises from 8% using freshly dissolved drug to 30% when aged solutions of drug are employed at an inhibitor concentration of 0.1 mM. The inhibitory enhancement seen using purified malic dehydrogenase increases from 16% (fresh) to 57% (aged) at an inhibitor concentration of 1 mM.

Inhibition of leucine aminopeptidase and malate dehydrogenase by aquoplatinum (II) complexes

Abstract Halide complexes of platinum have been previously shown to inhibit tumors and cell growth as well as to possess immunosuppresive activity. Evidence is presented here that the active species in Rb2PtBr4 solutions which inhibits both leucine aminopeptidase ( l -leucyl-peptide hydrolase, EC 3.4.1.1) and malate dehydrogenase ( l -malate:NAD+ oxidoreductase, EC 1.1.1.37) enzymes is PtBr3(H2O)−. The aquo complex earlier has been shown to be in equilibrium with PtBr42− in solution and the rate of formation is known. This is in accord with the rate of inhibition of enzyme activity by fresh solutions of Rb2PtBr4. This reagent should provide another method for studying the active site and function of enzymes.

Characterization of the subunits of swine kidney leucine aminopeptidase

Abstract The swine kidney leucine aminopeptidase obtained in this study was found to have a molecular weight of 255 000 ± 5000, by the Yphantis method. The subunit, obtained in 6 M guanidine, 0.5% β-mercaptoethanol, has a molecular weight of 63 500 as determined by the Yphantis method. The enzyme is probably converted to a lower molecular weight species, s 20, w = 6.0 S from the native enzyme s 20, w = 13.1 S when dialyzed against 4 M urea, 0.05 M Tris solution. At the same time the enzyme is inactivated. When dialyzed against 4 M urea, 0.05 M Tris and 0.05 M MgCl 2 , the enzyme is not converted to the 6.0-S species and retains full enzymic activity. Dialysis of the enzyme against 0.5 mM EDTA (pH 8.0) completely inactivated it and converted it to a s 20, w = 5.5-S protein. It had been demonstrated earlier that 0.05 M barbital and 0.5 mM MgCl 2 protected the enzyme against inactivation by 5 mM EDTA. These results indicate a potential role for Mg 2+ in subunit structure of the leucine aminopeptidase similar to the role suggested by Simpson and Vallee 12 for zinc in alkaline phosphatase.

Interactions of cis- and trans-platinum(II) complexes with dehydrogenase enzymes in the presence of different mono- and polynucleotides: evidence for a ternary complex.

The inhibition of several dehydrogenase enzymes by cis- and trans-Pt(NH3)2Cl2 have been measured in the presence of baker yeast ribonucleic acid (RNA), calf thymus and salmon sperm deoxyribonuclic acid (DNA) and several mononucleotides (AMP and ATP). The binding constants for the interaction of the platinum complexes to the nucleotides have been calculated and a comparison of those values to the previously calculated platinum complex-enzyme binding constants strongly suggest that platinum compounds are more tightly bound to the enzymes. The binding of the platinum complexes to most of the enzymes was decreased in the presence of any nucleotide, yet it was observed that when using rabbit muscle (M4) lactate dehydrogenase the mononucleotides reduced the binding to a lesser degree while the polynucleotides actually enhanced the platinum-enzyme interaction. The implications of these interactions are discussed.

Effects of divalent cations and sodium taurocholate on pancreatic lipase activity with gum arabic-emulsified tributyrylglycerol substrates

The effects of Ca2+ and/or sodium taurocholate on lipase activity with gum arabic-emulsified tributyrylglycerol substrates were investigated. Calcium was found to slightly increase lipase activity while bile salts showed marked inhibition except at very low concentrations. Calcium eliminated inhibition seen with low concentrations of bile salts and reduced the inhibition seen at higher bile shift of the enzyme from the alkaline region in the absence of bile salt to the slightly acidic region in the presence of bile salt. Calcium was shown to eliminate the time lag periods between enzyme addition and maximum rate of hydrolysis seen at low substrate concentrations and the time lag noted when bile salts were included with normal (substrate concentration not limiting) assay concentrations of substrate. Zeta potential measurements indicated that Ca2+ reduced the negative charge on the gum arabic-emulsified particle while bile salts did not increase the negative charge. Commercial preparations of gum arabic were found to have significant concentrations of Ca2+ and Mg2+.

Structure of thermal polymers of amino acids

When glutamic acid is a predominant amino acid in a thermally polymerized mixture of amino acids, pyro Glu is exclusively found at the N-terminal end of the poly-amino acid polymer. It probably initiates the polymerization process. Lysine-containing polymers will probably contain epsilon N-(glutamyl)L-lysine cross links which may account for the higher molecular weights observed in these polymers (100-200 000). Incorporation of some amino acids facilitates the incorporation of others. When utilizing mixtures of three to eight amino acids with glutamic acid as one of the amino acids, some fractions are obtained which include all the amino acids in the polymerization mixture. The biosynthesis of glutathione, gramicidin, tyrocidine and cell-wall polypeptides has demonstrated that non-random amino acid sequence peptides can be biologically synthesized without the direct participation of nucleic acids. That is, the enzymes appear to provide adequate chemical specificity to form non-random amino acid sequence peptides. The properties and replication of the scrapie agent may provide us with more profound insight as to the evolution of purely physical-chemical systems into biological systems.

Lipids associated with pancreatic lipase during purification

Abstract 1. 1. Lipids appear to influence the outcome of the purification of porcine pancreatic lipase, affecting the solubility as well as the stability of the enzyme at different purification steps. The relative distribution of these lipids determined the density of the lipid-enzyme complex. 2. 2. Evidence presented suggests that pancreatic lipase is not a lipoprotein in vivo but becomes one on homogenization of the pancreatic tissue. The most active enzyme is free of lipid and is soluble in water. 3. 3. The apparent instability of pancreatic lipase during purification appears to be due to interaction between the enzyme protein and solvents, like n-butanol or acetone, which act as irreversible denaturants. The lipid material protects the enzyme from denaturation and, in addition, enhances the collection of the enzyme-lipid complex at the n-butanol-water interphase.

Interactions of platinum complexes, peptides, methionine and dehydrogenases

Eight platinum-methionine complexes have been investigated as inhibitors of the alcohol (EC 1.1.1.1) and lactate (EC 1.1.1.27) dehydrogenase systems. While only one complex, Pt(Met)Cl2, had two halogen ligands on the platinum, all the complexes were able to inhibit both enzyme systems. Of the various methionine and histidine containing peptides evaluated, the dipeptide Met-Met gave the best protection against inhibition by N-alkyl-substituted ethylenediamine-platinum complexes. The histidine containing peptides gave a slight protection against the inhibition by beta-[Pt(Met)(NH3)Cl]Cl. Thus it appears that in the enzyme systems studied, the methionine acts as a strong ligand for platinum.