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H D Belitz

Publications and source records attributed to H D Belitz.

17 recordsLinked to original sources
PubMed1979

Multiple forms of soluble monophenol, dihydroxyphenylalanine: oxygen oxidoreductase (EC 1.14.18.1) from potato tubers (Solanum tuberosum). IV. Association and dissociation phenomena.

The soluble phenol oxidase of various potato juices (adjusted from physiological pH to pH 4.5, 7.0 and 7.8) was separated by gel chromatography into multiple molecular forms. In acid or neutral and alkaline potato juices, low-mol.-wt. (less than 150,000 daltons) or high-mol.-wt. (greater than 150,000 daltons) enzyme forms predominate, respectively. Conversion of the low-mol.-wt. enzyme forms into high-mol.-wt. enzyme forms, and vice versa, was achieved by changing the pH values from acidic to neutral or alkaline pH, and vice versa. This substantiated our previous idea that the enzyme multiplicity arises from association of various subunits. In alkaline potato juice, considerable loss of monophenol oxidase activity (assayed at pH 6.0) occurred. This confirmed our previous findings that o-diphenol oxidase is more alkali-stable than monophenol oxidase.

Catechol Oxidase↗
PubMed1979

Multiple forms of soluble monophenol, dihydroxyphenylalanine: oxygen oxidoreductase (EC 1.14.18.1) from potato tubers (Solanum tuberosum). III. Influence of pH on the molecular weight distribution of enzyme activity in potato juice.

Gel chromatography on Sepharose and on Sephadex was used to separate the soluble phenol oxidase in various potato juices into multiple molecular forms ranging from 36,000 to 800,000 daltons. Adjustment of potato juice from physiological pH (ca. 6) to pH 4.5 or to pH 7.8 resulted in the predominance of low-mol.-wt. (less than 150,000 daltons) or high-mol.-wt. (greater than 150,000 daltons) enzyme forms, respectively. This suggests association phenomena of subunits. In potato juice of physiological pH and in potato juice adjusted to pH 4.5, all enzyme forms exhibited both monophenol and o-diphenol oxidase activities (assayed at pH 6.0). In potato juice adjusted to pH 7.8 considerable loss of monophenol oxidase activity (assayed at pH 6.0) occurred. This suggests that o-diphenol oxidase is more alkali-stable than monophenol oxidase. The significance of these findings for enzyme purifications and for the in vivo action of the enzyme is discussed.

Catechol Oxidase↗
PubMed1978

Studies on enzymic browning of potatoes (Solanum tuberosum). IV. Relationship between tyrosine turnover and rate of browning.

Using analytical data from the literature the tyrosine turnover was calculated by a method published previously by us for 72 potato samples with different rates of browning. The samples included 9 varieties grown at three locations in 1969, which were analysed after harvest and after different times of storage at three temperatures. For 58 samples (81%) this calculation led to the same classification of the varieties as did visual observation of the rate of discolouration. It is concluded that enzymic browning of potatoes is correlated rather with tyrosine turnover, which depends on the concentrations of phenol oxidase, tyrosine, chlorogenic acid, and ascorbic acid, than with any single parameter.

Ascorbic Acid↗
PubMed1977

[Relationships between structure and sweet taste of amino acids (author's transl)].

90 amino acids, derivatives of amino acids and other related compounds were tested for their taste quality. The taste thresholds of 35 sweet compounds were determined. From these data some relationships between structure and taste are derived. Essential for sweet taste are the ammonium and carboxylate groups as a bipolar (nucleophile/electrophile) contact unit. The intensity of taste depends on length, shape and polarity of the side chain. Definite conditions in respect to the relative position of the groups to each other must be fulfilled. It is shown by superposition of the steric formulas of selected amino acids, that the binding site of the receptor probably is a hydrophobic tube with a bipolar contact point at one end.

Amino Acids↗
PubMed1977

Multiple forms of soluble monophenol, dihydroxyphenylalamine: oxygen-oxidoreductase (EC 1.14.18.1) from potato tubers (Solanum tuberosum). II. Partial characterization of the enzyme forms with different molecular weights.

Gel chromatography on Sephadex G-200 was used to separate a soluble phenoloxidase from potatoes (var. Maritta) into at least six active fractions with dopa (dihydroxyphenylalanine) as substrate. Only high-molecular-weight-enzyme forms exhibited monophenoloxidase activity. Re-chromatography of the highest-molecular-weight form gave the same molecular weight distribution as with the crude enzyme. The molecular weights indicate association phenomena of subunits with a molecular weight of about 36000 daltons. According to polyacrylamide-gel electrophoresis, several monomeric forms with differnt isoelectric points seem to be present. This suggests that the large number of multiple forms of the enzyme arises from various combinations of identical and/or different subunits. SDS polyacrylamide gel electrophoresis failed to show the monomeric forms; the dimer and higher oligomers were obtained.

Catechol Oxidase↗
PubMed1977

[Studies on enzymic browning of potatoes (Solanum tuberosum). II. The quantitative relationship between browning and its causative factors (author's transl)].

Ten potato varieties, with different rates of browning, were analyzed quantitatively for phenoloxidase, tyrosine, chlorogenic acid, caffeic acid, and for reducing substances (ascorbic acid). The rate of tyrosine turnover was calculated from the data. The fact that the further reactions of the primary oxidation products leading to browning only take place after complete oxidation of the reducing substances, was taken into account. This leads to the same classification of the varieties as does visual observation of the rate of discolouration. Thus a clear relationship between browning and potato constituents is demonstrated.

Ascorbic Acid↗
PubMed1977

Studies on enzymic browning of potatoes (Solanum tuberosum). III. Kinetics of potato phenoloxidase (EC 1.14.18.1 monophenol, dihydroxyphenylalanine: oxygen-oxidoreductase).

From initial velocity studies a sequential mechanism for the reactions catalysed by phenoloxidase from potatoes is indicated. The data are in accordance with an ordered addition of oxygen and phenolic substrate to the enzyme, with oxygen being the first substrate bound at thermodynamic equilibrium. The Michaelis constants for L-tyrosine, L-dopa, and chlorogenic acid are 1.4 X 10(-3), 3.3 X 10(-4), and 1.4 X 10(-4) mol/l, respectively. The dissociation constant for the enzyme-oxygen complex is about 10(-3) mol/l. In the presence of chlorogenic acid no lag phase occurs in the course of L-tyrosine oxidation. With increasing amounts of chlorogenic acid the tyrosinase activity goes through a maximum. The significance of these findings for the in vivo action of the enzyme is discussed.

Catalysis↗
PubMed1977

[Studies on enzymic browning of potatoes (Solanum tuberosum). I. Phenoloxidases and phenolic compounds from different varieties (author's transl)].

31 samples of potato varieties with slow, medium and fast rates of browning were studies. Characteristic enzyme patterns were obtained from polyacrylamide gel electrophoresic of the phenoloxidases of varieties with different discolouration rates. The differences lie mainly in the intensities of the enzyme bands. The qualitative determinaiton of the phenols showed no significant differences. Tyrosine, chlorogenic acid and caffeic acid produce coloured oxidation products; the characteristic colour gradations of in vivo browning were only observed in the presence of tyrosine. It is concluded that the same reactions take place during the discolouration of all the varieties.

Catechol Oxidase↗
PubMed1977

[Inhibitors for trypsin and chymotrypsin in seeds of the broad bean (Vicia faba) (author's transl)].

Several inhibitors for trypsin and chymotrypsin were detected in seeds of Vicia faba by isoelectric focussing. Their isoelectric points are at pH 8.5 (main peak with shoulder), at pH 9.1 (minor peak with shoulder) and in the range of pH 9.1-6.4 (several minor peaks with significant lower activities). From the mixture of inhibitors obtained by affinity chromatography on carrier bound trypsin, three inhibitors were isolated by preparative electrophoresis in polyacrylamide gel. On electrophoresis these inhibitors behaved uniformly at pH 9.2 and at pH 4.0. Their molecular weights are about 6000 daltons. The amount of basic amino acids is high, while methionine and isoleucine are absent. Beside of trypsin and chymotrypsin some serine proteinases of microbiol origin are inhibited. The thermal stability is quite high. The Vicia inhibitors therefore differ significantly from the Phaseolus inhibitors in several properties.

Chymotrypsin↗
PubMed1976

[Comparative studies on the reactive sites against trypsin of some inhibitors from phaseolus coccineus and phaseolus vulgaris (author's transl)].

Three of the trypsin chymotrypsin inhibitors from the seeds of runner beans (Phaseolus coccineus L.), PCI 3,4(2), and 5, and three of the inhibitors from the seeds of french beans (Phaseolus vulgaris var. nanus), PVI 3, 4, and 5, contain a lysine residue in the reactive site against trypsin. One of the inhibitors from Phaseolus coccineus, PCI 2, contains an arginine residue there. All seven Phaseolus inhibitors investigated are double headed.

Lysine↗
PubMed1976

[Inhibition of cathepsins from trout muscle and from bovine spleen by proteinase inhibitors of potato tubers (author's transl)].

The cathepsins D from trout muscle and from bovine spleen, as well as cathepsin A from bovine spleen are inhibited by a crude proteinase inhibitor from potato tubers. Cathepsins C and B1 are not inhibited. It was shown by isoelectric focussing that several inhibitors for cathepsin D are present in potatoes. Those with isoelectric points at pH 9.2, 9.1, 9.0, 8.9, 8.5 inhibit cathepsins D both from trout muscle and from bovine spleen. In addition some inhibitors with isoelectric points at pH 6.6, 6.5, and 6.2 were observed, which inhibit cathepsin D from trout muscle only.

Animals↗
PubMed1976

[Relations between structure and bitter taste of amino acids and peptides. II. Peptides and their derivatives (author's transl)].

About 80 peptides and their derivatives were tested for bitter taste. The taste thresholds are in the range of 70-80 muMol/ml (Gly-Val) to 0.01-0.02 muMol/ml (Bacitracin). They are dependent on nature and number of the side chains and on the hydrophobicity of the whole molecule. An estimation of the taste thresholds of all di-and tripeptides with known amino acid composition is possible on the basis of their hydrophobicity. As could be shown recently for bitter amino acids, a polar (electrophilic) and a hydrophobic group are essential requirements for bitter peptides also. This model corresponds to all sensory results, e.g. to the bitter taste of all hydrophobic peptides independent on their sequence and configuration and to the sweet taste of L-aspartyl dipeptide esters.

Amino Acids↗
PubMed1976

[Occurrence of bitter taste after roasting of proteins (author's transl)].

Proteins of animal and plant origin (e.g. casein, zein, soyprotein, gliadin), heated to 260 degrees C for 10 min, yield aqueous extracts of strong bitter taste. The thresholds (0.0005-0.008%) are in the range of the value for chininhydrochloride (0.001%) and are much lower than thresholds for enzymatic protein hydrolyzates. Polysaccharides, heated under identical conditions (e.g. cellulose, starch, agar, carrageene), don't yield bitter products. It is assumed, that proteins are important precursors for bitter compounds on roasting.

Caseins↗
PubMed1975

Multiple forms of soluble monophenol, dihydroxyphenylalanine: oxygen-oxidoreductase (EC 1.14.18.1) from potato tubers (Solanum tuberosum).

Upon polyacrylamide gel electrophoresis, a soluble phenoloxidase from potatoes (var. Maritta) revealed 17 multiple forms with activity towards dopa and almost all other o-diphenols tested, but only 5 of the forms reacted with monophenols. Isoelectric focusing of the crude enzyme resulted in 2 main peaks with activity towards dopa, having isoelectric points at pH ranges 4.0-4.7 and 5.1-5.4: smaller amounts of the enzyme at higher pI values were also detected. When activity peaks were controlled by polyacrylamide gel electrophoresis, all bands previously detected by electrophoresis of the crude enzyme were recovered, but all peaks were electrophoretically heterogeneous. Gel chromatography of the crude enzyme showed different molecular forms. Their molecular weights indicated monomer, dimer, tetramer, octamer and polymer (at least hexadecamer) forms with a monomer molecular weight of about 36000.

Catechol Oxidase↗