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Biomedical subjects

J R Stark

Publications and source records attributed to J R Stark.

17 recordsLinked to original sources
PubMed2001

Studies on digestive proteases from midgut glands of a shrimp, Penaeus indicus, and a lobster, Nephrops norvegicus: Part 1. Proteolytic activity.

Digestive gland protease pH optima and specific activities determined in Penaeus indicus with casein, azocasein, Azocoll, and Congo red fibrin as substrates were pH 7.7-9.2, 210-371 micromol of tyrosine/mg of homogenate protein/min; pH 7.8, 36; pH 6.0-7.0, 7; and pH 8.9-9.2, 7A delta0.001 U/mg of homogenate protein/min, respectively. Activity in the shrimp was stable during frozen storage but relatively labile and very low (1.043 azocasein units) in the Norwegian lobster, Nephrops norvegicus. The high activity in shrimp is significant in aquaculture and may be a source of proteolytic enzymes for industrial use. The rapid deterioration after landing may be a consequence of the high and stable activity. The low activity in the lobster may present a problem in culture and requires a more critical choice of feed as well as further investigation. 4-(2-Aminoethyl)-benzenesulfonyl fluoride hydrochloride was a very convenient, fast-acting, and effective inhibitor of shrimp trypsin and chymotrypsin but did not completely inhibit general protease activity in shrimp and had a negligible effect on the lobster. A significant component of that activity may be from nonserine proteases (such as the exoproteases carboxypeptidase A and B and the leucine aminopeptidases), whose proportion relative to the serine proteases may be greater in the lobster.

Animal Feed↗
PubMed1989

Biochemical studies in marine species--I. NADP(+)-dependent isocitrate dehydrogenase from turbot liver (Scophthalmus maximus L.).

1. An NADP+-dependent isocitrate dehydrogenase was extracted from turbot liver. The enzyme required divalent cations (Mg2+ or Mn2+) for its activity but was inhibited by high salt concentrations. 2. The enzyme had an optimum activity in the pH range between 7.5 and 9.0. The enzymic activity increased with temperature (in the range of 5 to 68 degrees C) with an Ea of 23.5 kJ/mol and a Q10 of 1.34. 3. The apparent Km values for the substrates were 6.5 microM for NADP+, 56 microM for Mg2+, 87 microM for Mn2+ and 4.2 and 73.5 microM for the complexes Mg-isocitrate and Mn-isocitrate, respectively. The physiological significance of these results is discussed. 4. The enzyme was inhibited by citrate and adenine nucleotides. The degree of inhibition depended on the relation between the concentrations and that of magnesium. A possible regulating mechanism is proposed.

Adenine Nucleotides↗
PubMed1988

The iodine-staining properties and fine structure of some mammalian and invertebrate glycogens.

Glycogens from mammalian and invertebrate sources have been compared by measuring the iodine-staining spectra of the debranched polymers and the debranched beta-amylase limit dextrins. From the results, it is concluded that, whereas the interior chains of each group of glycogen are very similar, the exterior chains of the mammalian glycogens generally contain a small number of longer chains which are not found in the invertebrate glycogens.

Ammonium Sulfate↗
PubMed1985

Metabolism in marine flatfish. II. Protein digestion in Dover sole (Solea solea L.).

The digestive tracts of adult and juvenile Dover sole were examined for protease activities. A pepsin-like protease with an optimal pH value of 1.7 predominated in the stomach region, but the main endoprotease action in the foregut, midgut and hindgut regions was optimal in the range of pH 9.5-10.5 and showed good activity towards elastin orcein. Experiments using synthetic substrates suggested the presence of chymotrypsin- and trypsin-like activities optimal between pH 7 and 8. Collagenase activity was also shown to exist in this pH region. The presence of enzymes corresponding to carboxypeptidases a and b and leucine aminopeptidase was indicated. The possible significance of these results to the farming of Dover sole is discussed.

Animals↗
PubMed1985

Metabolism in marine flatfish--III. Measurement of elastase activity in the digestive tract of Dover sole (Solea solea L.).

A critical assessment of different methods for measuring elastase activity in crude preparations has been made using whole intestinal homogenates of Dover sole. The use of the natural substrate elastin or its dyed derivatives gave optimal pH values in the alkaline region (pH 9.4-9.8) whereas artificial substrates showed optimal hydrolysis nearer neutrality in the region pH 8.1-8.2. Exoproteases may interfere with certain assay procedures. The properties of Dover sole elastase have been further investigated using chromatographic techniques which indicated that the main elastase activity has a molecular weight of approximately 19,500 and an isoelectric point in the region of pH 5.7.

Aging↗
PubMed1979

Partial purification and properties of a bacterial isoamylase.

Isoamylase has been prepared by affinity chromatography of a commercial enzyme-preparation from a strain of Cytophaga (also known as a Flavobacterium or Polyangium). The enzyme was not very stable, but the stability could be improved by calcium ions. The enzyme had a very low but significant activity on pullulan and on alpha-dextrins having maltosyl side-chains. This observation, which is contrary to previous reports, has been related to the specificity of isoamylase and other bacterial debranching-enzymes.

Animals↗
PubMed1976

Some properties of a fungal beta-D-glucanase preparation.

A commercial enzyme preparation, of fungal origin, contained a mixture of beta-D-glucanases which were fractionated by ion-exchange chromatography to give a mixture of an endo-(1 leads to 4)- and an exo-(1 leads to 3)-beta-D-glucanase. These two enzymes were then separated by molecular-sieve chromatography on Sephadex G-150. The purified exo-(1 leads to 3)-beta-D-glucanase has a relatively high specificity for (1 leads to 3)-beta-D-glucosidic linkages, and has no action on lichenin.

Fungi↗
PubMed1971

Studies on the structure and metabolism of glycogen in some abnormal human infants.

1. The liver and muscle tissues of 14 human anencephalic babies were examined for glycogen content and structure, and for the activities of several glycogen-metabolizing enzymes. 2. In both tissues glycogen content increased with gestation age; the muscle glycogens had a slightly but significantly lower degree of branching than the corresponding liver glycogens. 3. All the expected glycogen-metabolizing enzymes were present; acid maltase activities were higher and phosphoglucomutase activities were lower than the results reported for human adult tissues. Glucose 6-phosphatase activity increased significantly with gestation age.

Anencephaly↗
PubMed1966

Studies on the metabolism of the protozoa. The molecular structure of the reserve polysaccharide from Astasia ocellata.

1. The flagellate Astasia ocellata synthesizes as reserve carbohydrate a water-insoluble polysaccharide (paramylon) containing chains of beta-(1-->3)-linked d-glucose residues. 2. The average chain length, determined by methylation analysis, is about 43, and the minimum degree of polymerization from periodate oxidation data is 50-55. Most of the molecules are therefore essentially linear.

Alkylation↗
PubMed1965

Studies on the metabolism of the protozoa. The molecular structure of a starch-type polysaccharide from Polytoma uvella.

1. Polytoma uvella, when grown in an acetate-containing medium, synthesizes a starch-type polysaccharide. 2. The starch differs from normal plant starches in having a lower iodine affinity, and in being relatively insoluble; this latter property makes fractionation difficult. 3. The starch contains about 16% of amylose, and on fractionation yields a branched amylopectin component that is similar in structure to a typical plant starch amylopectin.

Acetates↗