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Biomedical subjects

K J Kramer

Publications and source records attributed to K J Kramer.

At least 91 records · Page 5Linked to original sources
PubMed1978

Silkmoth chorion proteins. Their diversity, amino acid composition, and the NH-terminal sequence of one component.

Silkmoth eggshell (chorion) proteins have been characterized by electrophoresis on sodium dodecyl sulfate and isoelectric focusing polyacrylamide gels; up to 33 and 41 components, respectively, were detected from a single chorion. Some of these components are polymorphic, being absent from chorions of certain animals. A system of nomenclature for all chorion proteins is presented, based on their separation on sodium dodecyl sulfate and isoelectric focusing gels. The chorion is enriched in glycine, alanine, cysteine, and tyrosine and poor in methionine and histidine. The proteins were fractionated into four partially overlapping groups; all four are enriched in the above amino acids, although significant differences exist. Further fractionation by isoelectric focusing of one of the above groups, s/s, yielded seven components, two of which are homogeneous both on sodium dodecyl sulfate and isoelectric focusing gels. The amino acid compositions, molecular weights, and solubility properties of the components share certain features which distinguish s/s as a group from the other three groups. The sequence of the first 67 NH2-terminal residues of a homogeneous protein purified from s/s has been determined. The protein contains a cysteine-rich tail (3 cysteines in the first 18 residues) followed by a 49-residue segment which contains only a single cysteine residue. This latter segment also contains two different tetrapeptide sequences which are each repeated, one twice and the other four times.

Amino Acid Sequence↗
PubMed1977

Bioassay for homogeneous parasporal crystal of Bacillus thuringiensis using the tobacco hornworm, Manduca sexta.

A method for determining the toxicity of Bacillus thuringiensis subsp. kurstaki parasporal crystal to the tabocco hornworm, Manduca sexta, is described. The use of both mortality and weight loss data have provided a highly sensitive and reproducible bioassay that can be used to compare relative toxicities of crystals from other subspecies as well as toxic components contained therein.

Animals↗
PubMed1977

Characterization of the entomocidal parasporal crystal of Bacillus thuringiensis.

The parasporal crystalline protoxin of Bacillus thuringiensis contains a single glycoprotein subunit that has a molecular weight of approximately 1.2 X 10(5). The carbohydrate consists of glucose (3.8%) and mannose (1.8%). At alkaline pH, the proendotoxin is apparently solubilized and activated by an autolytic mechanism involving an inherent sulfhydryl protease that renders the protoxin insecticidal. Activation generates protons, degraded polypeptides, sulfhydryl group reactivity, proteolytic activity, and insect toxicity. Chemical modification of the sulfhydryl groups inhibits the proteolytic and insecticidal activities, suggesting that cysteine residues may be present in the active site of the protein.

Amino Acids↗
PubMed1976

Purification and characterization of the carrier protein for juvenile hormone from the hemolymph of the tobacco hornworm Manduca sexta Johannson (Lepidoptera: Sphingidae).

The larval hemolymph of the tobacco hornworm, Manduca sexta, contains a carrier protein that binds specifically and with high affinity the juvenile hormone, an important regulator of insect development. This protein serves to transport the hormone and to protect it from the action of degradative enzymes during early larval stages. Using hemolymph from the last larval stage, we have isolated a pure carrier protein using acetone precipitation, gel filtration, ion exchange chromatography, and preparative isoelectric focusing. Gel filtration, polyacrylamide gel electrophoresis in sodium dodecyl sulfate, and equilibrium ultracentrifugation established that the carrier protein is a single chain polypeptide of approximately 28,000 daltons. The amino acid composition is unexceptional, and no evidence for hexosamine has been obtained. An ion exchange filter disc assay method was used to determine the formation of the complex between the carrier protein and isotopically labeled juvenile hormone. With this technique it was shown that each carrier protein binds one hormone molecule with a dissociation constant of 4.4 +/- 0.2 X 10(-7) M at 0 degrees.

Amino Acids↗
PubMed1976

Glucagon-like and insulin-like hormones of the insect neurosecretory system.

Aqueous extracts of corpus cardiacum-corpus allatum complexes of the adult tobacco hornworm Manduca sexta produced both glycogenolysis and hypoglycaemia when injected into the larval form of the same species. Application of specific radioimmuno assays to similar extracts showed also that these gland complexes contain both glucagon-like and insulin-like peptides. Further, the partially purified immunoreactive peptides had the expected biological activities. The former decreased the glycogen content of the fatbody and the latter the circulating trehalose levels in recipient animals. These results suggest the existence of hormones in these invertebrates having both biological and structural similarities to vertebrate insulin and glucagon.

Animals↗
PubMed1974

The Juvenile Hormone Binding Protein in the Hemolymph of Manduca sexta Johannson (Lepidoptera: Sphingidae).

C(18):juvenile hormone is quite soluble in water, yielding a monomeric solution greater than 10(-5) M. In vivo injection or addition of aqueous juvenile hormone to the hemolymph in vitro shows the complexation of juvenile hormone to a protein, as demonstrated by gel permeation chromatography and disc-gel electrophoresis. The protein has an apparent molecular weight of 3.4 x 10(4) and is present in the hemolymph at a concentration in the micromolar range. The binding of the hormone to the protein can be described as a simple thermodynamic equilibrium with a dissociation constant of 3 x 10(-7) M, and the protein has a much higher affinity for the hormone than for the hydrolysis products.

Journal Article↗
PubMed1974

A model of the kinetics of insulin in man.

The design of the present study of the kinetics of insulin in man combines experimental features which obviate two of the major problems in previous insulin studies. (a) The use of radioiodinated insulin as a tracer has been shown to be inappropriate since its metabolism differs markedly from that of the native hormone. Therefore porcine insulin was administered by procedures which raised insulin levels in arterial plasma into the upper physiologic range. Hypoglycemia was prevented by adjusting the rate of an intravenous infusion of glucose in order to control the blood glucose concentration (the glucose-clamp technique). (b) Estimation of a single biological half-time of insulin after pulse injection of the hormone has been shown to be inappropriate since plasma insulin disappearance curves are multiexponential. Therefore the SAAM 25 computer program was used in order to define the parameters of a three compartment insulin model. The combined insulin mass of the three compartments (expressed as plasma equivalent volume) is equal to inulin space (15.7% body wt). Compartment 1 is apparently the plasma space (4.5%). The other two compartments are extra-vascular; compartment 2 is small (1.7%) and equilibrates rapidly with plasma, and compartment 3 is large (9.5%) and equilibrates slowly with plasma. The SAAM 25 program can simulate the buildup and decay of insulin in compartments 2 and 3 which cannot be assayed directly. Insulin in compartment 3 was found to correlate remarkably with the time-course of the servo-controlled glucose infusion. Under conditions of a steady-state arterial glucose level, glucose infusion is a measure of glucose utilization. We conclude that compartment 3 insulin (rather than plasma insulin) is a more direct determinant of glucose utilization. We suggest that the combined use of glucose-clamp and kinetic-modeling techniques should aid in the delineation of pathophysiologic states affecting glucose and insulin metabolism.

Adolescent↗