Extended shelf life of enzyme-based biosensors using a novel stabilization system

The storage stability of amperometric enzyme electrodes has been enhanced by a combination of a soluble, positively charged polymer, diethylaminoethyl (DEAE)-dextran, and a sugar alcohol, lactitol. Two different types of alcohol biosensor have been produced using the enzyme alcohol oxidase, isolated from the methylotrophic yeast Hansenula polymorpha. The first employs enzyme entrapment between two membranes with direct hydrogen peroxide amperometry at +0·65 V. The second was based on the mediated, coupled reaction with horseradish peroxidase and N-methyl phenazimiumtetracyanoquinonedimethane (NMP-TCNQ) on a graphite electrode. In both cases, addition of the stabilizers promoted a considerable increase in the storage stability of the enzyme component, as indicated by an increase in the shelf life of desiccated biosensors under conditions of thermal stress at 37°C. In addition, an L-glutamate biosensor constructed from NMP-TCNQ-modified graphite electrodes and L-glutamate oxidase also exhibited an increase in shelf life when stored, desiccated in the presence of stabilizers.     

Human insulin autoantibody fine specificity and H and L chain use

Fine specificity and H and L chain isotypes of insulin autoantibodies in sera from 11 subjects were examined. None of these 11 subjects was treated with exogenous insulin. Two patterns of fine specificity were found. In one, the autoantibodies were specific for human insulin, with a requirement for threonine at B30. The conservative substitution in pork insulin (threonine to alanine) abrogated IgG binding by these sera. Insulin autoantibodies in other sera cross-reacted with beef, pork, and human insulin; not requiring threonine at B30. Reciprocal competitive inhibition experiments showed that epitopes recognized by the human specific insulin autoantibodies were exclusively on the B chain, whereas the cross-reactive sera contain autoantibodies that recognize both the B chain and combinatorial (A and B chain) epitopes. The fine specificity of cross-reactive insulin autoantibodies are thus similar to insulin antibodies from insulin-treated subjects. When IgG subclasses and L chains of insulin autoantibodies were examined, however, restricted C region usage was found. The hierarchy was IgG3 greater than G1 greater than G2 greater than G4; with one subclass dominant in each serum, although others were used. L chain use was similarly restricted. There was no correlation between isotype and fine specificity or between H and L chain type. It is concluded that heterogeneity of insulin autoantibodies is restricted. The response is probably more oligo- or pauciclonal than insulin antibody from insulin-treated subjects.     

The phosphoenol-pyruvate branchpoint in adult Hymenolepis diminuta (Cestoda): a study of pyruvate kinase and phosphoenol-pyruvate carboxykinase.

The properties of pyruvate kinase (PK) and phosphoenol pyruvate carboxykinase (PEP CK), two enzymes that determine the preferrential accumulation of either succinate or lactate as endproducts of carbohydrate metabolism, are described in adult Hymenolepis diminuta. PK activity at Vmax and Km levels of PEP was unaffected by ATP, alanine, FDP4, OR H+ ions, but was inhibited by 50% at 6.3 mM L-lactate and 30 mM HCO3. The addition of 30 mM HCO3 increased the Km(PEP) by 6-fold but did not alter the Vmax. The inhibition of PK by HCO3 cannot be explained entirely by an effect of ionic strength, but probably represents a specific modulator-enzyme interaction. Under similar conditions PEP CK was maximally activated. Although L-lactate inhibited PEP CK (Ki(lac) = 1.8 mM), this effector may play a minor role in regulation of PEP flux. These results implicate the poise of the HCO3-:CO2 system as a major determiner of endproduct accumulation in H. diminuta.