Retardation of thermal and urea induced inactivation of alpha-chymotrypsin by modification with carbohydrate polymers

Modification of enzymes by means of covalent coupling using soluble polymers results in enzymes which retain high biological activity and display resistance to denaturants, high temperature and chaotropic agents. Alpha-chymotrypsin, which has a potential for use in industrial applications, was covalently modified by reductive alkylation using polymeric sucrose (OSP, molecular weight 70 and 400 kDa), dextran (73 and 250 kDa) and carboxymethyl cellulose (CMC, approximately 12 kDa). The derivatives retained around 50-80% activity depending on the polymer used and the extent of modification. At the same time, they displayed better thermotolerance than their native counterpart with 4-14 degrees C higher T50 values. During thermal inactivation, both the native and modified enzymes showed biphasic inactivation kinetics. Half-life of modified enzymes were 2-66-fold greater for the first phase and 5-250-fold greater than the native for the second phase of inactivation. The activation free energy of inactivation of alpha-chymotrypsin coupled to polymeric sucrose (400 kDa) was 112.85 kJ/mol for the first phase and 114.71 kJ/mol for the second phase, whereas in the case of the native enzyme, the value for the first phase was 101.55 kJ/mol and 103.42 kJ/mol for the second phase. The activation free energy of inactivation (deltaG*), as well as the activation enthalpy values (deltaH*) of all the modified enzymes were greater than those of the native enzyme, which is an indication of stabilization of the protein and a retardation of inactivation that is usually accompanied by unfolding under thermal and chemical stress. The stability of modified alpha-chymotrypsin is in the following order: OSP 400-C > OSP 70-C > CMC-C > Dextran 73-C = Dextran 250-C.

Modulation of stability properties of bovine trypsin after in vitro structural changes with a variety of chemical modifiers

Controlled chemical modification of enzymes, targeting groups not involved in the active site, can lead to modified catalysts that are intrinsically more efficient and resistant to heat and denaturing agents. Bovine pancreatic trypsin was covalently modified up to 75-85% with monomeric glutaraldehyde (MGA), polymeric glutaraldehyde (PGA), oxidized sucrose and oxidized sucrose polymers (OSP 70 and OSP 400). Virtually no loss in activity occurred upon modification. Temperature optima of trypsin shifts from 45-76 degrees C and T50 from 54-76 degrees C for the best modified sample made with OSP. The efficiency of the modifiers in stabilization was ranked in the order: OSP 400-T > OSP 70-T > PGA-T > MGA-T > Sucrose-T. Half-life of modified enzymes also followed the same trend. Both stabilization factor and t1/2 decreased with increasing temperatures. The free energy of activation for inactivation delta(deltaG*) varies from 12-20 kJ/mol and the activation enthalpy delta(deltaH*) of the modified trypsin by 80-120 kJ/mol indicating stabilization. Inactivation of modified trypsin by urea is less noticeable. The character of the two-step inactivation process of trypsin changes with the degree of stabilization in that the duration of phase I one increased noticeably as stabilization increases. Native trypsin fluoresces less intensely showing a red shift under the influence of denaturation. Such a fluorescence change is not so obvious for the modified enzymes indicating conformational stability acquired by modification.

Evaluation of a miniaturized thermal biosensor for the determination of glucose in whole blood

A miniaturized thermal biosensor has been evaluated as part of a flow-injection analysis system for the determination of glucose in whole blood. Glucose was determined by measuring the heat evolved when samples containing glucose passed through a small column with immobilized glucose oxidase and catalase. Samples of whole blood (1 microliter) can be measured directly, without any pretreatment. The correlation in the response between the thermal biosensor, the Reflolux S meter (Boehringer Mannheim), the Granutest 100 glucose test kit (Merck Diagnostica) and the Ektachem (Kodak) instrument was evaluated. The influence of the hematocrit value and of possible interferences is reported. The correlation measurements show that the thermal biosensor calibrated with aqueous glucose standards generally gives lower values on blood glucose than the reference methods calibrated for serum or blood measurements. Mean negative biases range from 0.53 to 1.16 mmol/l. Differences in sample treatment clearly complicate comparisons and the proper choice of reference method. There was no influence from substances such as ascorbic acid (0.11 mmol/l), uric acid (0.48 mmol/l), urea (4.3 mmol/l) and acetaminophen (0.17 mmol/l) on the response to 5 mmol/l glucose. The hematocrit value does not influence the glucose determination, for hematocrit values of between 13 and 53%.

Personality and depression in Parkinson's disease

The Parkinson's disease (PD) patient has been characterized as having a distinctive personality with introverted features. These personality traits are said to predate motor symptoms and are theorized to serve as a subtle clue to latent PD. To examine this hypothesis, we compared remote and current personality features in 35 PD subjects and 35 controls. Subjects' spouses completed a personality inventory (PI) characterizing patients' premorbid and current status. The premorbid PI of PD subjects differed from that of controls in being more "quiet," "generous," "cautious," and "even-tempered," and less "flexible." The characterization of the PD subjects' current personality differed greatly from reported premorbid personality features, i.e., significant change in 13 of 24 PI items. Personality inventory responses regarding both the PD subjects' premorbid and current personality correlated to symptoms of depression and disease severity. Cognition, tobacco use, alcohol consumption, and rural versus urban residency did not correlate with PI responses. We conclude that PD patients are apt to be viewed as introverts premorbidly, and, with disease onset, more striking personality changes are recognized. These perceptions appear to be closely linked to depressed affect and correlate with motor impairment to a lesser extent.

Serial nonenhancing magnetic resonance imaging scans of high grade glioblastoma multiforme

Magnetic resonance imaging (MRI) from clinical experience has proven to be superior to all other diagnostic imaging modalities, including computed tomography (CT) in the detection of intracranial neoplasms. Although glioblastoma multiforme presents a challenge for all diagnostic imaging modalities including MRI, MRI is paramount to CT in detecting subtle abnormal water accumulation in brain tissue caused by tumor even before there is disruption of the blood brain barrier. Currently, clinical research and investigational trials on nonionic gadolinium contrast agents have proven that nonionic gadolinium HP-DO3A (ProHance) contrast agents have lower osmolality and greater stability, which make them superior compounds to gadolinium diethylenetriamine-pentacetic acid (Gd-DTPA). Therefore, the nonionic gadolinium contrasts have been safely administered more rapidly, in higher or multiple doses for contrast enhanced MRI without adverse side effects or changes in serum iron or total bilirubin, and the intensity of the area of enhancement and number of lesions detected were superior to that of Gd-DTPA (Magnevist) at the standard dose (0.1 mmol/Kg). Perhaps if the nonionic gadolinium contrast agent, ProHance, had been approved by the Food and Drug Administration (FDA) when this MRI was performed in 1990 it would have aided in providing contrast enhancement and visualization of the tumor lesion to assist in patient diagnosis and management. Magnetic resonance imaging also provides unique multiplanar capabilities that allow for optimal visualization of the temporal and occipital lobes of the brain without bone interference.(ABSTRACT TRUNCATED AT 250 WORDS)

Magnetic resonance imaging of an adult with the Dandy-Walker syndrome

A 30-year-old retired veteran was asymptomatic for two decades; he had carried out normal everyday living activities and was self-supporting. It was not until he was struck by an automobile, which resulted in head trauma, that the Dandy-Walker syndrome was incidentally discovered by computed tomography. Most patients with the Dandy-Walker syndrome or malformation are infants and seldom live into adulthood. Therefore, this patient is one of the very few patients with this malformation who remained in a state of cerebrospinal fluid compensation and lived to adulthood.The head trauma he received in the accident is believed to have activated neurological deficits, visual impairment, and diplopia. Although magnetic resonance imaging revealed severe hydrocephalus and lobar holoprosencephaly, the patient had no symptoms of increased intracranial pressure and no craniofacial deformities except for macrocephaly, and was capable of performing everyday living activities adequately.

Sensory motor neuropathy associated with AIDS

Clinical, laboratory, and pathologic observations in six patients with sensory motor peripheral neuropathy associated with the acquired immunodeficiency syndrome (AIDS) are presented. Blood and urine testing failed to reveal other causes for peripheral neuropathy. Distinctive CSF findings included elevated human immunodeficiency virus-specific indices. Peripheral nerve pathology confirmed the results of electrodiagnostic studies and revealed axonal loss and demyelination. Epineurial and endoneurial mononuclear infiltrates were present in three patients, and in one with early neuropathy, retroviral-like particles were present in peripheral nerve axoplasm. The findings indicate that in some patients with AIDS, neuropathy may be the direct result of a viral insult, although the causes are likely multifactorial.