An integral membrane protein form of brain L-glutamate decarboxylase: purification, characterization and its relationship to insulin-dependent diabetes mellitus

A new and novel form of L-glutamate decarboxylase (GAD; EC 4.1.1.15) was purified from whole porcine brain to apparent homogeneity by a combination of column chromatographies on DE-52, ultragel AcA 34, hydroxylapatite and Sephadex G-200, and native gel electrophoresis. The purified GAD was established as an integral membrane protein based on hydrophobic interaction chromatography and membrane extraction studies. This membrane GAD (MGAD) has a native molecular weight of 120 +/- 5 kDa and is a homodimer of 60 +/- 2 kDa. Immunoprecipitation and immunoblotting tests using the sera from insulin-dependent diabetes mellitus (IDDM) patients revealed the presence of antibodies against this newly identified MGAD in IDDM. The role of MGAD in the pathogenesis of IDDM and related autoimmune disorders is also discussed.

Purification and characterization of a novel form of brain L-glutamate decarboxylase. A Ca(2+)-dependent peripheral membrane protein

L-Glutamic acid decarboxylase (GAD) catalyzes the one-step biosynthesis of gamma-aminobutyric acid (GABA), which is widely accepted as the major inhibitory neurotransmitter in the mammalian brain. In this paper, we report the identification and purification of a new and novel form of peripheral membrane GAD (MGAD) referred to as MGADIII, using a combination of chromatography on DE52, AcA 34, hydroxylapatite and Sephadex G-200, and native gel electrophoresis. The purified MGADIII migrated as a single protein band on a native 5-25% gradient polyacrylamide gel electrophoresis and sodium dodecyl sulfate-polyacrylamide gel electrophoresis with an apparent molecular mass of 118 +/- 6 and 60 +/- 4 kDa, respectively, suggesting that it is a homodimer of 60 kDa. MGADIII was established as a Ca(2+)-dependent peripheral membrane protein based on Triton X-114 phase partitioning assay, liposome binding experiment, and membrane extraction studies. Several lines of evidence are presented to show that the association of MGADIII with membranes occurs during depolarization of nerve terminal and that this is a reversible process. Based on these results and previous findings that GAD associates with synaptic vesicles and is regulated by phosphorylation, a model for regulation of GAD in the nerve terminal is proposed.

A membrane form of brain L-glutamate decarboxylase: identification, isolation, and its relation to insulin-dependent mellitus

A membrane form of L-glutamate decarboxylase (GAD) was identified and purified to apparent homogeneity from hog brain. The purified GAD was established as an integral membrane protein by phase-partitioning assay, charge-shift electrophoresis, and chromatography on a hydrophobic interaction column. This membrane GAD has a native molecular mass of 96 +/- 5 kDa and is a homodimer of 48 +/- 3-kDa subunits. Immunoprecipitation and immunoblotting tests revealed the presence of antibodies against this membrane GAD in sera from patients with insulin-dependent diabetes mellitus. Since this form of GAD appears to be an integral membrane protein and is presumed to have extracellular domains exposed, it seems reasonable to suggest that membrane GAD is more likely than soluble GAD to be involved in the pathogenesis of insulin-dependent diabetes and related autoimmune disorders such as stiff-man syndrome.

Electrophoretically mediated microanalysis of leucine aminopeptidase in complex matrices using time-resolved laser-induced fluorescence detection

Leucine aminopeptidase, a clinically significant enzyme, was assayed in complex biological samples using a new technique termed electrophoretically mediated microanalysis. The assay was performed in capillary electrophoresis columns using time-resolved laser-induced fluorescence detection. Human serum, human urine, and Escherichia coli supernatant samples were assayed using this method. Results for serum and urine were within the ranges of expected values found in the literature. A low concentration of 6 x 10(-13) M enzyme in buffer was detected using this method. A detection limit (3 sigma) of 400 enzyme molecules in buffer was determined.

Enhancement of c-fos expression in neurons of the rat spinal cord after partial denervation: evidence for functional plasticity

c-fos immunocytochemistry was used to test a functional correlate of neuroplasticity involving nociceptive primary afferent fibers in the partially denervated adult rat spinal cord. Unilateral dorsal root ganglionectomies were made at L1-L4 (chronic side). After 3 weeks, contralateral L1-L4 ganglionectomies (acute side) were made 1 week prior to sacrifice. Two hours prior to perfusion, the animals were anesthetized and their hindlimbs were immersed in a 52 degrees C water bath for 20 s. The spinal cords were then processed for c-fos immunocytochemistry and the numbers of c-fos-immunoreactive cells determined. Following bilateral noxious thermal stimulation of the hindlimbs, the numbers of c-fos-immunoreactive cells in laminae I-II from L3 to L5 were increased by nearly twofold on the chronically deafferented side of the spinal cord (P < 0.05). This finding suggests augmented functional plasticity of nociceptive primary afferent fibers on the chronically denervated side of spinal cord. These observations are discussed with relation to recent demonstrations of enhanced calcitonin gene-related peptide immunoreactivity and possible primary afferent fiber sprouting in similar denervation models.

Ultramicro enzyme assays in a capillary electrophoretic system

This paper describes an ultramicro method for achieving enzyme assays. Enzyme saturating concentrations of substrate, coenzyme when appropriate, and running buffer were mixed and used to fill a deactivated fused-silica capillary in a capillary zone electrophoresis apparatus. The enzyme glucose-6-phosphate dehydrogenase was injected by either electrophoresis or siphoning and mixed with the reagents in the capillary by electrophoretic mixing. Enzyme activity was assayed by electrophoresing the product, reduced nicotinamide adenine dinucleotide phosphate, to the detector where it was detected at 340 nm. Under constant potential, the transport velocity of enzyme and the product was generally different. This caused product to be separated from the enzyme after it was formed. Because product formation was much faster than the rate of enzyme-product separation, product accumulated. The amount of accumulated product was inversely related to operating potential. In the extreme case, the operating potential was zero. Zero potential assays were generally carried out by electrophoresing the enzyme partially through the capillary and then switching to zero potential. This capillary was left at zero potential for several minutes to allow additional product to accumulate. After this additional amplification step, potential was again applied and the product transported to the detector. Product formed under constant potential appears as a broad peak with a flat plateau. When the voltage is switched to zero at intermediate migration distance, a peak will be observed on top of this plateau. Either the eight of the plateau or the area of the peak may be used to determine enzyme concentration. The lower limit of detection was 4.6.10(-17) mol of glucose-6-phosphate dehydrogenase.

[Effects of serotonin and norepinephrine on neuronal discharges of the nucleus tractus solitarii in medullary slices]

Effects of serotonin (5-HT) and norepinephrine (NE) on neuronal activities of the nucleus tractus solitarii (NTS) were investigated in rat medullary slice preparations. The spontaneous discharges after perfusion of slices with 5-HT (1 mumol.L-1, 3 min) were increased in 25 (58.1%), reduced in 13 (30.2%), and unchanged in 5 (11.7%) neurons. Afer perfusion of slices with NE (1 mumol.L-1, 3 min), the spontaneous discharges were reduced or ceased in 27 (62.8%), increased in 13 (30.2%), and unchanged in 3 (7.0%) neurons. Responding to both 5-HT and NE were 38 (88.4%) neurons, among which 21 were selected for studying the effect of ketanserin (a new 5-HT2 blocker). The spontaneous discharges were more increased in 10 (47.6%) and reduced in 4 (19.0%) neurons after perfusion of ketanserin+NE than after perfusion of NE alone. These results indicate that there is an interaction between 5-HT2 receptor and alpha 2 adrenoceptor at NTS level, suggesting that the central action of ketanserin may be one of its antihypertensive mechanisms.

Isolation and characterization of endogenous modulators for GABA system

Pig brain extracts from both soluble and membrane fractions were found to contain potent inhibitors for GABA synthesizing enzyme, GAD, referred to as endogenous GAD inhibitors (EGIs) and for the binding of GABA agonist, muscimol, referred to as muscimol binding inhibitors (MBIs). EGIs and MBIs were first purified through gel-filtration Bio-Gel P-2 columns, in which multiple activity peaks were observed. One of them appears to be co-eluted with either L-glutamate or GABA. However, others are clearly separated from L-glutamate or GABA. EGIs were found to be low MW (less than 1,800 dalton), heat and acid-base stable, negatively charged, non hydrophobic substances. MBIs were found to be low MW (less than 1,800 dalton) neutral or positively charged substances. MBIs had no effect on [3H]flunitrazepam (FNZP) binding, indicating that they are not endogenous benzodiazepine receptor ligands and they may act specifically on GABA binding site.

[A simple and sensitive DNA-RNA hybridization method--in situ hybridization on the nitrocellulose filter for detecting oncogene expression in tumor cells by using digoxigenin-labelled probes]

A simple and sensitive method for detecting oncogene mRNA is performed by fixing tumor cells directly onto nitrocellulose paper, followed by in situ RNA hybridization with digoxigenin-labelled oncogene probes. The human lung large cell carcinoma cell line PLA801-D95 (before and after induction of differentiation with retinoid acid) and leukemic cells from clinical patients were used as target cells. The results showed that 5000 cells were sufficient to give a positive signal for oncogene mRNA. Compared with RNA dot blot, it was found that this technique was quick, simple, sensitive and reproducible. It can be used to study gene expression in tumor cells as well as other cells.

[Long-term changes in the different types of coronary diseases treated with traditional Chinese and Western medicine]

64 cases with TCM differential types of CHD treated with TCM-WM in long term (an average of 10.5 years) were divided into four types according to deficiency of Yang [including weakness of Q1], deficiency of Yin, blood stasis and disorder of Qi and phlegm. Compared with pre-treatment 42 cases (65.62%) with TCM differential types showed improvement or no change in group I, II (clinical total effective rate 92.86%, the significantly effective rate 40.98%). While 22 cases (34.38%) with TCM differential type became aggravated or worse (clinical total effective rate 54.54%, the significantly effective rate 13.63%). The report indicated that the results in comparing group I, II with group III, IV were statistically significant; age (P less than 0.01), course of disease (P less than 0.01), impairment of myocardium (P less than 0.05), complication (P less than 0.05), ratio of deficiency of Yang (P less than 0.01), blood stasis (P less than 0.01) and high coagulation of blood (P less than 0.01). Therefore the author suggests that it is necessary to protect Yang-Qi and prevent and treat the complication of the CHD patients.

Structure and function of L-glutamate decarboxylase

Membrane bound L-glutamate decarboxylase (GAD) has been solubilized and partially purified from hog brain. The solubilized GAD appears to exist in two forms, alpha and beta, differing in their size and electrophoretic mobility. The alpha form has similar mobility as that of the soluble GAD in 7.5% and 5-25% gradient polyacrylamide gel electrophoresis suggesting that they are similar in size and charge. In addition, gene encoding for mouse brain GAD has been cloned and characterized. Mouse brain GAD cDNA consists of two DNA fragments with 1.6 and 1.0 Kb. The 1.6 and 1.0 Kb fragments contain 1657 and 974 bP, respectively. The significance of multiple forms of GAD is also discussed.

[15 years' observation and related research on diagnosis and treatment according to traditional Chinese medicine of elevated serum lipids in 54 cases of coronary disease]

The increasing rate of cholesterol (CH) of 54 cases with coronary heart disease was 33.33%. According to CH level, the authors divided them into two groups: the normal one (I) and the high one (II). By fifteen-year observation, CH of Group I kept normal, only with its triglyceride (TG) a little higher than ordinary level. But the CH and TG of Group II, which had been treated with anticholesteremic drugs, was obviously higher than Group I (P less than 0.05). In connection with identification according to TCM, both CH and TG of deficiency of Yang, and deficiency of both Yin and Yang were higher, especially TG (P less than 0.01). TG of the type of blood stasis was higher (P less than 0.01) except anticholesteremic drugs for Group II. The two groups were treated with the same combined treatment of TCM and WM. The long term effect of fifteen years in Group I was more obvious than in Group II. This showed that the treatment of high serum lipid of CHD was more difficult.