Peptide bound hypohydroxyprolinuria in Handigodu Disease: a familial syndrome of spondylo epi(meta)physeal dysplasia

Handigodu Disease (HD) is disorder of the osteoarticular system prevalent in few villages of two districts of the state Karnataka in southern India. 24 hrs urinary excretions of proline (Pro) and 4-hydroxyproline (Hyp) were analyzed by HPLC. Decreased peptide bound Hyp excretions (mumole/24 hrs) were found in patient group when compared with controls (Nonaffected; 113.02 +/- 67.96, Type-I; 36.22 +/- 20.76, Type-II; 45.74 +/- 14.95, Type-III; 40.46 +/- 22.68) and without significant difference in Pro excretions. Significant increased peptide bound Pro to Hyp ratio were found in patient group compared to control (Nonaffected n=63: 2.02 +/- 1.65, Type-I n=18: 3.144 +/- 1.42, Type-II n=28: 4.21 +/- 1.95, Type-III n=8: 8.60 +/- 6.55). 24 hrs urinary excretions of deoxypyridinoline (DPD) crosslinks were found without significant difference among affected and control, hence HD ruled out from general bone reduction. These results suggest hypohydroxyprolinuria may be because of reduced bone turnover or defective hydroxylation of prolyl residues during post translational modification of collagen biosynthesis.

Alterations in neurofilament protein(s) in human leprous nerves: morphology, immunohistochemistry and Western immunoblot correlative study

Using a specific antibody (SMI 31), the state of phosphorylation of high and medium molecular weight neurofilaments (NF-H and NF-M) was studied in 22 leprous and four nonleprous human peripheral nerves by means of immunohistochemistry, sodium dodecyl sulfate-poly acrylamide gel electrophoresis (SDS-PAGE) and Western immunoblot (WB). The results thus obtained were compared with morphological changes in the respective nerves studied through light and electron microscopy. Many of the leprous nerves showing minimal pathology revealed lack of or weak staining with SMI 31, denoting dephosphorylation. Remyelinated fibres stained intensely with SMI 31 antibody. The WB analysis of Triton X-100 insoluble cytoskeletal preparation showed absence of regular SMI 31 reactive bands corresponding to 200 and 150 kDa molecular weight (NF-H and NF-M, respectively) in 10 nerves. Three of the 10 nerves revealed presence of NF protein bands in SDS-PAGE but not in WB. Presence of additional protein band (following NF-M) was seen in four nerves. Two nerves revealed NF-H band but not NF-M band and one nerve showed trace positivity. In the remaining five nerves presence of all the three NF bands was seen. Thus, 77.3% (17/22) of human leprous nerves studied showed abnormal phosphorylation of NF protein(s). The ultrastructural study showed abnormal compaction and arraying of NF at the periphery of the axons in the fibres with altered axon to myelin thickness ratio (atrophied fibres) as well as at the Schmidt-Lantermann (S-L) cleft region. Such NF changes were more pronounced in the severely atrophied axons suggesting a direct correlation. The observed well-spaced NF in the remyelinated fibres under ultrastructural study was in keeping with both intense SMI 31 staining and presence of NF triplet bands seen in WBs in four of leprous nerves that showed a large number of regenerating fibres suggesting reversal of changes with regeneration. Findings in the present study suggest that atrophy, that is, the reduction in axonal calibre and paranodal demyelination, seen in leprous nerves may result from dephosphorylation of NF-H and NF-M proteins.

Cdk5 and MAPK are associated with complexes of cytoskeletal proteins in rat brain

Neurofilament proteins, the major cytoskeletal components of large myelinated axons, are highly phosphorylated by second messenger-dependent and -independent kinases. These kinases, together with tubulins and other cytoskeletal proteins, have been shown to bind to neurofilament preparations. Cdk5 and Erk2, proline-directed kinases in neuronal tissues, phosphorylate the Lys-Ser-Pro (KSP) repeats in tail domains of NF-H, NF-M, and other axonal proteins such as tau and synapsin. In neurofilament and microtubule preparations from rat brain, we demonstrated by Western blot analysis that cdk5, a neuronal cyclin dependent kinase and Erk1/2 were associated with complexes of NF proteins, tubulins and tau. Using P13(suc1) affinity chromatography, a procedure known to bind cdc2-like kinases in proliferating cells with high affinity, we obtained a P13 complex from a rat brain extract exhibiting the same profiles of cdk5 and Erk2 bound to cytoskeletal proteins. The phosphorylation activities of these preparations and the effect of the cdk5 inhibitor, butyrolactone, were consistent with the presence of active kinases. Finally, during a column fractionation and purification of Erk kinases from rat brain extracts, fractions enriched in Erk kinase activity also exhibited co-elution of phosphorylated NF-H, tubulin, tau and cdk5. We suggest that in mammalian brain, different kinases, their regulators and phosphatases form multimeric complexes with cytoskeletal proteins and regulate multisite phosphorylation from synthesis in the cell body to transport and assembly in the axon.

Expression of p67 (Munc-18) in adult human brain and neuroectodermal tumors of human central nervous system

p67 (Munc-18), is a neuron-specific protein of 67 kDa, known for its ability to bind with syntaxin and also to copurify with neuronal cdc2-like kinase. Earlier, in situ hybridization and immunocytochemical analysis of rat trigeminal ganglion and hippocampal cells demonstrated the specific localization of p67 in nerve cells and its rich distribution in axons. In the present study, we have looked for p67 expression in normal human brain and various neuroectodermal tumors. Immunohistochemical and Western immunoblot analysis of normal human brain tissue using antibodies against the N- and C-termini of p67 demonstrated the specific localization of this protein in postmitotic neurons but not in glia. Among neuroectodermal tumors, expression of p67 was observed in 100% of the tumors of neuronal origin studied, especially in the mature neuronal cell population of these tumors. Western immunoblot analysis of non-neuronal neuroectodermal tumors failed to reveal the expression of this protein in majority of cases. However, in gliomas and meningiomas, mild cytoplasmic immunohistochemical staining of neoplastic cells was noted in 64.7% and 25% of cases, respectively. Observed mild immunohistochemical staining of these tumors could be due to immunoreactivity to low molecular weight degraded products of p67, as seen on Western blot. The findings suggest that p67, by virtue of its ability to be expressed in postmitotic neurons of adult human brain and in tumors of neuronal origin, may serve as a molecular tool to understand the growth and differentiation of the nervous system in general.

Characterization of the phosphorylation sites of human high molecular weight neurofilament protein by electrospray ionization tandem mass spectrometry and database searching

Hyperphosphorylated high molecular weight neurofilament protein (NF-H) exhibits extensive phosphorylation on lysine-serine-proline (KSP) repeats in the C-terminal domain of the molecule. Specific phosphorylation sites in human NF-H were identified by proteolytic digestion and analysis of the resulting digests by a combination of microbore liquid chromatography, electrospray ionization tandem (MS/MS) ion trap mass spectrometry, and database searching. The computer programs utilized (PEPSEARCH and SEQUEST) are capable of identifying peptides and phosphorylation sites from uninterpreted MS/MS spectra, and by use of these methods, 27 phosphopeptides and their phosphorylated residues were identified. On the basis of these phosphopeptides, 38 phosphorylation sites in human NF-H were characterized. These include 33 KSP, lysine-threonine-proline (KTP) or arginine-serine-proline (RSP) sites and four unphosphorylated sites, all of which occur in the KSP repeat domain (residues 502-823); and one threonine phosphorylation site observed in a KVPTPEK motif. Six KSP sites were not characterized because of the failure to isolate and identify corresponding phosphopeptides. Heterogeneity in serine and threonine phosphorylation was observed at three sites or deduced to occur at three sites on the basis of enzyme specificity. As a result of the phosphorylated motifs identified (KSPAKEE, KSPVKEE, KS/TPEKAK, KSPEKEE, KSPVKAE, KSPAEAK, KSPPEAK, KSPEAKT, KSPAEVK, and KVPTPEK), human NF-H tail domain is postulated to be a substrate of proline-directed kinases. The threonine-phosphorylated KVPTPEK motif suggested the existence of a novel proline-directed kinase.

Type Ib glycogenosis

Type Ib glycogenosis is a rare glycogen storage disorder resulting from a defect in the enzyme, glucose-6-phosphatase microsomal translocase. We report a case of Type Ib glycogenosis in an 18 month-old male child who presented with a history of hypoglycemic seizures and recurrent infections and had a massive hepatomegaly, recurrent hypoglycemia, hyperuricemia, hypertriglyceridemia, neutropenia and fasting lactacidemia which decreased sharply on glucose administration.

Arginase deficiency

Hyperargininemia due to arginase deficiency is a rare, inherited, urea cycle disorder. We report a case of arginase deficiency in a 5-year old boy presenting with mild hyperammonemia, hyperargininemia, and dibasic aminoaciduria.

A study of serum prolactin and plasma human growth hormone in male alcoholics

Serum levels of prolactin (PRL) and Human Growth Hormone (HGH) were assayed in 38 male alcoholics and 24 male control subjects using radioimmunoassay (RIA) technique. Biochemical parameters of hepatic function and severity of withdrawal state were also assessed. Significantly elevated values of plasma HGH were found in alcoholics as a group. Nineteen percent and eight percent of the patient had elevated serum PRL and HGH levels respectively. Evidence of advanced liver disease was scant and withdrawal symptoms were by and large mild. The findings indicate a dysfunction in hypothalamic adenohypophyseal axis in a subgroup of alcoholics.

Inhibition of neuronal cyclin-dependent kinase-5 by staurosporine and purine analogs is independent of activation by Munc-18

Neuronal cdk5 can phosphorylate certain lys-ser-pro (KSP) motifs of neurofilaments and tau protein in the nervous system. We have immunoprecipitated the cdk5 from rat brain using a polyclonal antibody raised against the C-terminus of cdk5. The immunoprecipitate has phosphorylated a KSPXK peptide analog of NF-H, as well as histone H1 and a bacterially expressed rat NF-H protein. The kinase activity was inhibited by staurosporine, isopentanyladenine and olomoucine in a dose dependent manner. Kinetic studies indicated Ki values of 39 nM, 38 microM and 8 microM, respectively for staurosporine, isopentanyladenine and olomoucine. The inhibition by staurosporine was non-competitive with respect to phosphoryl acceptor acceptor substrates. Western blot analysis of the immunoprecipitate showed both cdk5 and p67 (Munc-18), a putative regulator molecule of the kinase. Addition of p67 fusion protein enhanced the kinase activity of the immunoprecipitate by 60% above the basal activity. P67 elevated Ki values for both staurosporine and olomoucine. The degree of inhibition at high concentrations of these inhibitors was unaltered by exogenous p67 indicating a lack of competitive interactions with p67. The high affinity of staurosporine for cdk5 suggests that cdk5 may be one of the targets for the neurotropic effect of staurosporine.

GM2 gangliosidoses: a review of cases confirmed by beta-N-acetylhexosaminidase assay

The inborn errors of GM2 ganglioside metabolism cause GM2 ganglioside to accumulate within the lysosomes of the nerve cells. The majority of the patients are infants with the Tay-Sachs form of the disease associated with a severe deficiency of beta-N-Acetylhexosaminidase A (hexosaminidase A). Both Hexosaminidase A and B are deficient in Sandhoff disease. The serum total hexosaminidase and the percentage of hexosaminidase A and B were estimated in 449 patients who presented with progressive mental-motor retardation. Three cases of Tay-Sachs disease and two cases of Sandhoff disease were detected. They presented with exaggerated startle response to acoustic stimuli, seizures, optic atrophy and retinal cherry red spots in addition to psychomotor retardation. One case of Sandhoff disease had hepatosplenomegaly and skeletal deformities.

Neuronal cyclin-dependent kinase-5 phosphorylation sites in neurofilament protein (NF-H) are dephosphorylated by protein phosphatase 2A

Neurofilament (NF) protein [high molecular mass (NF-H)] is extensively phosphorylated in vivo. The phosphorylation occurs mainly in its characteristic KSP (Lys-Ser-Pro) repeat motifs. There are two major types of KSP motifs in the NF-H tail domain: KSPXKX and KSPXXX. Recent studies by two different laboratories have demonstrated the presence of a cdc2-like kinase [cyclin-dependent kinase-5 (cdk5)] in nervous tissue that selectively phosphorylates KSPXKX and XS/TXK motifs in NF-H and lysine-rich histone (H1). This article describes the identification of phosphatases dephosphorylating three different substrates: histone (H1), NF-H in a NF preparation, and a bacterially expressed C-terminal tail domain of NF-H, each containing KSPXKX repeats phosphorylated in vitro by cdk5. Among various phosphatases identified, protein phosphatase (PP) 2A from rabbit skeletal muscle appeared to be the most effective phosphatase in in vitro assays. Three phosphatase activity peaks--P1, P2, and P3--were partially purified from frozen rat spinal cord by ion exchange and size exclusion column chromatography and then characterized on the basis of biochemical, pharmacological, and immunochemical studies. One of the three peaks was identified as PP2A, whereas the others were mixtures of both PP2A and PP1. These three peaks could dephosphorylate cdk5-phosphorylated 32P-histone (H1), 32P-NF-H in the NF preparation, and 32P-NF-H tail fusion protein. These studies suggest the involvement of PP2A or a PP2A-like activity in the regulation of the phosphorylation state of KSPXKX motifs in NF-H.

Molecular characterization of a neuronal-specific protein that stimulates the activity of Cdk5

Cyclin-dependent kinase, Cdk5, has been identified in neural tissue in connection with neurofilament and tau protein phosphorylation. This report describes the characterization of a 62-kDa protein that copurifies with Cdk5 from rat spinal cord homogenates. Dissociation of the protein from neural Cdk5 is concomitant with a reversible loss in kinase activity. Amino acid sequence information from tryptic peptide fragments was used to clone the complementary DNA from rat brain. A single full-length cDNA was characterized coding for a 67.5-kDa protein (p67). Exogenously expressed p67 stimulated Cdk5 kinase activity in vitro in a dose-dependent manner and when presented as an affinity matrix, selectively adsorbed Cdk5 from a cleared rat brain homogenate. In situ hybridization analysis of E18 rat embryos and adult rat brain demonstrated that p67 transcript expression is restricted to neural tissue. Immunohistochemical staining with an amino-terminal peptide-specific antibody further indicated that p67 is exclusively expressed in neurons. Localization in vivo and in cultured rat hippocampal neurons showed that p67 is highly enriched in axons. We propose that p67, by virtue of its regulation of Cdk5, participates in the dynamics of axonal architecture through the modulation of phosphorylation of cytoskeletal components.

Disulfiram lowers Ca2+, Mg(2+)-ATPase activity of rat brain synaptosomes

The chronic administration of disulfiram (DS) to rats resulted in significant decrease of synaptosomal Ca2+, Mg(2+)-ATPase activity. In vitro studies indicated that DS (ID50 = 20 microM) produced a dose-dependent inhibition of Ca2+, Mg(2+)-ATPase. However, diethyldithio-carbamate, a metabolite of DS, failed to modify Ca2+, Mg(2+)-ATPase activity, implying that the decrease in ATPase activity in DS administered rats was due to the effect of parent compound. The DS-mediated inhibition (48%) of ATPase activity was comparable with a similar degree of inhibition (49%) achieved by treating the synaptosomal membranes with N-ethylmaleimide (ID50 = 20 microM) in vitro. Furthermore, the inhibition by DS was neither altered by washing the membranes with EGTA nor reversed by treatment with sulfhydryl reagents such as GSH or dithiothreitol. About 74% and 68% decrease of synaptosomal Ca2+, Mg(2+)-ATPase specific activity was observed when treated with DS (30 microM) and EGTA (100 microM) respectively. The remaining 25-30% of total activity is suggested to be of Mg(2+)-dependent ATPase activity. This indicates that both these drugs may act on a common target, calmodulin component that represents 70-75% of total Ca2+, Mg(2+)-ATPase activity. Therefore, DS-mediated modulation of synaptosomal Ca2+, Mg(2+)-ATPase activity could affect its function of maintaining intracellular Ca2+ concentration. This could contribute to the deleterious effects on CNS.

Viral antibodies in recent onset, nonorganic psychoses: correspondence with symptomatic severity

A parallel of generalized viral infection with psychiatric symptoms has been reported in nonorganic psychotic disorders. The patients concerned had been ill for long periods and some of them had been readmitted. In order to determine the presence of viral infection at the very onset of the psychosis, antibodies in blood and cerebrospinal fluid (CSF) to six viruses [cytomegalovirus (CMV), herpes simplex (HSV) Type 1, mumps, measles, varicella zoster virus (VZV), and Japanese encephalitis virus (JEV)] were assayed in 35 psychotic patients [14 schizophrenics; 13 manic patients; and 8 patients with psychosis not otherwise specified (NOS)] within 1 month of onset of illness. Ten (28.6%) patients had a diagnostic (fourfold) change in the antibody titer in the paired serum and/or CSF samples (drawn at 2-week intervals) and another 10 had high titers (above 2 SDs from the mean in 35 control subjects). The striking temporal correlation with the initial severity and resolution of psychopathology by 2 weeks on the Brief Psychiatric Rating Scale (BPRS) suggests a causally significant, currently active viral infection in these 20 cases.

Effect of disulfiram administration on rat brain glutathione metabolism

Chronic administration of disulfiram (DS) to rats was found to affect glutathione (GSH) metabolism. Glutathione was measured in the rat brain following DS administration. Reduced glutathione was decreased significantly (1.52 +/- 0.3 mumol/g; p < 0.001), with a concomitant increase in oxidised glutathione (GSSG) content (0.12 +/- 0.013 mumol/g; p < 0.001) in the brain as a consequence of DS treatment. However, total glutathione (GSH + GSSG) content of the experimental group did not show any appreciable change. Similar changes were observed in the liver following chronic DS treatment. Brain glutathione reductase (GR) activity was found to be significantly depleted (100 +/- 0.16 mumol/min/mg protein), but glutathione peroxidase (GP) activity was not affected in rats chronically treated with DS. It is reported that the treatment with DS decreases the GSH content, with a concomitant increase in GSSG level, and perturbs the GSH/GSSG redox status, inducing an oxidative stress on the brain. Glutathione reductase implicated in maintaining GSH/GSSG homeostasis by replenishing GSH is also affected by DS potentiating the oxidative damage of the tissue. This effect of DS on glutathione metabolism in the brain would explain some of its known neurotoxic effects.

cdc2-like kinase from rat spinal cord specifically phosphorylates KSPXK motifs in neurofilament proteins: isolation and characterization

A protein kinase that phosphorylates a specific KSP sequence [K(S/T)PXK], which is abundant in high molecular weight neurofilament (NF) proteins, was identified and isolated from rat spinal cord. Characterization of this enzyme activity revealed a close relationship with p34cdc2 kinase with respect to its molecular mass (32.5 kDa by SDS/PAGE) and substrate specificities. It could phosphorylate a synthetic peptide analog of the simian virus 40 large tumor antigen, reportedly a specific substrate for p34cdc2 kinase. Histone (H1) and peptide analogs of the KSP sequence present in the C-terminal end of rat and mouse neurofilament proteins were phosphorylated. This kinase did not phosphorylate alpha-casein and peptide substrates of other known second messenger-dependent or -independent kinases. Dephosphorylated rat NF protein NF-H was strongly phosphorylated by the purified enzyme; NF proteins NF-M and native NF-H, but not NF-L, were slightly phosphorylated. Studies on synthetic peptide analogs of KSP repeats with substitution of specific residues, known to be present in the C-terminal regions of NF-H, revealed a consensus sequence of X(S/T)PXK, characteristic of the p34cdc2 kinase substrate. On Western blots, the enzyme was immunoreactive with antibody against the C-terminal end of cdc2 kinase (mouse) and neuronal cdc2-like kinase from rat but not with an antibody against the conserved PSTAIRE region of the p34cdc2 kinase. The antibody against the C-terminal end of cdc2 kinase could immunoprecipitate (immunodeplete) the purified kinase activity. Since the adult nervous system is composed primarily of postmitotic cells, the present observations indicate a nonmitotic role for this cdc2-like kinase activity. The effective phosphorylation of NF-H by this kinase suggests a function in axonal structure.

Effect of disulfiram administration on brain tryptophan, serotonin and peripheral tryptophan content

The prophylactic deterrent effect of disulfiram (DS) has been attributed to its ability to exacerbate sympathetic function. Though there are reports to indicate that DS administration could as well affect the neurotransmitter metabolism, few reports implicate the possibility of central nervous system (CNS) mediated anticraving effect of the drug. The present study involving the oral administration of DS to rats for 45 days has clearly shown a significant increase in 5-HT (815.4 +/- 74.7 ng/g, P < 0.01) and 5-HIAA (506.1 +/- 86.3 ng/g, P < 0.02) contents in brain when compared to control rats. The observed increase in 5-HT and 5-HIAA content was found to correlate (zeta = 0.89) with the concomitant increase in brain tryptophan content (4.15 +/- 1.05 nmol/g, P < 0.001) following DS administration. Further, the study on peripheral tryptophan content has shown an increase in both total and free fraction (ultrafiltrate) of plasma, which in turn was found to have an inverse relationship (zeta = -0.94, P < 0.05) with the decrease in liver tryptophan content following DS administration. Thus the observed increase in brain 5-HT level is attributed to the ability of DS to mobilise peripheral tryptophan for 5-HT synthesis in CNS. As there are reports to imply the hyposerotonergic function as responsible for craving, the present findings, that DS could enhance the 5-HT metabolism in brain, may partially explain the CNS mediated anticraving effect of DS.

Diazepam- and chlordiazepoxide-mediated increases in erythrocyte aldehyde dehydrogenase activity and its possible implications

Erythrocyte ALDH activity was assayed in alcoholic (n = 70) and nonalcoholic (n = 40) subjects. In general, alcoholics without any prior medications (n = 57) were found to have a decreased ALDH activity (mean +/- SD: 3.38 +/- 1.7 mU; p less than 0.001) as compared to control group (5.10 +/- 1.57 mU). However, a group of alcoholics who were detoxified with benzodiazepines (n = 13) prior to blood collection for enzyme assay were found to have higher ALDH activity (4.92 +/- 2.46 mU; p less than 0.05) as compared to alcoholics who were not detoxified. In vitro experiments demonstrated that both diazepam (DZM) and chlordiazepoxide (CDP) could activate the ALDH. The magnitude of enzyme activation by DZM and CDP appear to correlate with their relative potency of tranquilizing effect. Further, the observed ability of DZM to reverse the inhibition of ALDH mediated by disulfiram may explain the biochemical basis of the reported ability of benzodiazepines (BDZ) to reduce the intensity of disulfiram ethanol reaction (DER).

Pituitary - adrenal functioning in male alcoholics

Serum adrenocorticotrophic hormone (ACTH) and Cortisol were assayed in 38 males alcoholics and 24 male control subjects using radioimmunoassay (RIA) techniques. Biochemical parameters of hepatic function, depressive symptoms and severity of withdrawal were also assessed. Thirteen percent and eleven percent of the patients and elevated serum ACTH and Cortisol levels respectively. Evidence of advance liver disease was scant and significant symptoms of depression was observed in only 14% of the patients. By and large withdrawal symptoms were mild. Two patients have clinical features suggestive ofpseudo Cushing's syndrome without hypercortisolaemia.

Phosphatase activity against neurofilament proteins from bovine spinal cord: effect of aluminium and neuropsychoactive drugs

Protein phosphatase activity associated with neurofilament (NF) rich (Triton X-100 insoluble) fraction was extracted and partially characterised by using known inhibitors of protein phosphatases such as vanadate and fluoride. Protein phosphatase activity was demonstrated with reference to the dephosphorylation of endogenous substrate, NF protein and exogenous protein substrates, casein and phosvitin. Phosphoamino acids and beta-glycerophosphate were found to be poor substrates. Further, new observations have been made regarding the in vitro inhibitory effect of aluminium and the differential effects of some of the neuropsychoactive drugs. The findings could possibly lead to studies explaining the biochemical basis of aluminium induced neurotoxicity as well as the side effects associated with the long term medication of neuropsychoactive drugs.

Effect of chronic ethanol ingestion on phosphate content of neurofilament proteins and neurofilament associated protein phosphatase in rat spinal cord

Rats were trained to drink alcohol solution by gradually increasing the ethanol content [2.5-15% (v/v)] in drinking water. After 11 months of alcohol (15% v/v) ingestion, animals were guillotined and the spinal cords were used for the preparation of neurofilaments (NF). NF triplet proteins were separated by SDS-PAGE and the phosphate contents of individual components were estimated. Results indicated a significant increase in phosphate content of 200 KD protein in alcohol fed rats (30.19 +/- 4.12 mol of phosphate/mole of protein: p less than 0.001) compared to control group (18.42 +/- 3.91 mol of phosphate/mole of protein). No significant change in the phosphate content of 150KD and 68KD components of NF were seen in experimental group. Further, the studies on NF associated protein phosphatase activity indicated a significant decrease in phosphatase activity among the alcohol fed rats (14.10 +/- 2.5 mU; p less than 0.001) against NF rich fraction as a substrate, as compared to control (20.15 +/- 2.15 mU). While the observed decrease in NF associated protein phosphatase would possibly explain the increase in phosphate content of NF proteins in alcohol fed rats, the precise mechanism of decrease in enzyme activity remains to be elucidated. Nevertheless, the change seen in phosphate content and NF associated protein phosphatase activity as a result of ethanol ingestion would possibly form the biochemical basis of some of the neuropathological changes seen in alcoholics.

Role of glutathione reductase system in disulfiram conversion to diethyldithiocarbamate

Experiments were carried out to establish the role of glutathione reductase (GR), if any, in the metabolic conversion of disulfiram (DS) to diethyldithiocarbamate (DDC). It was observed that, under standard assay conditions, whereas DS was incorporated as a substrate instead of oxidised glutathione (GSSG), the enzymes from both human liver extract and yeast sources failed to reduce the parent compound, implying that glutathione reductase perse do not reduce disulfiram. However, the incorporation of disulfiram into an assay system comprising of GSSG, NADPH and reductase resulted in DS reduction to DDC. Further, the observation, that the GR assay system devoid of either GSSG or NADPH was found to lack DS reducing ability, implies that GSH as a reaction product of GR system is responsible for the reduction of DS to DDC. The results of in-vitro experiments indicated that GSH perse could reduce DS to DDC nonenzymatically, with a stoichiometric relationship of 2:1. Thus it is inferred that GR perse do not reduce DS, whereas GSH, as an intermediary metabolite of GR system, brings about non-enzymatic reduction of DS via a sulfhydral group exchange reaction.

Phosphoserine phosphatase of human brain: partial purification, characterization, regional distribution, and effect of certain modulators including psychoactive drugs

Phosphoserine phosphatase (PSPase), a cytosolic enzyme has been purified 106 fold from human brain, by employing conventional protein purification techniques. The use of MgCl2 (10 mM) and chloroform treatment, during purification enabled the removal of non-specific proteins. The final enzyme preparation exhibited a broad pH optimum of 5.6-6.6 and could dephosphorylate both L and D enantiomers of the phosphoserine, but with different Km values for O-P-L serine (3.6 x 10(-5) M) and O-P-D serine (1 x 10(-4) M). Enzyme activity was found to be specific for phosphoserine, whereas other phosphoesters including phosphothreonine and phosphoproteins such as casein and phosvitin were found to be poor substrates. The enzyme activity was uncompetitively inhibited by L-serine. Further the PSPase activity was inhibited by vanadate, (41%), trifluoperazine (23%), chlorpromazine (34%) at an equimolar concentration of 1 mM, whereas lithium and ethanol did not influence the enzyme activity. Minor tranquilizers such as diazepam and chlordiazepoxide activated the enzyme activity to an extent of 13% and 59% respectively. In addition, species and regionwise heterogeneity was observed with respect to distribution of enzyme activity in six major areas of human, rabbit and rat brains.

Methodological aspects of aldehyde dehydrogenase assay by spectrophotometric technique

Aldehyde dehydrogenase (ALDH) activity was assayed spectrophotometrically by measuring the increase in delta A at 340 nm, as a criteria of NAD conversion to NADH in the presence of propionaldehyde. The effect of pH and substrate(s) concentration of nonenzymatic increase in absorbance at 340 nm was studied. Results indicate that the increase in absorbance at 340 nm is not entirely due to NAD conversion to NADH. It was observed that nonenzymatic interaction of NAD and aldehyde could as well result in increase in absorbance at 340 nm. The magnitude of the nonenzymatic contribution towards increase in absorbance at 340 nm is found to be pH, substrate(s) conc., and time dependent. Further, the observed nonenzymatic reaction product was found to be different from that of NADH as confirmed by u.v. spectral characteristics (lambda max. 346 nm) and its inability to activate NADH/NADPH-dependent glutathione reductase. Based on these findings, a final assay method comprising a substrate blank consisting of NAD and aldehyde, and the assay pH of 7.4 is recommended for measuring the ALDH activity. Further, under these experimental conditions the Km value of human RBC ALDH was found to be 0.59 mM for propionaldehyde substrate.

Occurrence of gamma-glutamyl transpeptidase activity in several mycobacteria including Mycobacterium leprae

gamma-Glutamyl transpeptidase (gamma-GT) activity, which catalyzes the transfer of the "gamma-glutamyl" group of gamma-glutamyl compounds to several dipeptide and amino acid acceptors, was found to be present in several mycobacteria, including M. leprae, both in cell suspensions and in cell-free sonicates. Glycyl D-amino acids were active as acceptors, particularly glycyl-D-alanine and alpha, epsilon-diaminopimelic acid, among the amino acids. Two mycobacterial isolates obtained from biopsy material of lepromatous patients also exhibited similar enzyme activity. The need for further work to delineate the possible role of gamma-GT in mycobacterial metabolism is strongly indicated.