Characterization of three kinetically distinct forms of glutamate decarboxylase from pig brain

Pig brain contains three forms of glutamate decarboxylase with pI values of 5.3, 5.5 and 5.8, referred to as the alpha-, beta- and gamma-forms respectively. These forms were purified and kinetically characterized. The major synaptic form of glutamate decarboxylase (the beta-form) migrated as a single band on electrophoresis in sodium dodecyl sulphate/polyacrylamide gels with an apparent Mr of 60 000. Sodium dodecyl sulphate/polyacrylamide gel electrophoresis followed by immunoblotting with an affinity-purified antibody to the enzyme indicated a subunit Mr of 60 000 for the alpha- and gamma-forms as well. An extensive kinetic analysis, aided by an integrated equation that describes the inactivation and re-activation cycle of the enzyme, revealed that the three forms of the enzyme differ markedly in kinetic properties. The Km values for L-glutamate were 0.17, 0.45 and 1.24 mM respectively for the alpha-, beta- and gamma-forms. The Ki for 4-aminobutyrate, the first-order rate constants for inactivation by L-glutamate and 4-aminobutyrate, the rate constant for re-activation of the apoenzyme by pyridoxal 5'-phosphate and the dissociation constant for pyridoxal 5'-phosphate also differed in a similar way among the three forms; the values were in the order alpha-form less than beta-form less than gamma-form.

Binding of ATP to brain glutamate decarboxylase as studied by affinity chromatography

The interactions of two forms of porcine brain glutamate decarboxylase (beta-GAD and gamma-GAD) with the effector ATP were studied by affinity chromatography. A third form, alpha-GAD, was only slightly retarded by the affinity matrix and was eluted in the buffer wash. The interaction of GAD with the ATP affinity matrix was qualitatively similar to its interaction with free ATP as reported in previous kinetic studies. The rank order of adenine nucleotides as eluting agents and affinity ligands was ATP greater than ADP greater than AMP. GAD was also eluted by its cofactor, pyridoxal 5'-phosphate, and this was enhanced by 1 mM Pi. In contrast, a high concentration (140 mM) of Pi by itself was required to elute the enzyme. GAD remained active while bound to the affinity column and was eluted in the holoenzyme form by ATP, indicating that the affinity ligand did not bind in the active site and did not displace catalytically active cofactor from the enzyme.

Multiple forms of glutamate decarboxylase in porcine brain

Three forms of glutamate decarboxylase from hog brain (termed alpha-, beta-, and gamma-GAD) were separated by hydrophobic interaction chromatography on phenyl-Sepharose, by isoelectric focusing, and by polyacrylamide gel electrophoresis. When rechromatographed on phenyl-Sepharose, each form migrated as a single entity, indicating that the forms are not readily interconvertible. The three forms are not different-sized aggregates of one form, since all three have the same approximate molecular weight (100,000) as determined by Sephadex G-200 chromatography. The pIs of the three forms separated by phenyl-Sepharose were determined by isoelectric focusing. The values obtained (5.3, 5.5, and 5.8 for alpha-, beta-, and gamma-GAD, respectively) were comparable to the pIs of the three peaks of activity observed upon focusing of enzyme that had been subjected to phenyl-Sepharose chromatography. These results indicate that phenyl-Sepharose chromatography and isoelectric focusing separate the same three components. When synaptosomal extracts were analyzed by phenyl-Sepharose chromatography without intervening purification steps, all three forms were present, but the proportion of beta-GAD was somewhat higher and that of gamma-GAD somewhat lower than in the usual preparations.

Purification and characterization of a DNA polymerase-template complex in mouse ascites tumor cells

A DNA polymerase-template complex found in mouse Erhlich ascites tumor cells was purified by twice discontinuous gradient centrifugations and agarose gel filtration. After purification, the specific activity of the complex increased about 500-fold. The size of the complex was found to be 510,000 daltons. The shape of the complex was globular under electron microscope. Its diameter was between 100-110 A. The complex was isolated into two main enzyme proteins and a homogeneous DNA template by DEAE cellulose chromatography. The main enzyme had a molecular weight of 300,000 daltons and a sedimentation coefficient of 9.5s. The endogenous template DNA showed a single zone in polyacrylamide gel electrophoresis analysis. The sedimentation coefficient was determined to be 3.8s.

Effectiveness of intermediate-dose methotrexate and high-dose 5-fluorouracil as sequential combination chemotherapy in refractory breast cancer and as primary therapy in metastatic adenocarcinoma of the colon

Many studies reported the pretreatment with methotrexate followed by 5-FU resulted in the greatest tumor cell killing. Our preliminary laboratory studies confirmed the possibility of drug synergism in the L1210 cell line, but not in human bone marrow cells. Thirteen patients with metastatic adenocarcinoma of the breast and seven patients with metastatic adenocarcinoma of the colon were treated with an innovative approach in which methotrexate preceded 5-FU administration in an attempt to cause drug synergism and prevent drug antagonism. All patients with breast cancer and two patients with colon cancer had been extensively pretreated with multiple drugs. Of the cancer patients so treated, three (23%) with breast cancer and two (28%) with colon cancer demonstrated objective tumor response. In addition to these patients, six (46%) with breast cancer and three (43%) with colon cancer demonstrated subjective improvement as manifested by total pain relief and reduction in CEA titer. The preliminary results reported in this study suggest that sequential utilization of intermediate doses of methotrexate, followed by high doses of 5-FU, is an effective combination chemotherapy for patients with breast and colon malignancies.

Digital filtering of on-line evoked potentials

Evoked potentials recorded automatically at frequent intervals are a useful adjunct for monitoring head injury patients; however, unaveraged residual noise due to patient movement and synchronization of th- stimulus to harmonics of the line frequency is sometimes present. A frequency analysis was performed on 23 records with varying degrees of unaveraged noise and the results were used to design a digital filter. The frequency content of the records analyzed was largely contained in a band from D.C. to 200 Hz. A zero phase shift lowpass digital filter with a cutoff frequency of 200 Hz eliminated the majority of noise. Despite the low frequency content, a wide-band amplifier is still required to avoid waveform distortion, particularly latencies. Digital filters can then be applied without causing distortion.

Increased proportion of active sheep erythrocyte rosette-forming lymphocytes and plasma rosette enhancement in sarcoidosis

We examined blood lymphocyte subpopulations in 20 patients with sarcoidosis, 37 patients with other diseases, and 51 normal subjects. The B-lymphocytes were identified by the presence of surface immunoglobulin or B-lymphocyte-associated antigen. Lymphocytes were also centrifuged with sheep erythrocytes for 5 min at room temperature at 200 g, and rosette formation was assayed immediately (active E-rosette-forming T-lymphocytes) or after 60-min incubation at 4 degrees C (total T-lymphocytes). The B-lymphocytes counts did not differ among the groups. The proportions of total E-rosette-forming T-lymphocytes and active E-rosette-forming T-lymphocytes were increased in the sarcoid patients, whereas absolute counts of both types of E-rosette-forming T-lymphocytes were not different from control counts. Active E-rosette-forming T-lymphocytes showed an inverse correlation with serum concentration of angiotensin-1-converting enzyme, a probable indicator of the disease activity. Incubation of normal lymphocytes with sarcoid plasma increased the proportion of active E-rosette-forming T-lymphocytes. This plasma rosette enhancement was correlated with the number of active E-rosette-forming T-lymphocytes in the blood from which the plasma was separated. These results suggest that a factor in sarcoid plasma affects the number of active E-rosette-forming T-lymphocytes and that high numbers of these cells are associated with disease stability.