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Biomedical subjects

H Grimminger

Publications and source records attributed to H Grimminger.

15 recordsLinked to original sources
PubMed1995

[Primary radiotherapy of nasopharyngeal carcinoma].

One hundred twenty-one patients treated for nasopharyngeal carcinoma with radiation therapy were analyzed; 85 were male, 36 were female. Twenty-one percent had tumour stage T0/T1; 32.5%, T2; 27.5%, T3; and 19%, T4. In 75% of the cases, the lymph nodes were involved. Twelve patients underwent a neck dissection. Histology showed squamous cell carcinoma in 38%, lymphoepitheloid carcinoma in 41.4%, undifferentiated carcinoma in 19%, and adenocarcinoma in 2%. Beginning in 1980, a modified radiation technique with large portals and an increase of the dose from 57.1 Gy to 61.5 Gy targe volume dose was used. Five year overall survival was 32.1%, recurrence-free survival, 30.7%; and local recurrence free survival, 45.8%. Age, sex, and T stage had no significant influence on survival. Multivariate analysis (Cox model) showed that involvement of the lymph nodes, histology, and the new irradiation technique with the higher total dose significantly influenced survival.

Adenocarcinoma↗
PubMed1979

Acetohydroxy acid synthase I of Escherichia coli: purification and properties.

Several properties of the three acetohydroxy acid synthases of Escherichia coli have been compared in crude extracts. The three enzymes can be readily distinguished from each other. Acetohydroxy acid synthase I, the product of the ilvB gene, has been purified to near homogeneity. The purification was made possible by the fact that the enzyme was maintained in buffers of a high ionic strength or in buffers containing glycerol. Density gradient centrifugation studies indicated that the enzyme exists as a dimer of subunits of similar (60,000) molecular weight in buffers containing glycerol with or without two of the cofactors. Mg2+ and thiamine diphosphate. When flavine adenine dinucleotide was added along with Mg2+ and thiamine diphosphate, an increase in the rate of sedimentation occurred that was thought to be due to a rapid tetramer-dimer interconversion. The addition of pyruvate, the substrate, along with the three cofactors, resulted in a further increase in sedimentation rate, due presumably to an increase in the tetramer-to-dimer ratio. The addition of valine to the complete system resulted in maintenance of the enzyme in the dimeric state concomitant with inhibition of enzyme activity.

Acetolactate Synthase↗
PubMed1976

Immunoadsorbents: non-specific binding of proteins to albumin-sepharose.

Human serum albumin-Sepharose was prepared by coupling human serum albumin to cyanogen bromide activated Sepharose 4B. This immunoadsorbent showed considerable non-specific protein adsorption. The adsorbed proteins were mainly immunoglobulins which could not be separated from required antibody. It is suggested that basic groups formed in the preparation of the albumin-Sepharose are responsible for this non-specific protein adsorption. Non-specific protein adsorption could be completely eliminated by neutralizing the basic groups of the albumin-Sepharose with the anionic dye blue dextran. The resultant blue dextran-albumin-Sepharose allowed purification of anti-albumin-antibody with high yield. It is shown that the isolated antibody is pure and retains its native properties.

Adsorption↗
PubMed1976

Threonine deaminase from a nonsense mutant of Escherichia coli requiring isoleucine or pyridoxine: evidence for half-of-the-sites reactivity.

The mutant IP7 of Escherichia coli B requires isoleucine or pyridoxine for growth as a consequence of a mutation in the gene coding for biosynthetic threonine deaminase. The mutation of IP7 was shown to be of the nonsense type by the following data: (1) reversion to isoleucine prototrophy involves the formation of external suppression at a high frequency, as shown by transduction experiments; and (ii) the isoleucine requirement is suppressed by lysogenization with a phage carrying the amber suppressor su-3. Cell extracts of the mutant strain contain a low activity of threonine deaminase. The possibility that this activity is biodegradative was ruled out by kinetic experiments. The mutant threonine deaminase was purified to homogeneity by conventional procedures. The enzyme is a dimer of identical subunits of an approximate molecular weight of 43,000 (Grimminger and Feldner, 1974), whereas the wild-type enzyme is a tetramer of 50,000-dalton subunits (Calhoun et al., 1973; Grimminger et al., 1973). The mutant enzyme is not inhibited by isoleucine and does not bind isoleucine, as shown by equilibrium dialysis experiments. Pyridoxal phosphate enhances the maximum catalytic activity of the mutant enzyme by a factor of five, whereas the wild-type enzyme is not affected. In wild-type and mutant threonine deaminase the ratio of protein subunits and bound pyridoxal phosphate is 2:1. The activation of threonine deaminase from strain IP7 is due to a second coenzyme binding site, as shown by (i) spectrophotometric titration of the enzyme with pyridoxal phosphate and by (ii) measurement the pyridoxal phosphate content of the enzyme after sodium borohydride reduction of the protein. The observation of one pyridoxal phosphate binding site per peptide dimer in the wild-type enzyme and of two binding sites per dimer in the mutant strongly suggests that one of the potential sites in the wild-type enzyme is masked by allosteric effects. The factors responsible for the half-of-the-sites reactivity of the coenzyme sites appear to be nonoperative in the mutant protein.

Binding Sites↗
PubMed1975

Purification of biosynthetic threonine deaminase from Escherichia coli.

Biosynthetic threonine deaminase (L-threonine hydro-lyase (deaminating), EC 4.2.1.16) was purified to apparent homogeneity from cell extracts of Escherichia coli by chromatographic procedures using valine-Sepharose, isoleucine-N-hexamethyleneamine-Sepharose, and hydroxyapatite with an overall yield of 40%. Analytical ultracentrifugation shows a molecular weight of 214 000. In sodium dodecyl sulfate gel electrophoresis, the enzyme migrates as a single band corresponding to a molecular weight of about 50 000. These data confirm that the enzyme is a tetramer. The sedimentation coefficient, s-020,w, determined by differential sedimentation experiments is 9.2 S. The enzyme shows absorption maxima at 415 and 280 nm. Determination of pyridoxal phosphate by three indenpendent methods shows the presence of two molecules of pyridoxal phosphate per enzyme molecule, the different methods being in excellent agreement equilibrium dialysis experiments establish the presence of two isoleucine binding sites. The Scatchard plot suggests non-cooperativity of these sites. The association constant for isoleucine is 1.2 - 10(5)M-1.

Binding Sites↗
PubMed1972

Isoleucine auxotrophy due to feedback hypersensitivity of biosynthetic threonine deaminase.

Isoleucine-deficient mutants of Salmonella typhimurium were isolated. Three groups of mutants can be discerned by their nutritional requirements and enzyme patterns. (i) Mutants which grow with isoleucine alone are devoid of biosynthetic threonine deaminase (TD). (ii) Mutants growing with isoleucine and valine are devoid of transaminase B. (iii) Mutants growing with either isoleucine or threonine have normal levels of TD. However, the sensitivity of this enzyme to feedback inhibition by isoleucine is greatly enhanced. The inhibitory effect of isoleucine can be counterbalanced by high concentrations of threonine. These results indicate that the production of isoleucine in the mutants is restricted to a low level not sufficient to support the growth of the cells. This hypothesis is confirmed by studies with revertants of an isoleucine-threonine mutant. In nine revertants, wild-type properties of TD have been restored. In four revertants, the hypersensitivity of TD is unchanged, but the strains produce a greatly enhanced quantity of threonine, which is excreted into the culture medium. It follows, that hypersensitivity of TD to inhibition by isoleucine is the cause of the nutritional requirement of isoleucine-threonine mutants.

Cell-Free System↗