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Biomedical subjects

M Gregoriou

Publications and source records attributed to M Gregoriou.

26 records · Page 2Linked to original sources
PubMed1980

Adaptation to phenylacetamide as a growth substrate by an acetanilide-utilizing mutant of Pseudomonas aeruginosa.

Mutants able to utilize phenylacetamide as sole nitrogen source were isolated from the acetanilide (N-phenylacetamide) - utilizing Pseudomonas aeruginosa mutant strain A13 and from its parent strain L 10. Growth properties of the mutants (Ph strains) on amide media and the physicochemical properties of their amidases in cell free extracts indicated that their phenylacetamidase activities were attributable to alterations in their amidases. Differences in amide hydrolase specificities between the AI3- and the L 10-Ph mutants were observed. The AI3 group had a high level of activity towards 4-nitrophenylacetamide, activity towards phenylacetyl-4-nitroaniline but, unlike strain AI3, no activity towards acetyl-4-nitroaniline; the L 10 group had a low activity towards 4-nitrophenylacetamide, no activity towards phenylacetyl-4-nitroaniline but retained the low level of activity towards acetyl-4-nitroaniline exhibited by strain L 10. Confirmation of the association between these altered specificities and alterations in amidases was obtained from analysis of the properties of phenylacetamidases purified from an AI3-Ph mutant (pH 5) and an L 10-Ph mutant (Ph14). The original mutation in the amidase gene of strain AI3 appeared responsible for the differences between the two groups of Ph mutants and the binding interactions with acetanilide that it determined were eliminated in AI3-Ph mutants.

Acetanilides↗
PubMed1979

Inhibition of the aliphatic amidase from Pseudomonas aeruginosa by urea and related compounds.

The time-dependent inhibition of amidase from Pseudomonas aeruginosa strain AI 3 by urea, hydroxyurea and cyanate displayed saturation kinetics fitting a model for the reaction sequence in which formation of a complex in a reversible step was followed by an irreversible step. Altered amidases from mutant strains AIU 1N and OUCH 4, selected for their resistance to inhibition of growth by urea and hydroxyurea respectively, had altered kinetic constants for inhibition indicating reduced binding capacity for the inhibitors. The substrate acetamide protected AI 3 amidase against inhibition by urea,.and altered Ki values for inhibition of the mutant amidases were paralleled by alterations in Km values for acetamide indicating that urea acted at the active site. Inhibition of AI 3 amidase involved the binding of one molecule of urea per molecule of enzyme. Urea inhibited amidase slowly regained activity at pH 7.2 through release of urea.

Amidohydrolases↗
PubMed1979

Mammalian hexokinases: a system for the study of co-operativity in monomeric enzymes.

Kinetic and structural studies have been carried out of two isoenzymes of hexokinase from the rat, hexokinase II and glucokinase. Although both enzymes are monomeric, hexokinase II has a molecular weight double that of glucokinase and resembles a dimer of glucokinase. The co-operativity of glucokinase, which is not observed for hexokinase II, appears to be kinetic in origin rather than the consequence of ineractions between distinct glucose-binding sites.

Animals↗
PubMed1978

Relationship between mutant amidases of Pseudomonas aeruginosa and hydroxyurea as an inhibitor.

Hydroxyurea inhibited growth of Pseudomonas aeruginosa strain AI 3 on media containing either acetanilide (N-phenyl acetamide) or acetamide as sole carbon sources. Mutants resistant to hydroxyurea inhibition of growth on acetanilide (OUCH strains) and acetamide (AmOUCH strains) displayed altered growth properties on various amide media compared with the parent strain AI3. AI3 amidase, which catalyses the initial step in the metabolism of acetanilide and acetamide, was inhibited by hydroxyurea in a time-dependent reaction that was slowly reversible at pH 7.2. Compared with AI3 amidase, amidases from the OUCH mutants were much less sensitive to inhibition by hydroxyurea and showed altered substrate specificities and pH/activity profiles; amidases from the AmOUCH mutants were more sensitive to hydroxyurea inhibition but showed increased activity towards acetamide. Association of resistance to hydroxyurea inhibition with a mutation in the amidase structural gene of strain OUCH 4 was confirmed by transduction.

Amidohydrolases↗
PubMed1977

Pseudomonas aeruginosa mutants resistant to urea inhibition of growth on acetanilide.

Pseudomonas aeruginosa AI 3 was able to grow in medium containing acetanilide (N-phenylacetamide) as a carbon source when NH4+ was the nitrogen source but not when urea was the nitrogen source. AIU mutants isolated from strain AI 3 grew on either medium. Urease levels in bacteria grown in the presence of urea were 10-fold lower when NH4+ or acetanilide was also in the medium, but there were no apparent differences in urease or its synthesis between strain AI 3 and mutant AIU 1N. The first metabolic step in the acetanilide utlization is catalyzed by an amidase. Amidases in several AIU strains showed altered physiochemical properties. Urea inhibited amidase in a time-dependent reaction, but the rates of the inhibitory reaction with amidases from the AIU mutants were slower than with AI 3 amidase. The purified amidase from AIU 1N showed a marked difference in its pH/activity profile from that obtained with purified AI 3 amidase. These observations indicate that the ability of strain AIU 1N and the other mutants to grow on acetanilide/urea medium is associated with a mutation in the amidase structural gene; this was confirmed for strain AIU 1N by transduction.

Acetanilides↗
PubMedDate not supplied

p53 protein expression in breast carcinomas. Comparative study with the wild type p53 induced proteins mdm2 and p21/waf1.

The aim was to investigate the pattern of expression of p53 protein and two wild-type (wt) p53-induced proteins (mdm2 and p21/waf1), as an indirect way of assessing p53 gene status in breast carcinomas. Formalin-fixed paraffin embedded tissue from 102 cases of breast carcinomas comprising mostly ductal carcinomas (88 cases) was stained by immunohistochemistry for p53, mdm2 and p21/waf1 proteins. We found p53, mdm2 and waf1/p21 protein expression in 33/102, 20/102 and 38/102 breast carcinomas, respectively. Parallel p53/mdm2 protein expression was found in 9 cases. Five were also p21/waf1 positive. Discordant p53+/ mdm2-protein expression was found in 24 cases. Nine were p21/waf1 positive and the remaining fifteen were p21/waf1 negative. The patterns mdm2+/p53-/p21- and p21+/p53-(+)/mdm2- were found in 6 and 20 cases, respectively. Parallel p53/mdm2/p21 protein expression may represent breast carcinomas with wt p53 gene since mdm2 and p21 proteins are inducible by wt p53 gene. In these cases p53 protein expression may be due to stabilisation to mdm2 protein. This could be important in the pathogenesis of these cases since mdm2 may deregulate the p53-dependent growth suppressive pathway. Discordant p53+/mdm2-/p21- protein expression may represent breast carcinomas with p53 gene mutations unable to activate expression of mdm2 and p21 proteins. Breast carcinomas with p53+/mdm2/p21+ protein expression may have either wt p53 with deregulated mdm2 gene expression or mutated p53 gene with p53-independent p21 expression. Cases with only mdm2 expression may represent tumours with mdm2 gene amplification or overexpression and cases with only p21 expression may reflect p53-independent regulation of p21 protein.

Breast Neoplasms↗