Tear film MMP accumulation and corneal disease

BACKGROUND/AIMS

Matrix metalloproteinases (MMPs) accumulate in the tears of patients with active peripheral ulcerative keratitis (PUK) but it is unknown whether these enzymes have a central role in disease progression. The aims of the present investigation were to determine the source of these enzymes and to ascertain whether their accumulation in tears is a phenomenon specific to PUK or a general feature of other anterior segment diseases.

METHODS

The experimental samples were obtained from the culture media of conjunctival and corneal epithelial cells, from fractionated blood plasma and leucocytes of healthy subjects and patients with rheumatoid arthritis, and from the tears of healthy subjects and patients with a variety of anterior segment diseases. The MMPs of all samples were visualised by zymography and tear samples were assayed using nitrophenol acetate and an MMP-9 susceptible quenched fluorescent peptide as substrate.

RESULTS

The major MMPs that accumulate in the tears of patients with rheumatoid arthritis with active ocular disease are MMP-9 and a species of M(r) 116,000. By comparing the zymographic activity profiles of the gelatinases present in the samples obtained, it was deduced that the main source of these MMPs was granulocytes. Their accumulation in tears was not unique to patients with PUK; detectable amounts of the enzymes also occurred in the tears of patients with keratoconus with associated atopic disease, patients undergoing treatment for herpetic eye disease, and patients with systemic and non-systemic dry eye disease.

CONCLUSION

The MMPs that accumulate in tears are mainly derived from granulocytes. This may be effected by autoimmune diseases that involve ocular tissue or by ocular diseases that induce an inflammatory response.

Matrix metalloproteinase 2 activation in cultured corneas

PURPOSE

Corneas that are maintained in tissue culture medium shed their epithelial cells and repopulation following graft surgery is an essential facet of the healing process. Failure to do so may be a result of structural damage to the epithelial basement membrane of a donor cornea. The purpose of the present investigation was to ascertain whether MMP-2, the matrix metalloproteinase produced by corneal keratocytes, may be activated during storage and hence cleave the type IV collagen component of the epithelial cell basement membrane.

METHODS

Fresh and transplant rejected corneas that had been stored in culture medium for varying time periods and of known donor age were collected. The soluble protein fractions of these corneas were obtained. Their MMP-2 proteins were visualised by zymography on SDS gelatin polyacrylamide gels and assayed for activity against nitrophenyl acetate and denatured [(3)H]type I collagen.

RESULTS

The stromal tissue of fresh, normal corneas produced inactive MMP-2 of M(r) 66,000. Although the cultured corneas did not up-regulate MMP-2 production, they contained additional MMP-2 activities of M(r) 62,000 and M(r) 43,000. The appearance of these additional MMP-2 activities correlated with corneal culture time but not donor age. The ability to cleave denatured [(3)H]type I collagen correlated with the appearance of the M(r) 43,000 activity but not the M(r) 62,000 activity.

CONCLUSION

Activated MMP-2 is produced in cultured corneas. For this reason the corneas donated for all graft procedures should not be held in culture medium for periods exceeding 4 weeks.

A role of her own: female cowbirds, Molothrus ater, influence the development and outcome of song learning

Previous work has shown that captive female cowbirds, Molothrus ater, can influence the outcome of male song development by affecting retention or deletion of song elements and by stimulating improvization. Here we looked for evidence of female influence during the process of learning, as males progress from subsong to plastic song to stereotyped song. In a longitudinal study, we measured the rate and timing of vocal development in captive, juvenile male brown-headed cowbirds, M. a. artemisiae. Half the young males were housed with female cowbirds from their own population (South Dakota: SD) and half with female cowbirds from a M. a. ater population (Indiana: IN). Both populations of females prefer local songs and differ in the time of breeding, with SD females breeding 2 weeks later than IN females. The results showed significant effects of female presence on the age at which males advanced through stages of vocal development: the SD males with SD females, as opposed to SD males with IN females, developed stereotyped song earlier, reduced motor practise earlier, and produced more effective playback songs. Longitudinal observations of social interactions showed that the two groups of females reliably differed in social responses to males. Degree of social proximity of females to males in the winter predicted song maturity, rate of rehearsal and song potency. Thus, females can stimulate the progression of song learning, as well as prune song content. Copyright 2000 The Association for the Study of Animal Behaviour.

The control of matrix metalloproteinase-2 expression in normal and keratoconic corneal keratocyte cultures

PURPOSE

Early phase keratoconic corneas and their cultured keratocytes abnormally produce the Mr 62,000 form of the matrix metalloproteinase-2 (MMP-2). It is known that platelet derived growth factor (PDGF) and transforming growth factor-beta (TGF-beta) are involved in the regulation of MMP activity and tissue inhibitor of metalloproteinase (TIMP) production in non-ocular tissues. The purpose of this enquiry was to determine whether these growth factors also play a role in the activity and/or production of corneal MMP-2 and TIMP, and whether their activity could account for the existence of the Mr 62,000 form of MMP-2 in keratoconic corneas.

METHODS

Confluent cultures of normal and early-phase keratoconic corneal keratocytes were established and incubated in serum-free media in the presence or absence of PDGF and TGF-beta. The proteins secreted by these cells over periods of 7 days were harvested for analysis. The total protein produced was determined spectrophotometrically. MMP-2 was visualised by SDS-gelatin polyacrylamide gel electrophoresis and assayed using radiolabelled type IV collagen as substrate. The enzyme inhibitors, TIMP-1 and TIMP-2, were quantified by dot blot immunoassay.

RESULTS

The addition of PDGF or TGF-beta to the culture medium of keratoconic corneal keratocytes had no significant effect on overall protein production, MMP-2 activity or on the amounts of TIMP- 1 and TIMP-2 secreted. These observations also applied to normal corneal keratocytes, with the exception that PDGF induced expression of the Mr 62,000 species of MMP-2.

CONCLUSIONS

PDGF may be involved in the production of the Mr 62,000 species of MMP-2 that is abnormally produced by early-phase keratoconic corneal keratocytes.

Matrix metalloproteinase 2: involvement in keratoconus

PURPOSE

The activation of matrix metalloproteinase-2 (MMP-2) is postulated to be a crucial pathogenic factor behind progressive and chronic diseases in which basement membranes are disrupted. An ocular example is keratoconus. The purpose of the present enquiry was therefore to investigate and compare the activities of the MMP-2 secreted by keratocytes of normal and keratoconic corneas.

METHODS

The spectrum of MMP-2 activities secreted by cultures of keratocytes derived from normal and keratoconic corneas was analysed by zymography. Subsequently, selected preparations were assayed for peptidase activity, using Type I, Type III, Type IV and Type V collagen as substrate, under native conditions and after treatment with a variety of putative activating reagents.

RESULTS

Although MMP-2 of Mr 65,000 on SDS gelatin polyacrylamide gels is the major protease secreted by keratocytes of normal corneas, the keratocytes of early-phase keratoconic corneas secrete an additional zymographic activity of Mr 61,000. From their N-terminal amino acid sequences, both these proteins were shown to be conformers of proMMP-2. Treatment with SDS followed by protein fractionation was required to achieve in vitro activation of the MMP-2 secreted by normal corneal keratocytes. Treatment with SDS alone partially activated the enzyme produced by early-phase keratoconic corneal keratocytes. This procedure and autocatalysis, yielded an enzyme of Mr 43,000 that selectively hydrolysed Type IV and denatured Type 1 collagen.

CONCLUSIONS

The zymographic gelatinase activities of apparent Mr 65,000 and 61,000 are conformers of corneal proMMP-2. Activated enzyme, of Mr 43,000, is more readily generated from protein preparations of the culture media of early phase keratoconic corneal keratocytes than from protein preparations of the culture media of normal corneal keratocytes.

Role of ocular matrix metalloproteinases in peripheral ulcerative keratitis

AIM

Peripheral ulcerative keratitis (PUK) is an ocular manifestation of rheumatoid arthritis and other similar systemic diseases. The purpose of this inquiry was to investigate the involvement of matrix metalloproteinases (MMPs) in the induction and/or maintenance of PUK.

METHODS

Substrate gel electrophoresis was used to characterise the MMP activities secreted by primary cultures of keratocytes derived from normal and perforated pathological corneal specimens, and those present in tears of normal subjects and patients with PUK. Substrate specificity and the in vivo activity status of the secreted MMPs was assessed by SDS-polyacrylamide gel electrophoresis of standard collagens incubated in the presence or absence of the various enzyme preparations.

RESULTS

In addition to MMP-2 of M(r) 66,000, cultured keratocytes derived from perforated corneas of patients with PUK abnormally produce the MMP-2 of apparent M(r) 62,000. Other MMPs and in particular MMP-9 of M(r) 92,000, also occur in the tears of these patients. Their visualisation on substrate polyacrylamide gels correlated with clinical manifestations of disease activity; during periods of disease quiescence they were barely detectable. The steroid prednisolone, frequently used in systemic therapy, had no effect on the in vitro activity of MMP-2, or on its production by cultured corneal keratocytes. Although the in vitro activity of MMP-2 was inhibited by both Cu(2+) and Zn(2+), Cu(2+) apparently induced the keratocytes to produce activated enzyme and Zn(2+) irreversibly inhibited their production of MMP-2.

CONCLUSION

Overexpression of corneal MMP-2 and tear film MMP-9 are characteristic features of patients with PUK and their activation may be a crucial facet of disease initiation or progression. Although effective in systemic therapy for PUK, prednisolone had no direct control over corneal MMP-2 production or activity. Zn(2+) on the other hand inhibited both MMP-2 production and MMP-2 activity and may, therefore, be of therapeutic value if suitably formulated and used in conjunction with systemic steroid treatment.

Nonunion of the distal radius

We report five cases of nonunion of the distal radius. There were three women and two men. The mean age was 44 years (range, 34-56). All five patients were heavy tobacco smokers and three had a history of alcohol abuse. In three patients, union of the distal radius was obtained. Two had a persistent nonunion which was salvaged with a total wrist fusion.

Localisation of connective tissue and inhibition of autofluorescence in the human optic nerve and nerve head using a modified picrosirius red technique and confocal microscopy

The use of picrosirius red to localise connective tissue in thin tissue sections viewed by bright-field microscopy is well documented. Its use on thin tissue sections imaged by fluorescence confocal microscopy has also been reported. Here we describe modifications to published procedures that allow picrosirius red staining of thick 60-microm sections and their subsequent analysis by confocal microscopy. The use of phosphomolybdic acid pre-treatment was found to be essential for confocal analysis; in addition to preventing non-specific staining, it also quenched tissue autofluorescence. By incubating sections free-floating, pre-treating them with phosphomolybdic acid for 30 min and imaging them using an argon ion laser we were able to use confocal microscopy to image the entire depth of 60-microm human optic nerve and nerve head sections stained with picrosirius red. The application of this modified picrosirius red and confocal microscopy technique should be useful for analysing the three-dimensional structure of the optic nerve and other tissues with a similarly complex arrangement of connective tissue.

Over-expression of a gelatinase A activity in keratoconus

Keratoconus is an ocular disorder in which the central cornea becomes thin, conical and frequently scarred. We are exploring the possibility that this condition is induced and maintained by proteases that exist in the corneal matrix in an activated form. In this study, the activities of the proteases secreted in vitro and in vivo by keratocytes of normal, clear keratoconic, scarred keratoconic and traumatically scarred corneas have been compared and partially characterised. Data obtained by assaying acyl transferase activity showed that the matrix metalloproteinases account for a minimum of 95% of the total protease secreted by cultured keratocytes. Their summated specific activity was consistently and significantly higher in the culture medium of keratoconic keratocytes than in the medium of other keratocyte cultures. Analysis of the individual protease activities secreted by these corneal keratocytes in vitro and in vivo by SDS-gelatin polyacrylamide gel electrophoresis showed that a gelatinase of molecular weight 65,000 is the major protease secreted by normal keratocytes. Whereas clear keratoconic and traumatically scarred corneal keratocytes secrete an additional activity of molecular weight 61,000, scarred keratoconic corneal keratocytes generally produced little or none of this gelatinase activity. Both activities may be ascribed to gelatinase A, and although the 61,000 molecular weight form may be a significant feature of keratoconus, neither appears to be active as secreted.

The Distribution of Gibberellins in Vegetative Tissues of Pisum sativum L. : I. Biological and Biochemical Consequences of the le Mutation

The concentrations of endogenous gibberellin (GA) 1, 5, 8, 19, 20, and 29 in the component tissues of maturing tall (Le) and dwarf (le) pea (Pisum sativum) plants have been determined. The following conclusions were drawn from the data obtained: (a) GA(20) and its metabolites accumulate only in the growing regions of Le and le plants; (b) the le mutation is biochemically expressed in all immature tissues of the dwarf plants; (c) the quantitative composition of the GA metabolites in the various immature tissues is variable; (d) the total GA concentration in apical buds, unexpanded leaves, and tendrils is considerably higher than in GA(1)-responsive stem tissue; and (e) there is very little GA accumulation of the inactive 2beta-hydroxylated GAs (GA(8) and GA(29)) in either the mature vegetative tissues or the roots of pea plants.

Gibberellin A(1) Biosynthesis in Pisum sativum L. : II. Biological and Biochemical Consequences of the le Mutation

A comparative study of the metabolism of radiolabeled gibberellin (GA) 1, 19, and 20 in isolated vegetative tissues of isogenic Le and le pea (Pisum sativum) plants incubated in vitro with the appropriate GA substrate is described. The results of this study provide evidence that the enzymes involved in the latter stages of GA biosynthesis are spatially separated within the growing pea plant. Apical buds were not apparently involved in the production of bioactive GA(1) or its immediate precursors. The primary site of synthesis of GA(20) from GA(19) was immature leaflets and tendrils, and the synthesis of bioactive GA(1) and its inactive catabolite GA(8) occurred predominantly in stem tissue. GA(29), the inactive catabolite of GA(20), was produced to varying extents in all the tissues examined. Little or no difference was observed in the ability of corresponding Le and le tissues to metabolize radiolabeled GA(1), GA(19), or even GA(20). During a fixed period of 24 hours, stems of plants carrying the le mutation produced slightly more [(3)H]GA(1) (and [(3)H]GA(29)) than those of Le plants. It has been concluded that the le mutation does not lie within the gene encoding the GA(20) 3beta-hydroxylase protein.

Selecting a healthcare consultant, Part II: Developing the request for proposal

In part II of this series, Janet Scheuerman of Herman Smith Associates and Vaughan A. Smith, president of the American Association of Healthcare Consultants, continue their detailed analysis of how to select a healthcare consultant. Focusing on the request for proposal (RFP), the authors cover such practical considerations as how many copies of the RFP will be required and what contacts should be listed. A comprehensive outline of how to write a statement of purpose and describe the project and scope of work is presented. The article concludes with suggestions for interviewing candidates and checking references.

Selecting a healthcare consultant, Part I: How to get started

Janet L. Scheuerman and Vaughan A. Smith outline the factors that determine why and when consulting services are appropriate, presenting an overview of the initial steps in consultant selection. The expertise of a consultant is often needed for specialized problems, problems needing immediate assessment, drastic rescue situations, difficulties that defy standard solutions, and changes in the regulatory and competitive environment. Many organizational and planning issues also require outside consulting expertise. Institutions use consultants for specialized information, an independent perspective, as catalysts for change, and for cost-effective service and education. The consulting process consists of five phases; Part I provides a careful analysis of crucial preliminary selection activities. An organizational commitment to the process must be made, and needs, key issues, and expectations defined before selecting a committee and identifying potential consulting sources. Part II will appear in the next issue of the JQA.

Immunochromatographic purification of gibberellins from vegetative tissues of Cucumis sativus L: Separation and identification of 13-hydroxy and 13-deoxy gibberellins

Immunological methods are described for the separation and purification of 13-hydroxy and 13-deoxy-gibberellins of Cucumis sativus. Qualitative and quantitative data show that 13-deoxygibberellins predominate over 13-hydroxygibberellins in stems and leaves of this species.

The endogenous gibberellins of dwarf mutants of lettuce

The gibberellin (GA) content of E-1, a tall genotype of early flowering lettuce (Lactuca sativa L.), and of three selected GA-responsive dwarfs, dwf1, dwf2, and dwf2(1), has been determined using (13)C-labeled internal standards and gas chromatographymass spectrometry (GC-MS). In the shoots of the E-1 parent, GA(1), 3-epi-GA(1), GA(3), GA(5), GA(8), GA(19), GA(20), GA(29), and GA(53) were identified by full scan GC-MS and Kovats retention indices. Purification by immunoaffinity chromatography selective for 13-hydroxy GAs, was necessary for GA identification. Relative to the parent E-1, the concentrations of GA(1), GA(8), GA(20), and GA(29) in the shoots of dwf2 plants were reduced to about 10% and in shoots of dwf2(1) plants to less than 50%. In dwf1 the levels of GA(1), GA(8), and GA(29) were also reduced to less than 50% of the parent E-1, but the level of GA(20) was fivefold higher than in E-1. Plant height was correlated with the endogenous levels of GA(1) and GA(8).

Partial Purification and Characterization of the Gibberellin A(20) 3beta-Hydroxylase from Seeds of Phaseolus vulgaris

The GA(20) 3beta-hydroxylase present in immature seeds of Phaseolus vulgaris has been partially purified and characterized. The physical characteristics of the enzyme are similar to those of the GA 2beta-hydroxylases present in mature and immature seeds of Pisum sativum. It is acid-labile, hydrophobic, and of M(r) 45,000. The enzyme catalyzes the synthesis of GA(1), GA(5), and GA(29) from GA(20). Activity is dependent upon the presence of Fe(2+), ascorbate, 2-oxoglutarate, and oxygen. 2-Oxoglutarate does not function as a cosubstrate; in the presence of the enzyme, succinate is not a reaction product.

Nursing student attrition and implications for pre-admission advisement

The current shortage of nurses and the decreasing student applicant pool supports the need for institutions of higher education to examine the problem of nursing student attrition and possible solutions. This study surveyed 227 non-returning students to identify attrition factors. The results implicate problems with class scheduling, inadequate financial resources, and employment responsibilities. Twenty four nursing faculty members were additionally surveyed to identify factors. The faculty respondents target poor study skills as the primary problem, a finding not agreed on by the former students. These identified problem areas implicate inadequate preadmission advisement. Students should be made aware of the personal and financial costs of a nursing education prior to admission. Preadmission advising that provides an applicant with a more complete understanding of the nursing educational process may help prevent student attrition and the loss of new nurses to the profession.

An immunological approach to gibberellin purification and quantification

Gibberellin (GA) specific, high-affinity monoclonal antibodies have been used to assay the GA content of various plant tissues and to purify selected GAs by immunoaffinity chromatography. These immunological techniques may not stand alone as a general method of GA analysis. The results of this study indicate, however, that in conjunction with gas chromatography-mass spectrometry for positive GA identification, radioimmunoassay and immunoaffinity chromatography are extremely powerful tools for purifying and quantifying GAs from plant tissues.

Enzymes from seeds of Phaseolus vulgaris L.: Hydroxylation of gibberellins A20 and A 1 and 2,3-dehydrogenation of gibberellin A 20

A time-course study is described relating the enzyme activities for GA20 metabolism with seed development in Phaseolus vulgaris L. Enzyme activity for the 3β-hydroxylation of GA20 to GA1, and for the 2,3-desaturation of GA20 to GA5, was confined to the cotyledons and showed maximal specific activity at 21 d after anthesis. These enzyme activities co-occurred, together with a much lower level of activity for the 2β-hydroxylation of GA20 to GA29. The observed rates of GA1, GA5 and GA29 formation from GA20 were constant under a range of incubation conditions. Enzyme activity for the conversion of GA1 to GA8 was detected only in embryos of seed from 40 d after anthesis. By deuterium-labelling and analysis of the products by gas chromatography-selected ion monitoring it was shown that 2β-hydroxylation of GA1 to GA8 and 3β-hydroxylation of GA20 to GA1 occur with retention of configuration and that the conversion of GA20 to GA5 occurs with loss of the 2β- and 3β-hydrogens. These results establish that GA1 is not formed from GA20 via GA5.

The partial purification and characterisation of gibberellin 2β-hydroxylases from seeds of Pisum sativum

The gibberellin (GA) 2β-hydroxylases in mature and immature seeds of Pisum sativum have been partially purified and characterised. The enzymes are unstable when stored below pH 7.0 or in the absence of a thiol reagent. The optimum assay pH is between 7.4 and 7.8 and activity is dependent upon the presence of α-ketoglutarate, Fe(2+) and ascorbate. The 2β-hydroxylase activities for GA1, GA4, GA9 and GA20 are chromatographically inseparable and correspond to a protein of Mr 44000. The rate of GA 2β-hydroxylation varies according to substrate and some evidence indicates that the 2β-hydroxylase activities for GA1 and GA4 and for GA9 and GA20 may reside in different proteins. During pea seed maturation, the specific activity of the enzyme(s) increases dramatically and reaches a maximum at a time when endogenous GA9, GA20, GA29 and GA51 are also at their greatest concentration. This correlation is not the result of substrate induction of enzyme activity. Since the GA 2β-hydroxylases operate at maximal rate at low substrate concentrations they are incapable of rapidly 2β-hydroxylating excessive quantities of (exogenously applied) GA1 or GA20. On the basis of the kinetic parameters of the GA 2β-hydroxylase activities, a generalised model is discussed for the control of the steady-state levels of bioactive hormone under normal physiological conditions.

Pain relief after episiotomy--a comparative study of suprofen and dihydrocodeine

In a single-dose, randomized, double-blind study of 100 women, suprofen and dihydrocodeine were compared in the relief of pain after episiotomy. The drugs were equal in terms of analgesic efficacy, duration of analgesia and onset of action. Neither drug demonstrated any serious adverse effects.

Additional effects of monovalent cations on the lysine-sensitive aspartokinase of E. coli B

The apparent specificity of activation of lysine-sensitive aspartokinase (E.C.2.7.2.4) from E. coli by monovalent cations differs depending on the assay used and on the Mg2+ concentration. Activity is nearly absolutely dependent on and is highly specific for a monovalent cation in the aspartate semialdehyde dehydrogenase coupled assay or the adenosine triphosphate-adenosine diphosphate exchange assay. Little specificity for monovalent cations is observed using the aspartyl hydroxamate assay. Activation and specificity are also altered by Mg2+ concentrations at a constant 5 mM nucleotide concentration. At a low (1.25 or 1.6 mM)Mg2+ concentration, monovalent cation activation and specificity are nearly absolute. Less dependence on monovalent cations and less specificity are observed at a higher Mg2+ concentration (6 mM). Li+ inhibits aspartokinase competitively with respect to either K+ or NH4+. Monovalent cations are also thermoprotective and differential thermal inactivation experiments at 56 degrees C reveal that NH4+ and K+, either of which will produce maximum catalytic activity, interact differently with aspartokinase. K+ interacts with positive cooperativity, whereas NH4+ does not. K+, NH4+, and Na+ are about equally effective in enhancing the dissociation of the aspartokinase-aspartylphosphate complex. Li+ is less effective.

Passage of bacterial DNA into host cells during in vitro transformation of Nicotiana tabacum by Agrobacterium tumefaciens

Tumorigenic and non-tumorigenic strains of Agrobacterium tumefaciens were labelled with tritiated thymidine and added separately to suspension cultures of X-D line habituated tobacco cells. The subsequent association of bacteria with plant host cells and the passage of bacteria and bacterial DNA into these cells was examined by conventional light and electron microscopy and light microscope autoradiography. The results suggest that both strains of bacterium enter damaged host cells (via wall lesions), where they remain restricted to cell vacuoles. By 48 h, the radioactive label has spread from the vacuoles of infiltrated cells to the non-vacuolar cytoplasm of the whole callus tissue. Tumorigenic bacteria differ from the non-tumorigenic strain in promoting a significant increase in host cell nuclear volume, which is paralleled by clear and specific nuclear labelling. It is proposed that tumorigenic DNA, but not non-tumorigenic DNA, is specifically incorporated into, and activates, the host cell nucleus.

Regulatory properties of lysine-sensitive aspartokinase under equilibrium conditions

The regulatory properties of the lysine-sensitive aspartokinase (ATP : L-aspartate 4-phosphotransferase, EC 2.7.2.4) have been studied under equilibrium conditions by determining the effects of modifiers on the rate of equilibrium isotope exchange between ADP and ATP. The extent of inhibition by lysine, leucine or phenylalanine is almost independent of substrate concentration but is influenced by the substrate/product ratio. Inhibition by a given concentration of inhibitor is increased when the ADP/ATP ratio is increased indicating a regulatory interaction between end products and cellular energy metabolism. Lysine inhibition is cooperative under equilibrium conditions and the parameters of the Hill equation are nearly identical to those obtained in initial velocity studies. A cooperative heterotropic interaction between lysine and leucine is also observed by the ATP-ADP exchange assay just as it is in initial velocity assays. Thus, the regulatory features of aspartokinase that are observed in initial velocity studies are also manifest under equilibrium conditions as revealed by equilibrium isotope exchange rates.

Amino acid starvation affects the initiation frequency of nucleolar RNA polymerase

The synthesis of ribosomal precursor RNA in mouse ascites nucleoli derived from cells starved for amino acids is compared with the activity of nucleoli from control cells cultivated in the presence of all amino acids. It is shown that deprivation of a single essential amino acid from the culture medium results in a drastic decrease of the RNA-forming capacity of the isolated nucleoli by a factor of 2-3. This switchoff in rRNA synthesis is a very fast process. Half-maximal inactivation occurs after only 30 min. Addition of amino acids to starved cells leads to a rapid recovery, which is reflected by a sharp increase in the RNA polymerase activity of the isolated nucleoli. Studies on the molecular mechanism of this amino acid-mediated control of rRNA synthesis indicate that this effect is not caused by different growth rates of the RNA chains, but rather by an altered initiation frequency of the RNA polymerase in vivo. Whereas in nucleoli derived from cells grown in full medium almost all the polymerase is tightly bound in a transcriptional complex, a high amount of "free" polymerase which becomes active after addition of exogenous template is present in nucleoli from starved cells.

Psychiatric emergencies in family medicine

The family physician is often called upon to deal with psychiatric emergencies. In order to deal with these situations expertly, he/she must be familiar with the techniques of psychiatric assessment and management. A knowledge of community resources is invaluable in treating such patients.