[Must the recurrent nerve in thyroid gland resection always be exposed? A prospective randomized study]

It was the purpose of this study to establish whether it is necessary to identify the recurrent laryngeal nerve intraoperatively when resecting the endemic nodular goiter. We prospectively formed two groups from 800 subtotal unilateral resections ("nerves at risk"). In group I (382 subtotal resections, 48.4%) the nerve was not identified intraoperatively. In group II (413 subtotal resections, 51.6%) the recurrent laryngeal nerve was routinely identified in all cases. The operative technique was standardized, giving special attention to the "anterior lamella". For all patients, preoperative and postoperative evaluation of the vocal cords was performed routinely. Altogether we saw 4 (0.5%) transient vocal cord palsies: 2 in group I and 2 in group II. All 4 laryngeal nerve palsies recovered within 4 months. These data demonstrated that no benefit is gained from routine dissection of the laryngeal nerve during resection of endemic nodular goiter. Therefore the demand for obligatory intraoperative identification of the recurrent nerve is not tenable.

Evidence for the presence of receptors for pituitary adenylate cyclase-activating polypeptide in the neurohypophysis that are positively coupled to cyclic AMP formation and neurohypophyseal hormone secretion

This study examines the neural lobe of the pituitary gland for the presence of receptors for pituitary adenylate cyclase-activating polypeptide (PACAP) and their possible involvement in the regulation of neurosecretion. The presence of PACAP receptors of type I was revealed in the neural lobe, as well as in anterior and intermediate lobes, by means of RT-PCR amplification using selective oligonucleotide pairs of primers. They appeared to be expressed in the tissues as a short form together with an isoform of heavier molecular weight. Activation of receptors in the presence of PACAP stimulated both formation of cyclic AMP (cAMP) and secretion of arginine vasopressin (AVP) in neural lobes, in a dose-related fashion, with half-maximum (EC50) values of 1.0 +/- 0.2 x 10(-9) M and 1.4 +/- 0.3 x 10(-8) M, respectively. Parallel with AVP, PACAP also stimulated oxytocin (OXT) output, with an EC50 value of 0.6 +/- 0.1 x 10(-8) M. In an attempt to localize receptors on cells (mainly astrocyte-like glials or pituicytes) and/or on nerve fibers of the gland, we used cultures of neural lobe cells and explants (in which nerve fibers undergo degeneration), as well as isolated nerve endings. In both cells and nerve terminals, PACAP enhanced accumulation of cAMP, while it triggered AVP secretion from the latter. The stimulatory effect of PACAP on both AVP and OXT release was mimicked by dbcAMP and blocked by H89, an inhibitor of cAMP-dependent protein kinase. We conclude that in the neural lobe, PACAP receptors are localized on both nerve terminals and pituicytes, which participate in the modulation of secretion of neurohypophyseal hormones in an interactive way and mainly through the cAMP signalling route.

Analysis of bcl-2+ lymphocyte subpopulations in inflammatory synovial infiltrates by a double-immunostaining technique

We used a double-immunostaining technique to analyze the distribution of bcl-2+ B and T lymphocytes within the synovial membranes (SM) of 13 patients with rheumatic diseases: 11 with rheumatoid arthritis (RA), 1 with ankylosing spondylitis (AS), and 1 with osteoarthritis (OA). A high proportion (up to 50%) of the lymphocytes belonged to the B cell subset. Most of both T and B lymphocytes were positive for the bcl-2 protein. In germinal centers B lymphocytes were also negative for bcl-2 protein expression, comparable to the situation in germinal centers of secondary lymphatic organs. We conclude that bcl-2- B lymphocytes are submitted to antigen selection in the inflamed SMs while bcl-2 protein expression provides survival signals for their persistence in the infiltrates. The expression of bcl-2 may be an important factor in protecting lymphocytes in SM from apoptosis by glucocorticoids, cytostatic drugs, and irradiation.

Moexipril as add-on therapy to hydrochlorothiazide in moderate to severe hypertension

This double-blind study was conducted to investigate the efficacy, safety and tolerability of three dose levels of moexipril in comparison to placebo as add-on therapy to hydrochlorothiazide (HCTZ) in patients with moderate to severe hypertension. Two hundred patients who did not respond adequately to a 4-week monotherapy with HCTZ-sitting diastolic blood pressure between 95 and 114 mm Hg- entered the 8-week double-blind period. Patients were randomized to once daily placebo or moexipril 3.75, 7.5 or 15 mg as add-on therapy to open-label HCTZ 25 mg. At biweekly visits, blood pressure and heart rate measurements were obtained and the occurrence of adverse experiences was documented. At the 8-week endpoint, adjusted mean reductions from baseline were significantly (p = 0.003) greater in patients receiving moexipril 3.75, 7.5 and 15 mg compared to placebo (-8.4, -8.8 and -8.9 vs. -4.6 mm Hg). No significant differences between the three dose levels of moexipril could be observed. Moexipril was generally well tolerated. The most frequently reported adverse events for moexipril and placebo were headache, flu syndrome and dizziness (6, 7, 5 vs. 4, 0, 4%). The results indicate that the combination of moexipril and HCTZ is a clinically valuable combination in the treatment of patients with moderate to severe hypertension.

Glucose monitoring as a guide to diabetes management. Critical subject review

PURPOSE

To encourage a balanced approach to blood glucose monitoring in diabetes by a critical review of the history, power and cost of glucose testing.

DATA SOURCES

The Cambridge Data Base was searched and was supplemented by a random review of other relevant sources, including textbooks, company pamphlets, and laboratory manuals.

STUDY SELECTION

Keywords used were "glucosuria diagnosis," "blood glucose self-monitoring," "glycosylated hemoglobin," and "fructosamine" for the 10-year period ending 1992, restricted to English language and human.

DATA EXTRACTION

About 200 titles were retrieved and reviewed according to the author's judgment of relevance.

FINDINGS

"Snapshot tests" (venous and capillary blood glucose) and "memory tests" (urine glucose, glycated hemoglobin fractions and fructosamine) must be employed according to individual patients treatment goals. Day-to-day metabolic guidance is facilitated by capillary blood glucose testing for patients receiving insulin and by urine glucose testing for others. Capillary blood glucose testing is mandatory in cases of hypoglycemia unawareness (inability to sense hypoglycemia because of neuropathy) but is not a substitute for a knowledge of clinical hypoglycemia self-care. Criteria by reason (clinical judgement and cost effectiveness) must be separated from criteria by emotion (preoccupation with technology and marketing). No randomized studies show that any of these tests consistently improve clinical outcome. Optimal metabolic control and cost savings can be expected from a rational selection of tests.

Pituitary adenylate cyclase-activating polypeptide induces expression of corticosteroid-binding globulin in cultured fetal hepatocytes: synergy with tri-iodothyronine

The purpose of the present study was to determine whether functional receptors for pituitary adenylate cyclase-activating polypeptide (PACAP) are expressed in cultured rat fetal hepatocytes and eventually play a role in regulating gene expression of corticosteroid-binding globulin (CBG). We found PACAP38 and PACAP27 to elevate cAMP levels in hepatocytes in a dose-dependent manner, with a plateau being achieved at 10 nM and EC50 values of about 0.5-1 nM. PACAP failed to alter the turnover of inositol phosphates, whereas PACAP and VIP stimulated cAMP accumulation in an equipotent manner, suggesting the presence in these cells of type II receptor isoforms. As revealed by measurements of both CBG mRNA levels and concentrations of binding sites, long-term treatment of fetal cells with 10 nM PACAP, although resulting in partial desensitization of peptide-induced cAMP accumulation, caused a significant 3-fold elevation in CBG synthesis. This stimulatory influence of PACAP was mimicked by the cell permeant N6,2'-O-dibutyryladenosine 3',5'-phosphate (dbcAMP). Treatment of hepatocytes with tri-iodothyronine (T3) enhanced CBG expression and, most interestingly, appeared to synergize with PACAP to elicit a 2-3-fold amplification of CBG synthesis. This study thus provides first evidence for the up-regulation by PACAP and cAMP of CBG expression in fetal hepatocytes and for T3's playing a synergistic role in enhancing PACAP-induced synthesis of the binder.

Demonstration of interleukin-1beta and interleukin-6 in cells of synovial fluids by flow cytometry

Cytokine levels are increased in the synovial fluid of affected joints from patients with inflammatory joint diseases. The aim of our study was therefore to determine if and to what extent immmunologically defined subpopulations of mononuclear cells (MNC) in the synovial fluid are responsible for the increased levels of interleukin-1beta (IL-1beta) and interleukin-6 (IL-6) in affected joints. Lipopolysaccharide (LPS) stimulated peripheral MNC were used as positive controls. While soluble IL-1beta (median 167 pg/ml) and IL-6 (median 508 pg/ml) levels were significantly elevated in the synovial fluids tested, IL-1beta and IL-6 were demonstrated by flow cytometry in only a small subpopulation (<=11%) of mononuclear synovial fluid cells in 7/13 patients. Our results suggest that elevated IL-1beta and IL-6 levels in the synovial fluid of inflammatory joints are derived mainly from cells in the synovial membrane and only to a minor extent from cells in the synovial fluid itself.

In vitro testing of artificial heart valves: comparison between Newtonian and non-Newtonian fluids

The in vitro testing of artificial heart valves is often performed with simple fluids like glycerol solutions. Blood, however, is a non-Newtonian fluid with a complex viscoelastic behavior, and different flow fields in comparable geometries may result. Therefore, we used different polymer solutions (Polyacrylamid, Xanthan gum) with blood-like rheological properties as well as various Newtonian fluids (water, glycerol solutions) in our heart valve test device. Hydrodynamic parameters of Björk-Shiley heart valves with a tissue annulus diameter (TAD) of 21-29 mm were investigated under aortic flow conditions. Major results can be summarized as follows. The mean systolic pressure differences depend on the model fluids tested. Closing time and closing volume are not influenced by the rheological behavior of fluids. These parameters depend on TAD and the pressure differences across the valve. In contrast, rheological behavior has a pronounced influence upon leakage flow and leakage volume, respectively. Results show furthermore that the apparent viscosity data as a function of shear rate are not sufficient to characterize the rheological fluid behavior relevant to hydrodynamic parameters of the heart valves investigated. Therefore, similarity in the yield curves of non-Newtonian test fluids mimicing blood is only a pre-requisite for a suitable test fluid. More information about the viscous and elastic component of the fluid viscosity is required, especially in geometries where a complex flow field exists as in the case of leakage flow.

Regulation of corticosteroid-binding globulin synthesis by 1alpha,25-dihyroxy-vitamin D3 (calcitriol), 9-cis-retinoic acid and triiodothyronine in cultured rat fetal hepatocytes

Evidence regarding the nature of the regulatory factors which directly act upon liver cells and extra-hepatic tissues to alter CBG synthesis is scarce. The present study used cultured rat fetal hepatocytes to investigate the involvement and possible interplay in this process of several members of the nuclear receptors superfamily: vitamin D (VDR), retinoic acids (RAR/RXR) and thyroid hormones (TR). Treatment of cells with 1alpha,25-(OH)2D3 (1,25-D) elicited a dose-dependent inhibition of basal CBG concentration in culture medium. Maximum inhibition to about 15% of control level was achieved with 0.1-1.0 nM, with an IC50 of 3.8 x 10(-12) M and with no significant change in binding affinity. Differential activation of RAR and RXR with either 9-cis-retinoic acid (9-cis-RA) or the RAR-selective synthetic retinoid TTNPB revealed that high doses of both drugs diminished CBG expression, though the former proved about 10-times more potent than the latter in this regard. Amplification by triiodothyronine (T3) of CBG synthesis failed to block the inhibitory effects of either 1,25-D or retinoids, as revealed by both binding capacity and mRNA measurements. Relative to CBG, 1,25-D similarly depressed the synthesis of alpha-fetoprotein (AFP), while on the contrary, retinoids and T3 were shown to cause opposite effects, as 9-cis-RA and TTNPB elevated and T3 decreased AFP expression. The present findings identify for the first time ligands of VDR and RAR/RXR as powerful negative regulators of both basal and T3-stimulated CBG biosynthesis in fetal hepatocytes and suggest lack of a functional interplay between TR and VR or RAR/RXR in these processes.

[Prevalence of human herpesvirus 7 in Mexican blood donors]

The human herpes virus 7 (HHV-7) has been recently isolated from CD4 cells of healthy persons. The present study describes the antibody prevalence of this virus in a healthy Mexican population. Two hundred blood samples from candidates for blood donation at the Hospital General de Mexico were studied with the indirect immunofluorescence test (IFA) in HHV-7 infected SupT1 cells. The testing was done in the University of Cologne, Germany; 167 were males and 33 female; the donors came from 12 of the 31 states in the Mexican republican, predominantly from Mexico City (60.5%) and the State of Mexico (28%). Their mean age was 29.2 years. All but three samples were positive to the HHV-7 (98.5% positivity). Nearly 85% had high titers (> or = 1:80). Other serology testing in the samples revealed 1% positive tests to hepatitis B, 2% to syphilis, and 0.5% to brucella. Hepatitis C and the HIV test were negative in all. The high prevalence of HHV-7 in our donor population should be further studied in order to determine titers indicative of an active infection and of their association with illnesses.

The B lymphocyte in rheumatoid arthritis: analysis of rearranged V kappa genes from B cells infiltrating the synovial membrane

The participation of the humoral immune system in rheumatoid arthritis (RA) is characterized by the production of rheumatoid factors (RF). RF are autoantibodies against the Fc part of IgG which are encoded by diverse germ-line genes. Most of the RF-encoding genes are unmutated, but in RA, a substantial quantity is encoded by somatically mutated genes. In addition, the synovial membranes (SM) of the diseased joints of RA patients are infiltrated by B lymphocytes which form germinal center-like aggregates. To analyze the local immune response, B cell foci from two RA SM were isolated by micromanipulation. From DNA of these foci, the rearranged kappa light chain variable region (V kappa) genes were amplified by polymerase chain reaction (PCR), cloned and sequenced. The amplification of different V kappa-J kappa combinations of different foci suggested oligoclonal expansion of B lymphocytes, which was confirmed by sequence analysis: each PCR product contained members of a single B cell clone. The sequence analysis of 29 different clones revealed rearrangements of diverse V kappa genes. Both frequent representatives of the V kappa 3 and the V kappa 1 family, as well as rarely used genes such as the L10 and B2 genes of the V kappa 2 and V kappa 5 families were found. Of the eleven potentially functional gene rearrangements, eight were significantly mutated, indicating their derivation from antigen-selected B cells. Intraclonal diversity in one of these clones may suggest ongoing mutation in the diseased synovial membrane of patients with RA.

Characterisation of the neurosensory elements of the feline cranial cruciate ligament

The identification and distribution of mechanoreceptors in the cranial cruciate ligament of the cat (analogous to the anterior cruciate ligament in other species) was studied histologically using a modified celloidin embedding technique to achieve serial sectioning of bone-ligament-bone preparations with gold chloride staining. We identified distinctive large elongated structures situated between the collagen bundles of the ligament (resembling endings described as Freeman and Wyke type III; also termed Golgi tendon receptors). These endings were found near the middle of the ligament well away from the bone-ligament junction. Axons seen entering only one end of each type III ending helped to confirm its neural basis. While we saw structures resembling types I and II endings (i.e. Ruffini and pacinian endings, respectively) in individual sections, serial sections failed to reveal convincing evidence of their existence. Such structures almost always appeared to be vascular in nature on adjacent sections, with vessels entering and exiting. We conclude that serial sections are critical to interpreting the presence or absence of mechanoreceptors.

Purification and characterization of recombinant cytochrome P450TYR expressed at high levels in Escherichia coli

The multifunctional tyrosine N-hydroxylase, cytochrome P450TYR (CYP79), from Sorghum bicolor catalyzing the conversion of tyrosine to p-hydroxyphenyl-acetaldoxime in the biosynthesis of the cyanogenic glucoside dhurrin, has been expressed in Escherichia coli using the isopropyl-beta-D-thiogalactopyranoside-inducible vector pSP19g10L, containing the cDNA encoding CYP79. The expression construct was optimized by reducing the length of the N-terminal hydrophobic core of the signal sequence of cytochrome P450TYR and by exchanging the first eight codons with the first eight codons of bovine P45017 alpha. The highest yielding construct provided 200-500 nmol P450TYR/liter cell culture. The recombinant P450TYR was gently and efficiently extracted from E. coli spheroblasts by temperature-induced phase partitioning of Triton X-114 in the presence of 30% glycerol and isolated by DEAE and reactive red chromatography. In reconstitution experiments using saturating amounts of sorghum NADPH-cytochrome P450 reductase, the Km and turnover rate for isolated recombinant P450TYR was 0.22 +/- 0.06 mM and 49.2 +/- 3.8 min-1, respectively, whereas a turnover rate as high as 350 min-1, was obtained using E. coli membranes. Addition of 3 mM glutathione stimulated the activity of reconstituted P450TYR and of sorghum microsomes although the effect was highly variable. Phenylalanine, the precursor of several cyanogenic glucosides, gave a type I binding spectrum, but was not metabolized by P450TYR, demonstrating the high substrate specificity of this P450. Administration of radioactively labeled p-hydroxyphenylacetaldoxime to E. coli cells, showed E. coli metabolized p-hydroxyphenylacetaldoxime independent of the expression of P450TYR.

Azure B-eosin APAAP staining: a method for simultaneous hematological and immunological cell analysis

Azure B-eosin APAAP staining allows simultaneous analysis of peripheral blood and bone marrow cells for hematological characteristics and immunological cell marker profiles. A defined sequence of staining procedures maintains characteristic components of the Romanowsky-Giemsa stain whereas cell antigens can be detected immunologically using the alkaline phosphatase-anti-alkaline phosphatase (APAAP) detection system. Antigens are visualized by the staining product of the substrate-naphthol AS GR phosphate and variamine blue salt. The usefulness of the azure B-eosin APAAP method was demonstrated on blood and bone marrow smears of patients with various hematological disorders.

Multifactorial regulation of pituitary adenylate cyclase-activating polypeptide (PACAP)-induced production of cyclic AMP in ATT-20 corticotrophs: major involvement of Rolipram-sensitive and insensitive phosphodiesterases

Cyclic nucleotide phosphodiesterases (PDEs) appear to play a major role in the modulation of cellular accumulations of cAMP/cGMP and hence the magnitude of the cell response to a hormone signal. These enzymes are present in cells as multiple isoforms and lie under control of various protein kinases. Because PACAP, unlike corticotropin-releasing factor (CRF), may stimulate a dual signalling pathway in pituitary cells (activating both adenylyl cyclase and phospholipase C), we used AtT-20 corticotrophs and primary cultures of rat pituitary cells to study the effect and possible differential influence of these peptides on cAMP formation. Time-course analysis indicated that, both in the absence and the presence of Rolipram (a selective type IV PDE inhibitor), PACAP stimulated a rapid and short-lived accumulation of cAMP in tumor corticotrophs, while in the presence of the non-selective inhibitor IBMX, the peptide produced a sustained high plateau level of second messenger (10 times the level generated with Rolipram at 20 min). On the contrary, when exposed to CRF, cAMP production augmented in parallel, irrespective of whether Rolipram or IBMX were present. The differential effects of the PDE inhibitors were seen with PACAP concentrations ranging from 0.1 to 100 nM, and could also be demonstrated in primary cultures of pituitary cells. Co-incubation of AtT-20 cells with Rolipram along with inhibitors of type I (but not of type III) PDEs, enhanced cAMP formation elicited by PACAP to a level significantly higher than that induced by CRF.(ABSTRACT TRUNCATED AT 250 WORDS)

[Initial studies of the prevalence of human Herpesvirus 7 (HHV-7) in Mexican blood donors]

Human herpesvirus 7 (HHV-7) has been recently isolated from CD4-positive peripheral blood lymphocytes of a healthy person. The present study was performed to find the antibody prevalence of this virus in the healthy Mexican population. Two hundred blood samples from candidates for blood donation at the General Hospital of Mexico were studied with the indirect immunofluorescence test (IFA) in HHV-7 infected SupT1 cells. 83.5% were male persons and 16.5% female, the mean age for the male group was 28.8 years and for the female group 31.5. The donors came from 12 different states in Mexico, predominantly from the city (60.8%), and had different occupations. Almost all samples (98.5%) were positive to HHV-7. Other studies done revealed 1% positive to brucella, 1% positive to Hepatitis B, 2% positive to syphilis, hepatitis C and HIV test were negative in the whole group studied. There was a high incidence of HHV-7 in the group studied: more than 50% of the subject had high titers. This results should be further studied determine titers indicative of an active infection and to search for any association with illnesses.

[Apoptosis and cell proliferation in HHV-6 infections. Regulatory mechanisms of p53/bcl-2/ras interactions]

HHV-6 infected immature T (HSB2) and Hodgkin (HDLM2) cells and biopsy tissues from lymph nodes of patients with Hodgkin's disease (HD) and Kikuchi lymphadenitis (KL) were studied immunohistologically for virus antigen expression and for the oncogene/anti-oncogene products ras, bcl-2 and p53. Cell proliferation and cell death were tentatively monitored in tissue culture by PCNA staining, by viability testing and in situ end labeling of fragmented DNA. PCNA was also used in biopsy samples. KL is characterized by high incidences of focal cell death (i.e. histiocytic necrotizing lymphadenitis), while HD is apparently more a proliferative disease. The techniques used revealed no significant differences in the cellular expression of viral DNA or antigens among cell lines, HD or KL. The HDLM2 cell line with the superior survival after HHV-6 infection showed a significantly lower expression of p53 and PCNA than HSB2 cells. Biopsy samples from patients with KL did not express p53, and ras and PCNA were observed in fewer cells than in HD. Bcl-2, however, was significantly more frequently seen than in HD. The interpretation of the data is difficult; they suggest that there are additional regulatory influences in control of cell proliferation and cell death, such as cytokines and growth factors, which are altered after viral infection. Also, virus-induced cell death probably includes other mechanisms besides apoptosis, such as cell damage caused by oxygen radicals.

Cytochrome P-450TYR is a multifunctional heme-thiolate enzyme catalyzing the conversion of L-tyrosine to p-hydroxyphenylacetaldehyde oxime in the biosynthesis of the cyanogenic glucoside dhurrin in Sorghum bicolor (L.) Moench

Cytochrome P-450TYR, which catalyzes the N-hydroxylation of L-tyrosine in the biosynthesis of the cyanogenic glucoside dhurrin in Sorghum bicolor (L.) Moench has recently been isolated (Sibbesen, O., Koch, B., Halkier, B. A., and Møller, B. L. (1994) Proc. Natl. Acad. Sci. U.S.A. 92, 9740-9744). Reconstitution of the enzyme activity in lipid micelles containing cytochrome P-450TYR and NADPH-cytochrome P-450 oxidoreductase demonstrates that cytochrome P-450TYR catalyzes the conversion of L-tyrosine into p-hydroxyphenylacetaldehyde oxime. Earlier studies with microsomes have demonstrated that this conversion involves two N-hydroxylation reactions of which the first produces N-hydroxytyrosine. We propose that the product of the second N-hydroxylation reaction is N,N-dihydroxytyrosine. N,N-dihydroxytyrosine is dehydrated to 2-nitroso-3-(p-hydroxyphenyl) propionic acid which decarboxylates to p-hydroxyphenylacetaldehyde oxime. The dehydration and decarboxylation reactions may proceed non-enzymatically. The E/Z ratio of the p-hydroxyphenylacetaldehyde oxime produced by reconstituted cytochrome P-450TYR is 69:31. Lipid micelles made from L-alpha-dilauroyl phosphatidylcholine are more than twice as effective in reconstituting cytochrome P-450TYR activity as compared to other lipids. The Km and turnover number of the enzyme is 0.14 mM and 200 min-1, respectively, when assayed in the presence of 15 mM NaCl whereas the values are 0.21 mM and 230 min-1 when assayed in the absence of added salt. The multifunctional nature cytochrome P-450TYR is confirmed by demonstrating that binding of L-tyrosine or N-hydroxytyrosine mutually excludes binding of the other substrate. These results explain why the conversion of tyrosine to p-hydroxyphenylacetaldehyde oxime as earlier reported (Møller, B. L., and Conn, E. E. (1980) J. Biol. Chem. 255, 3049-3056) shows the phenomenon of catalytic facilitation ("channeling"). Cytochrome P-450TYR is the first isolated multifunctional heme-thiolate enzyme from plants. N-Hydroxylases of the cytochrome P-450 type with high substrate specificity have not previously been reported.

Characterization of cytochrome P450TYR, a multifunctional haem-thiolate N-hydroxylase involved in the biosynthesis of the cyanogenic glucoside dhurrin

The haem-thiolate N-hydroxylase cytochrome P450TYR involved in the biosynthesis of the tyrosine-derived cyanogenic glucoside dhurrin in Sorghum bicolor had recently been isolated. Reconstitution of enzyme activity by insertion of cytochrome P450TYR and NADPH-cytochrome P450-reductase into L-alpha-dilauroylphosphatidylcholine micelles and using tyrosine as substrate results in the formation of p-hydroxyphenylacetaldehyde oxime. Quantitative substrate binding spectra demonstrate that tyrosine and N-hydroxytyrosine are mutually exclusive substrates that bind to the same active site of cytochrome P450TYR. The multifunctionality of cytochrome P450TYR has been confirmed in reconstitution experiments using recombinant cytochrome P450TYR expressed in Escherichia coli. It was earlier reported that an in vitro microsomal system catalyzing all but the last step in the biosynthetic pathway for cyanogenic glucosides exhibits catalytic facilitation (channelling). This observation is explained by the multifunctionality of cytochrome P450TYR. The cytochrome P450TYR sequence represents the first amino acid sequence of a functionally characterized cytochrome P-450 enzyme from a monocotyledonous plant and the first sequence of an N-hydroxylase with high substrate specificity. Multifunctional N-hydroxylases of the cytochrome P-450 type have not previously been reported in living organisms.