[Multiple endocrine neoplasia type III: report of three cases]

Multiple endocrine neoplasia type III (MEN III), or MEN IIb, is a rare syndrome. We have reported 3 typical cases of MEN III since 1987. Their syndrome was characterized by striking appearance of marfanoid habitus and face, multiple mucosal neuromas affecting lips and tongue, medullary thyroid carcinoma. Their family histories were negative. Only the third case of MEN III was correctly diagnosed before operation. Medullary thyroid carcinoma was removed. The first case was followed up for 7 years without recurrence.

Colony-stimulating factor-1 secreted by fibroblasts promotes the growth of dendritic cell lines (XS series) derived from murine epidermis

We have established recently from mouse epidermis long-term dendritic cell lines (XS series) that resemble epidermal Langerhans cells (LC) by their surface phenotype, Ag-presenting profile and cytokine mRNA profile. The growth of XS lines was promoted maximally by granulocyte-macrophage-CSF or by a factor secreted by NS lines, which are fibroblastic cell lines established from dispase-separated specimens of mouse epidermis. The purpose of this study was to determine the identity of XS cell growth factor secreted by NS cells. We report the following: 1) NS cells express constitutively mRNA for CSF-1; 2) XS cells express the CSF-1R at mRNA and protein levels; 3) rCSF-1 mimics NS culture supernatant in its ability to promote XS cell growth; 4) NS supernatant-dependent XS cell growth is blocked completely by each of two Abs against the CSF-1R. We conclude that CSF-1 is responsible for the XS growth-promoting activity secreted by NS lines. We also report the following: 5) LC freshly isolated from skin express CSF-1R mRNA; and 6) fibroblasts derived from specimens of dermis also express mRNA and secrete large amounts (50-100 ng/ml) of CSF-1. These observations give rise to a new concept that dermal fibroblasts may support the survival and growth of LC (and their precursors) through the paracrine effect of elaborated CSF-1.

Colony-stimulating factor-1 secreted by fibroblasts promotes the growth of dendritic cell lines (XS series) derived from murine epidermis

We have established recently from mouse epidermis long-term dendritic cell lines (XS series) that resemble epidermal Langerhans cells (LC) by their surface phenotype, Ag-presenting profile and cytokine mRNA profile. The growth of XS lines was promoted maximally by granulocyte-macrophage-CSF or by a factor secreted by NS lines, which are fibroblastic cell lines established from dispase-separated specimens of mouse epidermis. The purpose of this study was to determine the identity of XS cell growth factor secreted by NS cells. We report the following: 1) NS cells express constitutively mRNA for CSF-1; 2) XS cells express the CSF-1R at mRNA and protein levels; 3) rCSF-1 mimics NS culture supernatant in its ability to promote XS cell growth; 4) NS supernatant-dependent XS cell growth is blocked completely by each of two Abs against the CSF-1R. We conclude that CSF-1 is responsible for the XS growth-promoting activity secreted by NS lines. We also report the following: 5) LC freshly isolated from skin express CSF-1R mRNA; and 6) fibroblasts derived from specimens of dermis also express mRNA and secrete large amounts (50-100 ng/ml) of CSF-1. These observations give rise to a new concept that dermal fibroblasts may support the survival and growth of LC (and their precursors) through the paracrine effect of elaborated CSF-1.

Inducible nitric oxide synthase gene expression in brain following cerebral ischemia

Cerebral ischemia is followed by a local inflammatory response that is thought to participate in the extension of the tissue damage occurring in the postischemic period. However, the mechanisms whereby the inflammation contributes to the progression of the damage have not been fully elucidated. In models of inflammation, expression of the inducible isoform of nitric oxide synthase (iNOS) is responsible for cytotoxicity through the production of large amounts of nitric oxide (NO). In this study, therefore, we sought to establish whether iNOS is expressed in the ischemic brain. Rats were killed 6 h to 7 days after occlusion of the middle cerebral artery. iNOS expression in the ischemic area was determined by reverse-transcription polymerase chain reaction. Porphobilinogen deaminase mRNA was detected in the same sample and used for normalization. In the ischemic brain, there was expression of iNOS mRNA that began at 12 h, peaked at 48 h, and returned to baseline at 7 days (n = 3/time point). iNOS mRNA expression paralleled the time course of induction of iNOS catalytic activity, determined by the citrulline assay (17.4 +/- 4.4 pmol citrulline/micrograms protein/min at 48 h; mean +/- SD; n = 5 per time point). iNOS immunoreactivity was seen in neutrophils at 48-96 h after ischemia. The data provide molecular, biochemical, and immunocytochemical evidence of iNOS induction following focal cerebral ischemia. These findings, in concert with our recent demonstration that inhibition of iNOS reduces infarct volume in the same stroke model, indicate that NO production may play an important pathogenic role in the progression of the tissue damage that follows cerebral ischemia.

[Surgical treatment of avascular necrosis of the femoral head]

71 patients (83 hips) with avascular necrosis of the femoral head were followed up. The patients had bilateral necrosis (12), and unilateral (59). Their ages ranged from 19 to 71 years. Ficat classification showed stage I for 1 hip, stage II 19 hips, stage III 35 hips, and stage IV hips. According to the severity, the range of motion, the age, and the X-ray appearances, 6 kinds of procedures were used including decompression with bone grafting (32 hips), surface arthroplasty with cartilage (4), surface arthroplasty with fascia (4), replacement of femoral head (7), THA (20), and obturator neuroetomy (16). The follow-up period ranged from 2 years and 3 months to 10 years and 5 months. Postoperative improvement included pain (39.7%), range of motion (21.7%), and walking (33.7%). Among the procedures, decompression with bone grafting showed best results. Treatment revealed better results in stage I, II than in stage III, IV. We emphysize the early diagnosis and management, and choice of procedure should base on the clinical classification.

VH and VL gene usage by anti-beta-amyloid autoantibodies in Alzheimer's disease: detection of highly mutated V regions in both heavy and light chains

In a previous study, four human IgM kappa monoclonal antibodies (mAbs) secreted by Epstein-Barr-virus-transformed B cell lines independently derived from the peripheral blood of a patient with Alzheimer's disease (AD) were found to react with a conformational epitope of beta-amyloid protein and to stain amyloid plaques in AD brain. Three of these mAbs were studied further. They did not react with an additional panel of antigens and autoantigens. By a competitive inhibition ELISA, the Kd was determined to be 5.7 x 10(-8) M. The VH and V kappa of these mAbs were sequenced at the cDNA level and found to be identical. The corresponding VH and V kappa germline counterpart genes hsigghvm148 and hsiggkvm148 were identified to be analogous to the previous reported VH3 germline gene humighvf1/dp53 and the V kappa IV germline gene hsigk18. DA1/4 and JH4b were used by the heavy chain and J kappa 4 was used by the light chain. Multiple nucleotide substitutions were seen in both VH and V kappa when their sequences were compared to the germline sequences. High replacement/silent ratios in the CDR regions of both VH and V kappa indicate positive-selective pressure. Of a total of 22 amino acid replacements in VH and V kappa, 12 were nonconservative replacements. Furthermore, 7 of these 12 resulted in charge changes. The monoreactivity, the moderately high affinity constant, the clonal expansion evident by identical VH and VL used by these B cells secreting antibodies of interest, and the excessive replacement mutations in both VH and VL segments lead to the conclusion that these antibodies have been generated due to an antigen-driven process.

Measurement of water diffusion in hormone-treated rat uteri by diffusion-weighted magnetic resonance imaging

In this study, apparent water diffusion coefficients in hormone-treated rat uteri were measured by diffusion-weighted NMR imaging. Four groups of ovariectomized, mature young rats were treated with estrogen, progesterone, estrogen plus progesterone, or saline (as control). It was found that water diffusion is anisotropic in the myometrium, but not in the endometrium, and that it depends on hormonal conditions in the endometrium, but not in the myometrium. The anisotropy of water diffusion can be exploited to improve image contrast among the various uterine tissue types. The hormonal response suggests that diffusion imaging of human uterus may be useful in detecting endometrial pathology.

Roles of URE2 and GLN3 in the proline utilization pathway in Saccharomyces cerevisiae

The yeast Saccharomyces cerevisiae can use alternative nitrogen sources such as arginine, urea, allantoin, gamma-aminobutyrate, or proline when preferred nitrogen sources like glutamine, asparagine, or ammonium ions are unavailable in the environment. Utilization of alternative nitrogen sources requires the relief of nitrogen repression and induction of specific permeases and enzymes. The products of the GLN3 and URE2 genes are required for the appropriate transcription of many genes in alternative nitrogen assimilatory pathways. GLN3 appears to activate their transcription when good nitrogen sources are unavailable, and URE2 appears to repress their transcription when alternative nitrogen sources are not needed. The participation of nitrogen repression and the regulators GLN3 and URE2 in the proline utilization pathway was evaluated in this study. Comparison of PUT gene expression in cells grown in repressing or derepressing nitrogen sources, in the absence of the inducer proline, indicated that both PUT1 and PUT2 are regulated by nitrogen repression, although the effect on PUT2 is comparatively small. Recessive mutations in URE2 elevated expression of the PUT1 and PUT2 genes 5- to 10-fold when cells were grown on a nitrogen-repressing medium. Although PUT3, the proline utilization pathway transcriptional activator, is absolutely required for growth on proline as the sole nitrogen source, a put3 ure2 strain had somewhat elevated PUT gene expression, suggesting an effect of the ure2 mutation in the absence of the PUT3 product. PUT1 and PUT2 gene expression did not require the GLN3 activator protein for expression under either repressing or derepressing conditions. Therefore, regulation of the PUT genes by URE2 does not require a functional GLN3 protein. The effect of the ure2 mutation on the PUT genes is not due to increased internal proline levels. URE2 repression appears to be limited to nitrogen assimilatory systems and does not affect genes involved in carbon, inositol, or phosphate metabolism or in mating-type control and sporulation.

Endogenous porphyrins in murine skin and transplanted PAM-212 squamous cell carcinoma tissues after injection of delta-aminolevulinic acid

After intraperitoneal (IP) injection of delta-aminolevulinic acid (ALA), the endogenous porphyrins in murine skin and tumor tissues were determined by a method involving solvent and acid extractions. The results showed that the total amount of porphyrins in the tumor tissues after ALA injection was much higher than that in the skin from the same mice, although the amount of porphyrins in the skin from the ALA-injected mice was higher than that from the saline-injected (control) mice. The porphyrins in the tumor were mostly protoporphyrin and coproporphyrin, with only a small amount of uroporphyrin. The optimum period for porphyrin accumulation in the tumor as well as in the skin was 1 hour after the injection of ALA. As the period was extended to 3 and 6 hours, the amount of porphyrins in these tissues decreased considerably. These findings could be valuable for further application of ALA in the photodynamic therapy of skin cancer.

Cytokine-dependent regulation of growth and maturation in murine epidermal dendritic cell lines

We have recently established dendritic cell (DC) lines (XS series) from the epidermis of newborn mice by repeated feeding with granulocyte/macrophage-colony-stimulating factor (GM-CSF) and culture supernatants from skin-derived stromal cell lines (NS series). XS lines resemble resident Langerhans cell (LC), which are immature DC that reside in epidermis, by their surface phenotype and antigen-presenting profile. XS lines further resemble resident LC in that they express mRNA for interleukin-1 beta and macrophage inflammatory protein (MIP)-1 alpha, and by the absence of mRNA for IL-6. Their growth is promoted by GM-CSF, colony-stimulating factor-1 (CSF-1), or NS culture supernatant, and inhibited by interferon-gamma or tumor necrosis factor-alpha. The expression by the XS lines of Ia molecules is up-regulated by GM-CSF, and down-regulated by NS supernatant. These results suggest the existence of negative regulatory mechanisms in which the growth and/or maturation of DC is suppressed by selected cytokines.

[The diagnostic value of cortical evoked potential in spinal cord injury]

From 1983-1992 CEP monitoring in spinal cord injury (SCI) was performed in 312 cases, of them 9 were acute SCI and 303 chronic (cervical spine 57, dorsal 88, T11-L1 136 and lumbar 31). 179 cases were complete paraplegia and 133 incomplete paraplegia. CEP were negative in 175 of 179 complete paraplegia, and the correct diagnosis rate was 97.8%. The false positive rate was 2.2%. The changes of CEP in 133 cases of incomplete paraplegia were prolonged latent period and/or decrease in amplitude. Negative CEP occurred in 5 cases, making the false negative rate to be 3.75%. In case of cervical SCI, the CEP of median nerve was positive when C5 segment was intact, while radial nerve CEP was positive as C6 segment was intact. The ulnar nerve CEP was mostly involved in lower cervical spine injury and in central type of SCI because it is composed of C7, C8 and T1 segments. In dorso-lumbar junction, there was the lower end of the spinal cord with its nerve roots, therefore, the CEP of T11-L1 SCI was performed by stimulating femoral, posterior tibial and common peroneal nerves to decrease false negative rate in incomplete paraplegia. Positive CEP in the femoral nerve and negative in tibial and peroneal nerves indicate recovery of nerve roots of lumbar plexus and no recovery of the spinal cord. Positive CEP in femoral, tibial and peroneal nerves represents recovery of the spinal cord and its roots and negative CEP in all three nerves indicate complete SCI, no recovery of spinal cord and its roots.(ABSTRACT TRUNCATED AT 250 WORDS)

Successive generation of antigen-presenting, dendritic cell lines from murine epidermis

Dendritic cells are specialized APCs that exhibit an extraordinary capacity to activate naive T cells. Langerhans cells (LC), as epithelial tissue-specific members of this family, play key roles in the induction of T cell-mediated immunity against environmental, infectious, and tumor-associated Ags in skin. A major limitation in studying the biology of dendritic cells or LC has been the absence of stable, long-term cell lines. To overcome this limitation, we have established a series of APC lines (XS series) from newborn BALB/c mouse epidermis. XS lines, which have grown for more than 12 mo in culture, exhibit high similarity to LC freshly procured from skin in terms of: a) tissue of derivation (epidermis), b) phenotype (lalow/CD45+/E-cadherin+/B7-1-), c) shape (elongated dendrites), and d) Ag-presenting profile (modest ability to activate naive, allogeneic T cells and remarkable ability to present a protein Ag to primed CD4+ T cells). The availability of XS lines as well as the methodologies used for their growth enhance our capability of studying the biology of LC at biochemical and molecular levels.

Successive generation of antigen-presenting, dendritic cell lines from murine epidermis

Dendritic cells are specialized APCs that exhibit an extraordinary capacity to activate naive T cells. Langerhans cells (LC), as epithelial tissue-specific members of this family, play key roles in the induction of T cell-mediated immunity against environmental, infectious, and tumor-associated Ags in skin. A major limitation in studying the biology of dendritic cells or LC has been the absence of stable, long-term cell lines. To overcome this limitation, we have established a series of APC lines (XS series) from newborn BALB/c mouse epidermis. XS lines, which have grown for more than 12 mo in culture, exhibit high similarity to LC freshly procured from skin in terms of: a) tissue of derivation (epidermis), b) phenotype (lalow/CD45+/E-cadherin+/B7-1-), c) shape (elongated dendrites), and d) Ag-presenting profile (modest ability to activate naive, allogeneic T cells and remarkable ability to present a protein Ag to primed CD4+ T cells). The availability of XS lines as well as the methodologies used for their growth enhance our capability of studying the biology of LC at biochemical and molecular levels.

Multistage selection for maximum economic return with an application to beef cattle breeding

Methodology for selection index updating was developed to allow multistage selection. The program determines truncation points for each stage of selection that will maximize either profit or the ratio of aggregate economic gain to cost (R = delta H/C). Either maximum profit or R may be attained by reducing the cost of performance testing in later stages of a multistage program. In order to eliminate the need for multiple integration and assure convergence, a piecewise algorithm was developed. Examples of beef bull selection compared single-stage selection at 1 yr of age, two-stage selection at birth and 1 yr, two-stage selection at 205 d and 1 yr, and three-stage selection at birth, 205 d, and 1 yr. Selection based on three traits (birth weight, gain birth to 205 d, and gain 205 to 365 d) was compared with selection based on four traits (the above three plus ultrasound fat depth) and selection based on five traits (the above four plus feed:gain ratio). Five scenarios were used that allowed variation in proportion of candidates selected for breeding, number of progeny per selected bull, and proportion of profit returned to the nucleus herd. General conclusions based on the examples were 1) multistage selection reduced aggregate economic gain relative to that attained by single-stage selection, 2) inclusion of feed conversion in the index of traits resulted in reduced profit and aggregate economic gain, 3) measurement of feed conversion could be justified when selected bulls produced a large number of progeny, and 4) three-trait selection produced greater profit in all five scenarios than did four- or five-trait selection. Use of the selection updating program described here provides a new source of information that can be used in developing economically sound performance testing and selection programs.

Clinical value of urinary and serum pseudouridine in diagnosis and monitoring of primary liver cancer

Urinary and serum pseudouridine concentrations were determined by high-performance liquid chromatography in 80 patients with primary liver cancer, 32 with benign space occupying lesions of the liver, 42 with liver cirrhosis and 40 healthy subjects. Their mean urinary and serum pseudouridine levels were 39.2 +/- 11.5 nmol/mumol creatinine and 3.4 +/- 1.3 mumol/L, 24.5 +/- 5.4 nmol/mumol creatinine and 2.5 +/- 0.5 mumol/L, 22.8 +/- 7.8 nmol/mumol creatinine and 2.3 +/- 0.4 mumol/L, 26.4 +/- 4.6 nmol/mumol creatinine and 2.3 +/- 0.4 mumol/L, respectively. Exceeding the mean plus 2SD of pseudouridine of healthy control was considered as positive value for the diagnosis of primary liver cancer. Thus the positivity of urinary and serum pseudouridine in hepatoma was 71.3% and 70.0%, respectively. The positive rate of combined pseudouridine and alpha-fetoprotein assay was 91.3% in patients with hepatoma. Besides, pseudouridine levels could elevate before positive localization and reduce to normal levels after tumor resection. The results showed that the determination of pseudouridine is of clinical significance in the diagnosis and monitoring of primary liver cancer.

[Nationwide survey of the distribution of human parasites in China--infection with parasite species in human population]

The infection rate of main species of parasites and their character by first nationwide survey of human parasites was made. The overall infection rate of human intestinal parasite and the infection rate of most species of parasites were higher in females than that in males. The infection rate according to the age group, the highest infection rate was found in the group aged 5-14 years. With regard to the relation between parasitic infections and occupations of the infected persons, the highest infection rates of Ascaris lumbricoides were exhibited in school children, of hookworm and Clonorchis sinensis were in halfpeasants and halfmerchant and vegetable grower; of Trichuris trichiura were in fishers, of Giardia lamblia, Entamoeba histolytica and Taenia were in herdsmen and halfherdsmen and halfpeasants. In this survey it is also shown that each nationality has their main species of parasites. The family clustering of some main parasites were proved by some province/autonomous region/municipality.

[Characteristics and recent trends in endemicity of human parasitic diseases in China]

An analysis of the nationwide survey of the distribution of human parasites in the light of the literature previously published, two major trends in the endemicity of parasitic diseases in China was observed. For one trend, the infection rate of E. histolytica, Fasciolopsis buski and soil-transmitted helminthasis etc. declined markedly. The second trend was that the prevalence of food-transmitted parasitic diseases (Trichinella spiralis, Clonorchis sinensis, Paragonimiasis, cysticercosis) and hydatidosis was increasing. The relationship between the social economic factors and the two trends were discussed.

Tissue IGFBP-3 proteolysis: contrasting pathophysiology to that in the circulation

Endogenous IGFBP-3 has been examined in the circulation and in four different extravascular fluids in normal healthy adults and in patients with psoriasis or arthritis. In all of these cases there was no apparent increase of IGFBP-3 protease activity in the circulation. In contrast, endogenous IGFBP-3 from normal skin interstititial fluid and synovial fluid from healthy adults was found to be predominantly in the 29 kDa proteolytically modified form. This indicated that in these extravascular fluids in normal healthy adults a protease was active which was similar, if not identical, to that found in the circulation in pregnancy and other conditions. This was confirmed by the fragmentation of recombinant IGFBP-3 when incubated with these fluids. When the skin interstitial fluid or synovial fluid were taken from abnormal tissues (psoriasis in the former and osteoarthritis or rheumatoid arthritis in the latter) there was a considerable reduction in the amount of endogenous IGFBP-3 in the 'clipped' form and a reduction in the protease activity. In psoriatic lesions, this reduction in IGFBP-3 protease activity was shown to be due to the presence of an inhibitor in the interstitial fluid but not in the circulation. In both peritoneal and follicular fluid, the ratio of intact to fragmented IGFBP-3 appeared to relate to the oestrogen status. In peritoneal fluid there was a decrease in intact IGFBP-3 during the late proliferative/early secretory phase of the endometrial cycle. In the ovary there was an increase in the amount of fragmented IGFBP-3 in the follicular fluid from the dominant follicle in comparison with atretic follicles from the same ovary. There is normally little proteo-lysis of IGFBP-3 in the circulation but this increases in many conditions where there is increased metabolic activity. The same enzyme(s) appear to be active in many extravascular fluids but under very different regulation. The activity in these extravascular fluids is normally high but can be decreased with local tissue inflammation; this decrease appears to be mediated by the induction of a local inhibitor.

Increased vulnerability of hypertrophied myocardium to ischemia and reperfusion injury. Relation to cardiac renin-angiotensin system

Hearts of pressure-overload hypertrophy show an increased activation of intracardiac renin-angiotensin system which may contribute to ischemia and reperfusion injury. The purpose of this study is to evaluate whether the hypertrophied myocardium is more vulnerable to ischemia and reperfusion injury and to find out its relation to the cardiac renin-angiotensin system. Hypertrophied rat hearts induced by abdominal aortic banding for 6 weeks were subjected to 2 hours of hypothermic ischemic arrest followed by 30 minutes of reperfusion, and their cardiac function recovery was compared with that of sham-operated normal control hearts. The cardiac renin activity and angiotensin II content before ischemia and after reperfusion were determined. It was found that both the pre-ischemic renin activity and angiotensin II level were higher in hypertrophied myocardium than those in the control: ischemia and reperfusion injury increased both renin activity and angiotensin II content in the two groups, but the renin activity and angiotensin II level were further elevated after reperfusion in the hypertrophied hearts than those in the control hearts. Meanwhile, the cardiac function recovery after 30 minutes reperfusion in the hypertrophied hearts was poorer than that in the control. Correlation analysis revealed that there was a negative correlation between the cardiac output recovery and the myocardial angiotensin II content (r = -0.8411, P < 0.001). It is concluded that ischemia and reperfusion injury can activate cardiac renin-angiotensin system in isolated rat heart, which may be responsible for the increased susceptibility of the hypertrophied myocardium to ischemia and reperfusion injury.

Glycoluril

The crystal structure of glycoluril [tetrahydroimidazo-[4,5-d]imidazole-2,5(1H,3H)-dione, C4H6N4O2] has been determined. The molecule has two equivalent planes containing urea moieties, and hence exhibits C2v symmetry. The dihedral angle is found to be 124.1 (4) degrees.

Phylogenetic inference under the pure drift model

When pairwise genetic distances are used for phylogenetic reconstruction, it is usually assumed that the genetic distance between two taxa contains information about the time after the two taxa diverged. As a result, upon an appropriate transformation if necessary, the distance usually can be fitted to a linear model such that it is expressed as the sum of lengths of all branches that connect the two taxa in a given phylogeny. This kind of distance is referred to as "additive distance." For a phylogenetic tree exclusively driven by random genetic drift, genetic distances related to coancestry coefficients (theta XY) between any two taxa are more suitable. However, these distances are fundamentally different from the additive distance in that coancestry does not contain any information about the time after two taxa split from a common ancestral population; instead, it reflects the time before the two taxa diverged. In other words, the magnitude of theta XY provides information about how long the two taxa share the same evolutionary pathways. The fundamental difference between the two kinds of distances has led to a different algorithm of evaluating phylogenetic trees when theta XY and related distance measures are used. Here we present the new algorithm using the ordinary-least-squares approach but fitting to a different linear model. This treatment allows genetic variation within a taxon to be included in the model. Monte Carlo simulation for a rooted phylogeny of four taxa has verified the efficacy and consistency of the new method. Application of the method to human population was demonstrated.

Interaction of tubulin with guanosine 5'-O-(1-thiotriphosphate) diastereoisomers: specificity of the alpha-phosphate binding region

The exchangeable nucleotide-binding site of tubulin has been studied using diastereoisomers A (Sp) and B (Rp) of guanosine 5'-O-(1-thiotriphosphate) (GTP alpha S) in which the phosphorus atom to which sulfur is attached is chiral. GTP alpha S(A) (10 microM) nucleated assembly of purified tubulin (20 microM) into microtubules in buffer containing 0.1 M 2-(N-morpholino)ethanesulfonic acid with 3 mM Mg2+ and 1 mM EGTA, pH 6.6 at 37 degrees C. With 0.2 mM GTP alpha S(A), the critical concentration (Cc; minimum protein concentration required for assembly) was 8 microM tubulin. Neither 0.2 mM GTP nor GTP alpha S(B) promoted microtubule assembly in buffer with 0.5-6.75 mM Mg2+ and 20-70 microM tubulin. The Cc values for GTP alpha S-(A)-induced assembly of tubulin in buffer with 30% glycerol and of microtubule protein (tubulin and microtubule-associated proteins) in buffer were lower than for GTP. GTP alpha S(A)-induced microtubules were more stable to the cold and to Ca2+. GTP alpha S(A) and GTP but not GTP alpha S(B) bound tightly to tubulin at 4 degrees C. Although GTP alpha S(B) did not nucleate assembly, it did bind to tubulin since it was incorporated into the growing microtubule. Both isomers were hydrolyzed in the microtubules. These studies show that GTP alpha S(A) promotes tubulin assembly better than GTP and GTP alpha S(B) and that there is stereoselectivity at the alpha-phosphate binding region of tubulin. The stereoselectivity may be due to different MgGTP alpha S(A) and -(B) interactions with tubulin.