Preliminary evaluation of color Doppler imaging for investigation of intrascrotal pathology

Color Doppler ultrasound facilitates investigation of blood flow in addition to imaging parenchymal abnormalities. To assess the clinical use of this technique we evaluated 25 consecutive patients with indications for intrascrotal imaging. Color flow imaging added useful information in all 11 patients evaluated for chronic scrotal pain and in 6 of 7 evaluated for acute scrotal pain. In contrast, color flow ultrasound provided little additional information in 7 patients with intrascrotal masses. Color flow ultrasound imaging is a promising method that may prove to be useful for assessment of selected patients with intrascrotal pathological conditions.

Overexpression of virD1 and virD2 genes in Agrobacterium tumefaciens enhances T-complex formation and plant transformation

The VirD1 and VirD2 proteins encoded by an inducible locus of the virulence (vir) region of the Agrobacterium tumefaciens Ti plasmid are required for site-specific nicking at T-DNA border sites. We have determined the nucleotide sequence of a 3.6-kilobase-pair fragment carrying the virD locus from nopaline Ti plasmid pTiC58. In contrast to the previous report (Hagiya et al., Proc. Natl. Acad. Sci. USA 82:2669-2673, 1985), we found that the first three open reading frames were capable of encoding polypeptides of 16.1, 49.7, and 21.4 kilodaltons. Deletion analysis demonstrated that the N-terminal conserved domain of VirD2 was absolutely essential for its endonuclease activity. When extra copies of the virD1 and virD2 genes were present in an A. tumefaciens strain carrying a Ti plasmid, increased amounts of T-strand and nicked molecules could be detected at early stages of vir induction. Such strains possessed the ability to transform plants with higher efficiency.

The Pyridium pad test for diagnosing urinary incontinence. A comparative study of asymptomatic and incontinent women

Eighteen women with urodynamically proven genuine stress incontinence awaiting surgery and 23 normal, asymptomatic, continent female volunteers took part in a study to compare the accuracy of a qualitative pad test with a quantitative pad-weighing test in detecting urine loss. Each woman took 600 mg of phenazopyridine hydrochloride (Pyridium, Parke-Davis) in three equally divided doses over 18-24 hours and then underwent a standardized, one-hour pad test as described by the International Continence Society. The Pyridium pad test was regarded as positive if there was any orange staining on the pad. The quantitative pad-weighing test was considered positive if there was a weight gain of 1.0 g or more at the end of the one-hour test period. All 18 patients with genuine stress incontinence had positive Pyridium pad tests, and all had pad weight gains of greater than or equal to 1.0 g (mean, 16.5). The maximum pad weight gain in the asymptomatic, continent volunteers was 0.7 g (mean, 0.1), and none was aware of any urinary leakage during the test; however, 12 (52%) had positive Pyridium pad tests. The Pyridium pad test appears 100% sensitive in detecting urine loss in symptomatic women with genuine stress incontinence, but it has a high false-positive rate in healthy, asymptomatic, continent women. If pad-weighing tests are done, the addition of Pyridium generally will not be useful, and if Pyridium is used by itself, the results may be misleading.

Cell-mediated immune responses to poliovirus II. Survey of delayed hypersensitivity and T-cell proliferative responses in inbred mouse strains

Some epidemiological reports suggest a human genetic predisposition for susceptibility to the development of paralytic poliomyelitis. In a previous study of cell-mediated immune responses by mice to poliovirus (PV), we showed differences in the responses by BALB/c and C57BL/6 (B6) mice. The present study is a further analysis of the delayed hypersensitivity (DTH) and T cell proliferative (Tprlf) responses to PV in 17 different inbred strains of mice, to determine if these responses were under major histocompatibility complex (MHC) or other genetic control. Both DTH and Tprlf to PV did not correlate with MHC for responses to any of the three PV serotypes. Further, we found a lack of concordance of DTH and Tprlf responses to a given PV serotype. The cell-mediated immune responses by any one mouse strain to one PV serotype is not predictive of that mouse strain's response to another PV serotype.

Correlation of intraoperative ultrasound tumor volumes and margins with preoperative computerized tomography scans. An intraoperative method to enhance tumor resection

Twenty-two patients with primary or metastatic brain tumors were evaluated with computerized tomography (CT) and intraoperative ultrasound. Tumor volume was estimated using a geometric formula based on CT and intraoperative ultrasound measurements. In most cases, tumor margins were marked with indigo carmine injected by ventricular cannula or with Silastic ventricular catheters placed under ultrasonographic control. Nine tumors had previously been operated on and irradiated (Group A). In this group, intraoperative ultrasound tended to overestimate the tumor volume compared to CT (intraoperative ultrasound findings 141.39% +/- 37.73% of CT findings (mean +/- standard deviation]. Sixteen patients were operated on for the first time (Group B), and in this group the volume estimates were comparable (intraoperative ultrasound findings 101.69% +/- 24.65% of CT findings). The difference between the means was statistically significant (p less than 0.01). Ultrasonography improved intraoperative delineation of tumor margins, as depicted by CT, thus maximizing the extent of resection; however, with recurrent tumors, intraoperative ultrasound tended to overestimate the tumor volume. Gliosis may account for this difference.

Kinetic studies of mobilization of copper(II) from human serum albumin with chelating agents

The kinetics of the mobilizing reactions of five chelating agents for human serum albumin (HSA)-bound copper(II) [Cu(II)] have been studied spectrophotometrically. The decreasing sequence of reaction rate has been determined to be EDTA greater than DTPA greater than EGTA greater than NTA greater than IDA. A group of mathematical models were established to define the mechanisms of the competitive reactions between low-molecular-weight ligand and macromolecular ligand. All reactions of the five chelating agents follow a process involving the intermediate ternary complexes: (formula; see text) The reactions of DTPA and EDTA were found to be different from those of EGTA, NTA, and IDA. In the former cases, the reactions are likely following an overlapping mechanism in which the rate constant k1 was closed to k2. The reactions involving the other three chelators are different in k1 much greater than k2.

Needling sensation receptor of an acupoint supplied by the median nerve--studies of their electro-physiological characteristics

We classified 50 receptor units from 10 acupoints supplied by the medium nerve. It was found that the needling stimulation mostly excited slowly adapting receptors and that the classification of acupoint receptors related closely to their location. For example, the Shanyang, Zhongchong, Shaoshang acupoints in the skin needling sensation receptors are touch or pressure receptor units; the receptors of Neiguan, Yuji, etc.; the acupoints located in deep tissue with abundant muscles, are mostly muscle spindles; the Daling acupoint might be a colgi tendon and/or pressure receptor unit. Besides a significant receptor, an acupoint contains one or more needling sensation receptor. The receptors and the afferent fibers of acupoints take part in forming and maintaining the needling sensations.

VirD proteins of Agrobacterium tumefaciens are required for the formation of a covalent DNA-protein complex at the 5′ terminus of T-strand molecules

The T-DNA transfer process of Agrobacterium tumefaciens is activated by the induction of the Ti plasmid virulence (vir) loci by plant signal molecules such as acetosyringone. Upon initiation of the T-DNA transfer process, site-specific nicks occur at the 25-bp border sequences. This cleavage leads to the generation of a free, linear ssT-DNA molecule which is bound by sequence non-specific VirE proteins. Here we present evidence for the involvement of other acetosyringone-induced proteins in the formation of a covalent complex between the T-strand and protein, designated the T-complex. Alkaline gel-electrophoretic analysis showed that proteins specifically bind to the 5' termini of nicked T-DNA molecules. The T-complex can be formed in Escherichia coli when the VirD1 and VirD2 proteins are expressed.

Glycine betaine allows enhanced induction of the Agrobacterium tumefaciens vir genes by acetosyringone at low pH

We established growth conditions for efficient induction of the vir genes of Agrobacterium tumefaciens by acetosyringone. Optimal induction was attained at a pH below 5.2 in an AB minimal medium-derived high-osmotic-strength medium containing glycine betaine. This natural osmoprotectant accelerated the adaptation of the bacteria to these conditions. We established the kinetics of induction for virB, virD, virE, and virG by using lacZ fusions, and we found that the virB mutant strain could not adapt to this low-pH medium unless 1 mM CaCl2 was added. This pH control of vir gene expression was shown to act at the level of expression of virG, which was the limiting factor. This improved vir induction at a low pH correlated with an increase in a set of proteins which was analyzed by two-dimensional gel electrophoresis. The fact that high inducibility corresponded to a reduced growth rate and the demonstration that a set of proteins was associated with the inducible state suggest that vir gene induction is linked to the adaptation of the cells to an unfavorable environment. Hence, vir gene expression in A. tumefaciens is probably dependent upon a machinery which is specific to an adaptive response; the implications for plant transformation are discussed.

Architecture of the sarcomere matrix of skeletal muscle: immunoelectron microscopic evidence that suggests a set of parallel inextensible nebulin filaments anchored at the Z line

Nebulin, a giant myofibrillar protein (600-800 kD) that is abundant (3%) in the sarcomere of a wide range of skeletal muscles, has been proposed as a component of a cytoskeletal matrix that coexists with actin and myosin filaments within the sarcomere. Immunoblot analysis indicates that although polypeptides of similar size are present in cardiac and smooth muscles at low abundance, those proteins show no immunological cross-reactivity with skeletal muscle nebulin. Gel analysis reveals that nebulins in various skeletal muscles of rabbit belong to at least two classes of size variants. A monospecific antibody has been used to localize nebulin by immunoelectron microscopy in a mechanically split rabbit psoas muscle fiber preparation. Labeled split fibers exhibit six pairs of stripes of antibody-imparted transverse densities spaced at 0.1-1.0 micron from the Z line within each sarcomere. These epitopes maintain a fixed distance to the Z line irrespective of sarcomere length and do not exhibit the characteristic elastic stretch-response of titin epitopes within the I band domain. It is proposed that nebulin constitutes a set of inextensible filaments attached at one end to the Z line and that nebulin filaments are in parallel, and not in series, with titin filaments. Thus the skeletal muscle sarcomere may have two sets of nonactomyosin filaments: a set of I segment-linked nebulin filaments and a set of A segment-linked titin filaments. This four-filament sarcomere model raises the possibility that nebulin and titin might act as organizing templates and length-determining factors for actin and myosin respectively.

A preliminary report on transplantation of microskin autografts overlaid with sheet allograft in the treatment of large burns

The technique of transplantation of autologous microskin grafts (MG) with overlays of split-thickness skin allografts was used in the treatment of nine extensively burned patients. Preparation of MG includes: 1) mincing small pieces of split-thickness skin autografts into skin particles (SPs); 2) dispersing the SPs evenly on a piece of silk cloth; 3) transferring SPs to the dermal surface of an allograft sheet (20/1000 in.); 4) transplanting the allograft with SPs to the excised wound. The mean burn area (total/3 degrees, mean +/- SEM) of this group was 74.9 +/- 16.6/62.1 +/- 18.1% TBSA (range 40 to 94/28 to 90%). The mean age was 27 years (range 19 to 38). Early staged excisions followed immediately by MG applications were performed on 35 large body sites, including extremities, chests plus abdomens and backs. The mean area excised and grafted with MG was 41.7 +/- 11.0% TBSA (range 26 to 62%). The average time for complete healing was about six to seven weeks postgrafting. Eight patients survived; one died of overwhelming pulmonary infection 22 days postburn. Advantages of this technique are: 1) the great potential of MG to provide a large expansion ratio of 8:1 to 15:1, average greater than 10:1 in this series; 2) good maintenance of the healed graft to withstand trauma except in areas of repeated flexion; 3) ease of preparation and application with less cost compared to cultured epidermal sheet grafts; 4) prevention of infection in extremely large burns by providing continuous epidermal coverage following sheet allograft application.

Titin: quantitative mass measurements by scanning transmission electron microscopy and structural implications for the sarcomere matrix of skeletal muscle

Scanning transmission electron microscopy has been used to investigate mass and linear mass density of native titin-2, a large soluble fragment of intact titin, from rabbit skeletal muscle. Dark field images of unstained, freeze-dried titin-2 appeared as either compact globules or looser and larger balls of string. Direct mass measurements indicated that the compact forms have an average mass of 2.40 +/- 0.50 x 10(6) Da. The mass to length ratio, determined from well-spread portions of titin strands (3-5 nm wide) from the ball of string forms, averaged 2.7 +/- 0.9 kDa/nm. Thus a single native intact titin molecule has a calculated contour length of well above approximately 1 micron, sufficient to span unidirectionally between the Z line and M line region in a resting-length sarcomere.

Sarcomere matrix of striated muscle: in vivo phosphorylation of titin and nebulin in mouse diaphragm muscle

Titin and nebulin are two major protein components of a cytoskeletal matrix that coexists with thick and thin filaments within the sarcomere of a wide range of striated muscles. Purified titin and nebulin from mouse diaphragm muscle are similar in size, in relative abundance, and in amino acid composition to analogous proteins from other mammals or avians. Phosphate analysis of these nucleic-acid-free proteins indicated that both proteins contain substantial amounts of protein-bound phosphate: about 12 mol of phosphate per mole of titin subunit and 11 mol of phosphate per mole of nebulin subunit. Incubation of intact, excised mouse diaphragm with radioactive inorganic phosphate resulted in significant incorporation of radiophosphate into titin and nebulin. The identification of titin and nebulin phosphorylation was facilitated by a simple salt fractionation and nuclease digestion procedure that effectively separated titin and nebulin from radiolabeled nucleic acids. Such in vivo phosphorylation studies indicated that approximately 2 mol of phosphate per titin subunit and 5 to 7 mol of phosphate per nebulin subunit were incorporated within 5 h of incubation. The incorporation nearly doubled when the beta-adrenergic agonist, isoproterenol, or a phosphodiesterase inhibitor, theophylline, was present in the medium. For both proteins, phosphorylation occurred mainly on serine residues. Nebulin also appears to possess a smaller number of threonine sites. Taken together, our data indicate that a small proportion (20 to 40%) of the steady-state titin phosphates are rapidly turning over. In contrast, most of the nebulin phosphates (50 to 100%) are readily exchanged. The modulation of turnover by external stimuli that increase cytosolic cAMP raises the possibility that at least a portion of the multiple phosphorylation sites of titin and nebulin may be involved in the functional regulation of the sarcomere matrix.

Giant polypeptides of skeletal muscle titin: sedimentation equilibrium in guanidine hydrochloride

Titin has been purified from rabbit skeletal myofibrils in guanidine hydrochloride by gel filtration on Sephacryl S-1000. The sedimentation coefficients of denatured titin in 6 M guanidine hydrochloride are highly concentration dependent and follow the equation: 1/S = 0.241 + 0.302 A280. Equilibrium sedimentation studies indicate that the average molecular weight of titin polypeptides is 2.4 to 2.6 X 10(6).

Nebulin cDNAs detect a 25-kilobase transcript in skeletal muscle and localize to human chromosome 2

By virtue of the protein's size, myofibrillar localization, and proposed functional role, the gene encoding the giant sarcomere matrix protein nebulin represents a possible site for myopathic mutations. Using polyclonal anti-nebulin antisera to screen a cDNA expression library, we have isolated and characterized two separate human fetal muscle cDNA clones. By recovering fusion polypeptide-bound portions of our polyclonal antiserum and reutilizing them to probe Western blots, we further demonstrate that the expressed cDNAs encode polypeptide epitopes unique to the protein nebulin. Both cDNAs detect a 25-kb skeletal muscle RNA transcript and localize to human chromosome 2. The identification of nebulin cDNA clones enables the complete analysis of this enormous mRNA by transcript walking through muscle cDNA libraries. Here we report a restriction map of the 3' end of the human nebulin transcript, with reference to the genomic fragments identified by the cDNA.

In vivo phosphorylation of titin and nebulin in frog skeletal muscle

Titin and nebulin are two major protein components of the sarcomere matrix in striated muscles. Purified titin and nebulin from frog (Xenopus laevis) skeletal muscle are similar in size and in amino acid composition to their mammalian or avian counterparts. Both proteins contain substantial amounts of protein-bound phosphate: about 5 to 6 per titin subunit and 8 to 9 per nebulin subunit. Injection of radioactive inorganic phosphate into the dorsal lymph sacs of Xenopus laevis resulted in the significant incorporation of radioactivity into titin and nebulin within three days of incubation. Purified titin from in vivo labeled frog gastrocnemius muscle contains one mole of radioactive phosphoserine per mole of titin subunit. These data indicate that phosphorylation of frog titin and nebulin occurs in vivo.

[Hemihepatectomy under hepato-portal interruption at normal temperature for liver malignancies--a report of 20 patients]

From July 1984 to December 1985, hemihepatectomy was done in 20 liver cancer patients under normothermic interruption of porta hepatis. There were 19 primary and 1 secondary liver carcinomas. Of the former, 17 (89%) were associated with mild or moderate cirrhosis. The peak age ranged 36-60 years. Right hemihepatectomy was performed in 18 and left hemihepatectomy in 2 with an operative mortality of 0%. Hepatic failure or secondary bleeding was not found. In the specimens resected, the largest weight was 2,500 gm. The normothermic interruption of porta hepatis usually lasted 15-25 minutes, a time long enough for hemihepatectomy. This procedure, being simple in manipulation and less detrimental to physiologic and biochemical balance in the human body, is relatively practical and beneficial to hepatectomy.

Adenovirus sequences required for replication in vivo

We have studied the in vivo replication properties of plasmids carrying deletion mutations within cloned adenovirus terminal sequences. Deletion mapping located the adenovirus DNA replication origin entirely within the first 67 bp of the adenovirus inverted terminal repeat. This region could be further subdivided into two functional domains: a minimal replication origin and an adjacent auxillary region which boosted the efficiency of replication by more than 100-fold. The minimal origin occupies the first 18 to 21 bp and includes sequences conserved between all adenovirus serotypes. The adjacent auxillary region extends past nucleotide 36 but not past nucleotide 67 and contains the binding site for nuclear factor I.

Retinal detachment associated with coloboma of the choroid

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Effect of human tumor antigens on the active E-rosette-forming test (ARFT): a new diagnostic method for cancer

The "active" T-cell test was adapted into an in vitro assay for response to human tumor antigens, especially gastric, lung, liver, esophageal, and colonic tumors. Peripheral blood lymphocytes were isolated from 229 cancer patients, 60 non-cancer patients, and 70 normal adults. Tumor antigen, incubated with lymphocytes from patients with the corresponding cancer, produced a significant increase in the ability of the lymphocytes to function as active rosette-forming cells (ARFC) when compared with lymphocytes cultured without antigen (P less than 0.001). This potentiating effect on ARFC remained unimpaired even after tumor antigen refrigeration. Tumor antigen incubated with lymphocytes from normal donors produced no increase in ARFC ability. This assay appears to be specific for the antigen corresponding to the cancer of the given patient; for example, gastric tumor antigen increased the ARFC of gastric cancer patients, but produced no increase in ARFC of breast cancer patients. No interference by the HLA complex was found in this assay. This technique provides a novel in vitro method for investigating cell-mediated immunity and also a new, specific method for cancer diagnosis.

Right 25 bp terminus sequence of the nopaline T-DNA is essential for and determines direction of DNA transfer from agrobacterium to the plant genome

We have determined which sequences at the right border of the T-DNA region of the nopaline C58 Ti plasmid are required for transfer and/or integration of the T-DNA into the plant cell genome. The results indicate that the 25 bp T-DNA terminus repeat sequence, TGACAGGATATATTGGCGGGTAAAC, is directly responsible for T-DNA transfer; furthermore, this sequence is directional in its mode of action. A transfer-negative nononcogenic Ti plasmid derivative, pGV3852, was constructed, in which 3 kb covering the right T-DNA border region was substituted for by pBR322 sequences. The pBR322 sequences in pGV3852 provide a site for homologous recombination with pBR-derived plasmids containing sequences to assay for transfer activity. First, a 3.3 kb restriction fragment overlapping the deleted region in pGV3852 was shown to restore transfer activity. Second, a sequence of only 25 bp, the T-DNA terminus sequence, was shown to be sufficient to restore normal transfer activity. The transfer-promoting sequences are most active when reinserted in one orientation, that normally found in the Ti plasmid.

Titin is an extraordinarily long, flexible, and slender myofibrillar protein

" Titin " is a term used to describe a pair of closely related megadalton polypeptides that together are the third most abundant myofibrillar protein in a wide range of striated muscles. It has been proposed that titin and another giant protein, nebulin , are the major components of an elastic cytoskeletal lattice within the sarcomere. We have now purified the leading band, titin -2 (T2), of the titin doublet in native forms by extraction with Guba -Straub solution followed by chromatography. Electron microscopy of low-angle-shadowed and negatively stained specimens revealed that T2 chains self-assembled into extremely long (from 0.1 micron to over 1.0 micron), flexible, and extensible slender strands (4-5 nm in diameter) with axial periodicity. Furthermore, these strands tended to associate to form filamentous bundles and meshworks. Thus, titin appears to be ideally suited as a component of an elastic lattice that serves as an organizing scaffold or template for thick and thin filaments.

Cytoskeletal Matrix in Striated Muscle: The Role of Titin, Nebulin and Intermediate Filaments

In this chapter, first I will briefly describe the molecular properties of titin and nebulin --two extremely large, myofibrillar proteins--and discuss their distribution and organization in the sarcomere. Although these novel proteins are major myofibrillar components of a wide range of striated muscles, they have escaped the attention of muscle biochemists until very recently. As I shall point out below, biochemical studies of these proteins have been unexpectedly challenging; many standard techniques had to be modified before they became capable of handling such giant proteins. In addition, our structural studies of these proteins have encountered a challange of a different nature: how to explain their distribution in the sarcomere according to the currently accepted two filament sarcomere model, because these proteins do not appear to be thick or thin filament-associated regulatory or anchoring proteins. These studies have led us to reexamine the question of whether continuous, longitudinal filaments exist within the sarcomere of striated muscle. I will attempt to integrate our results, as well as available literature data, within the framework of a hypothetical sarcomere model which incorporates an elastic filamentous matrix consisting of titin and nebulin as additional sarcomere constituents. Finally, I will very briefly mention our recent findings that an extensive three dimensional network of intermediate (10 nm) filaments, distinct from titin and nebulin , is intimately associated with the sarcomere of adult striated muscle. I believe that the recognition of the existence of two sets of sarcomere-associated cytoskeletal filaments within adult striated muscle fibers may be a significant step toward resolving some of the unsettled questions in muscle mechanics such as those that have been discussed in this meeting.

A network of transverse and longitudinal intermediate filaments is associated with sarcomeres of adult vertebrate skeletal muscle

An extensive network of transverse and longitudinal filamentous bridges was revealed when small myofibril bundles, prepared from Triton-EGTA-treated rabbit skeletal muscles, were extracted with Kl to remove the majority of thin and thick filaments. Transmission and scanning electron microscopic studies of these salt-resistant cytoskeletal residues indicated (a) small bundles of short transverse filaments connect adjacent myofibrils by forming Z to Z and M to M bridges; (b) parallel, continuous longitudinal filaments connect the peripheries of successive Z-disks and ensheath the sarcomere. These transverse and longitudinal filaments have the characteristic morphology of intermediate filaments; (c) two rings of tightly interwoven and tangled filaments, connected laterally by short filaments, encircle each Z disk. This double-ring also encircles a weblike meshwork which penetrates the sarcomeric space. From the peripheries of these rings, transverse and longitudinal intermediate filaments emerge; and (d) a massive amount of material translocated and accumulated near Z disks during Kl extraction. The residues were fairly resistant to solubilization by urea and SDS, and complete dissolution was achieved only with guanidinium chloride. SDS PAGE indicated that the residues consisted mainly of titin, nebulin, and variable amounts of residual myosin and actin. Desmin represented only a few percent of total residual proteins; however, it may be a major component of the intermediate filament network. We suggest that the intermediate filament should be considered an integral sarcomeric component that may play important cytoskeletal roles in muscle structure and mechanics.

Purification and properties of human platelet P235. A high molecular weight protein substrate of endogenous calcium-activated protease(s)

Two major high molecular weight proteins of human platelets are highly susceptible to proteolytic degradation by endogenous calcium-activated protease activities. Of the two proteins, one has been identified as filamin (Mr = 250,000 subunit); the second, a Mr = 235,000 subunit protein contributing 3-8% of the total platelet proteins, has not been previously characterized. We have now purified this protein, designated P235, to apparent homogeneity (greater than 95%). P235 was extracted by a Triton X-100 and EDTA containing buffer at pH 9.0 and purified by a series of DEAE-cellulose, phosphocellulose, and gel filtration chromatographies. Purified P235 is a dimer of Mr = 235,000 subunit. Its Stokes radius (67 A) and frictional ratio of 1.3 suggest that P235 is approximately globular. Despite this similarity in subunit and molecular weight of P235 to filamin, spectrin, fibronectin, and myosin, its amino acid composition, immunological properties, and peptide map are distinctly different and showed no precursor-product relationship to these proteins. Calcium-activated protease(s) in crude platelet extract rapidly degrade P235 into a Mr = 200,000 stable fragment. Upon prolonged storage at 4 degrees C, purified P235 partially degrades into a Mr = 220,000 and a Mr = 200,000 fragment. This degradation pattern suggests that P235 contains a large Mr = 200,000 protease-resistant domain. The availability of pure P235 will be useful in elucidating the functional role of this platelet protein, as well as the role of calcium-activated proteases in platelet function.

Identification of an N2 line protein of striated muscle

Three unusually large myofibrillar proteins (Mr, > 500,000) are present in major amounts in the striated muscle of various species. the molecular properties and localization of two of these proteins (Mr, approximately 1 X 10(6)), named "titin," have been reported recently [Wang, K., McClure, J. & Tu, A.(1979) Proc. Natl. Acad. Sci. USA 76, 3698-3702]. We have now purified the third protein (Mr, approximately 5-6 X 10(5)), designated "band 3," from rabbit psoas myofibrils. Band 3 is distinct chemically and immunochemically from titin and myosin heavy chain. Immunofluorescent localization studies of band 3 in glycerinated rabbit psoas myofibrils indicated a biphasic distribution. In sarcomeres 1.8-3.7 micrometer long, band 3 is localized predominately on the N2 line in the phase-contrast lucent region of the I band. Quantitative analysis of light micrographs confirmed the unique behavior of N2 lines described in early electron microscopic studies. As the sarcomeres lengthen, the N2 line moves away from both the Z line and the M line, maintaining the same proportional distance. In very short sarcomeres (1.5-1.8 micrometer), band 3 is found mainly in the A band, suggesting that either the N2 line moves into the A band or that band 3 has dissociated from the N2 line which remains near the Z line. We conclude that band 3 is an N2 line component of rabbit skeletal myofibrils.