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OBJECTIVES AND DESIGN: Actin is the dominating protein in mammalian cells, including muscle cells, and is released into the circulation after tissue injury. Gc-globulin, one of the proteins in the Extracellular Actin Scavenger System (EASS) is responsible for the clearance of actin from the circulation. Clinical studies show that plasma levels of Gc-globulin are reduced in situations with tissue death, and that the degree of reduction correlates with development of organ dysfunction and survival. The purpose of the present study was to describe the serial changes in Gc-globulin after a standardized surgical procedure resulting in major muscle injury, comparing changes in Gc-globulin with changes in other acute phase proteins. MATERIAL AND METHODS: Twelve patients who underwent posterolateral lumbar fusion from L4 or L5 to sacrum were included in the study. Peripheral venous blood samples were obtained before surgery and on day 1, 3, 5, 12, 21, and 28 after surgery. Serum samples were analyzed for total Gc-globulin (Gc(total)), percentage of Gc-globulin complexed with actin (GC(complexed)), albumin, orosomucoid, haptoglobin, transferrin and creatin phosphokinase (CK). RESULTS: Gc(total) decreased to 87% of pre-operative values on day one. Thereafter the levels increased to a maximum of 135% of pre-operative values on day five, approaching baseline values towards the end of the observation period. Compared to this, changes in GC(complexed) displayed a mirror-like time-course, with levels of Gc(total) and GC(complexed) being significantly inversely correlated on day one (P < 0.05). Levels of albumin remained below pre-operative values the first three weeks post-operatively, reaching baseline at the end of the observation period (P < 0.05). CONCLUSION: The initial changes in Gc-globulin can be explained by increased release of actin from injured muscle tissue. Subsequently Gc-globulin displays characteristics of a so-called positive acute phase reactant, supporting previous in vitro studies, and clinical studies after minor surgery. In spite of genetic linkage and structural homology Gc-globulin and albumin are regulated differently after surgical trauma.

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Insulin-like growth factor-(IGF) II and IGF-I and IGF-II/mannose 6-phosphate receptors were expressed in a thoracopulmonary malignant small round cell tumor (MSRCT) from a 14-year-old boy. Northern analysis showed that the MSRCT expresses multiple IGF-II mRNA of 6.0, 4.8, 4.2, and 2.2 kilobase from promoters P3 and P4 of the human IGF-II gene. Chromatography and radioimmunoassay revealed two forms of IGF-II with molecular masses of 7.5 kilodalton (kDa) and 10 kDa, corresponding to mature IGF-II and IGF-II with a C-terminal extension, in concentrations of 61 and 41 ng/g/tumor tissue, respectively. By a combined reverse transcription-polymerase chain reaction analysis, the authors also show that the MSRCT expresses IGF-I and IGF-II/mannose 6-phosphate receptor mRNA. The plasma concentration of IGF-II was 600 ng/ml and within the normal range of serum IGF-II. IGF binding proteins (IGFBP) of 41.5, 38.5, 34, 30, and 24 kDa were present in serum. Compared with normal plasma from healthy subjects and an age-matched group of boys, the level of the 41.5, 38.5, and 30 kDa IGFBP were approximately 3-fold elevated. The authors conclude that transcription of the IGF-II gene leads to the production of significant amounts of 10 kDa IGF-II and 7.5 kDa IGF-II. IGF-II may stimulate the proliferation of MSRCT by interaction with IGF-I receptors on the cells.

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D2 is a nervous-specific membrane protein enriched in fractions of synaptosomal membranes from rat brain. Recently, an immunochemical relationship between D2 and the chick cell adhesion molecule (CAM) has been demonstrated. There is reason to believe that D2 is involved in adhesion phenomena between neurites. The purpose of the present study was to purify and further characterize the D2 protein from rat brain. In the developed purification procedure synaptosomal membranes from rat brains were prepared and solubilized by means of non-ionic detergent. The subsequent purification steps were hydroxylapatite chromatography, wheat germ lectin affinity chromatography, gel filtration, and lysine affinity chromatography. The purified D2 was found to be enriched 240 times compared with the starting brain homogenate and 120 times compared with the synaptosomal membrane fraction. The recovery of D2 was 26% when the amount of D2 in the synaptosomal membrane fraction was set to 100%. The purified D2 antigen was used for production of monospecific rabbit antisera, and it was found to be composed of two polypeptides of apparent molecular weights 130,000 and 150,000, respectively.

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In a new procedure, rocket immunoelectrophoresis is performed at pH 8.7 with rabbit antibodies and 5% polyethyleneglycol 6000 in the agarose gel. After the pH in the gel has been changed to 5 the nonprecipitated immunoglobulins are electrophorsed out of the gel simultaneously with the electrophoresis of 125I-labeled swine antibodies against rabbit IgG into the gel. The latter antibodies tag the rabbit IgG, which is not present only in the precipitates. The radioactive precipitates are visualized by autoradiography. The method permits quantification of antigens down to an amount of approximately 0.5 ng; well-defined rockets are not formed below this limit. Compared to conventional protein staining with Coomassie brilliant blue, this represents an increase in sensitivity of up to 20 times.

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