Immunolocalization of AMP-deaminase isozymes in human skeletal muscle and cultured muscle cells: concentration of isoform M at the neuromuscular junction.

Abstract

The three major isoforms of AMPdeaminase ( M a ) were localized in human skeletal m d e and cultured muscle cells by immunocytochemistry. The M isoform was mainly located in Type II muscle fibers and showed a clear cross-striation.Particularly strong staining was present at the neuromuscular junction. Capillaries were also immunoreactive. The L koform was predomhmtly observed in nerve bundles and to a minor extent in smooth muscle cells and endothelial cells. The E isoform was predominantly present in smooth muscle cells, and to a lesser extent in Type I muscle fibers and nerve bundles. In quadriceps musde of patients with myoadenylate deaminase deficienq, no immMOst?ining for eroduction Adenosine monophosphate deaminase (AMPda; EC 3.5.4.6.) catalyzes the irreversible hydrolytic deamination of AMP to IMP and ammonia. AMPda plays a role in purine nucleotide interconversion and is one of the three enzymes involved in the purine nudeotide cycle (Van den Berghe et al., 1992; Tullson and Terjung, 1991; henstein, 1972, 1990.In muscle, this cycle is involved in (a) the maintenance of the high ATPADP ratio by pulling the myokinase reaction (2 ADP ATP + AMP) towards ATP by AMP removal, (b) limiting the degradation of adenine nucleotides to purine bases, (c) replenishment of citric acid cycle intermediates leading to an enhancement of aerobic energy production, and (d) deamination of amino acids for oxidative metabolism. Two other proposed functions, regulation of phosphofructokinase activity by NH4' concentration and regulation of phosphorylase b activity by the IMP concentration, are less likely (Van den Berghe et al., 1992; Tullson and Terjung, 1991).In human, at least four isofonns of the tetrameric AMPda exist:Correspondence ta T. the M (muscle), the L (liver), and the El and E2 (erythrocyte) isoforrns (Ogasawara et al., 1982). The M, L, and E isoforms differ from each other in kinetic, regulatory, immunological, and chromatographic properties (Ogasawara et al., 1982). In rat these isozymes are named A, B, and C isoforms, respectively (Thompson et al., 1992).AMPda is a multigene family (Morisaki et al., 1990). The M isoform, the predominant form in skeletal muscle, is encoded by the AMPDl gene , the L isoform by the AMPD2 gene (Bausch-Jurken et al., 1992) and the El and E2 isoforms, presumably through altemative splicing, by the AMPD3 gene (Mahnke-Zizelman and Sabina, 1992). Altemative splicing in the AMPDl and AMPD2 genes predicts multiple forms for the M and L isoforms as well (Morisaki et al., 1993;Van den Bergh and Sabina, 1993).Biochemical analysis of AMPda isoforms indicates a restricted distribution in human tissues (Ogasawara et al., 1982). Recently, the distribution of the major isoforms of AMPda has been documented for rat skeletal muscle (Thompson et al., 1992). We report here on the disuibution of AMPda isofonns in human skeletal muscle and cultured muscle cells. We found a salient occurrence of the M isoform in the postsynaptic part of the neuromuscular junction. Materials and MethodsSkeletal Muscle ...

Novel Aspects of Tetramer Assembly and N-terminal Domain Structure and Function Are Revealed by Recombinant Expression of Human AMP Deaminase Isoforms

“…Clinical divergence in CHF is presumably related to different rates of cardiac adenosine production in these two groups of individuals (38). AMPD3 is expressed in type I skeletal muscle fibers (7,39) and in the heart (7), thus creating a potential for assembly of hybrid tetrameric enzymes in these two tissues. Production of AMPD1/AMPD3 enzymes in type I skeletal muscle fibers of individuals with inherited AMPD1 deficiency and in CHF patients would serve to maximize AMPD1 expression and may influence clinical outcomes related to this genetic defect.…”

Presence in Human Skeletal Muscle of an AMP Deaminase-associated Protein That Reacts with an Antibody to Human Plasma Histidine-Proline-rich Glycoprotein

“…Together, these observations suggest that the different responses to the AMPD staining among the IIA fibers of different specimens can be ascribed to different levels of an AMPD isoform not related to the HPRG-like protein. At least two AMPD isoenzymes differing in regulatory properties and localization have been identified in various skeletal muscle fibers (Raggi et al 1975;Van Kuppevelt et al 1994) and a 4-10-fold higher level of AMPD in white muscle than in red muscle has been documented in different species (Raggi et al 1969). By chromatography on cellulose phosphate of extracts of rabbit red muscles, two peaks of AMPD activity were obtained (forms A and B), the second having the same chromatographic properties as the single form present in white muscles (Raggi et al 1975).…”

N-terminal Sequence and Distal Histidine Residues Are Responsible for pH-regulated Cytoplasmic Membrane Binding of Human AMP Deaminase Isoform E

“…AMPD1 levels are high in all fibers but more so in glycolytic muscle, whereas AMPD3 is primarily restricted to oxidative fibers (24,49,50). The AMPD1 isoform exhibits a high contractile protein binding capacity that is, in part, attributable to N-terminal sequence (20,21).…”

“…This observation is functionally significant because contractile protein binding is an important physiological regulator of catalytic activity in stimulated skeletal muscle (22,23), the primary site of AMPD1 expression. Although more widely distributed across human tissues and cells (15), the highest level of AMPD3 expression is also observed in skeletal muscle (3), where isoform E appears confined predominantly to type I fibers (24). However, up to 48 amino acids in the unique N terminus of isoform E dramatically suppress contractile protein binding capacity of this enzyme (21), a behavior that could facilitate other intracellular interactions.…”