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Creatine kinase isoenzymes (CK = ATP: creatine N-phosphoryl transferase, EC 2.7.3.2) were localized in situ in cryosections of intact sarcomeric muscle by immunocytochemical staining. Similar to cardiac muscle, spermatozoa and photoreceptor cells, mitochondrial-type CK (Mi-CK) localization in skeletal muscle was also restricted to mitochondria. Besides the well-documented localization of muscle-type (M-CK) at the M-line and at the sarcoplasmic reticulum, surprisingly, most of the sarcoplasmic M-CK was also highly compartmentalized and was mainly confined to the I-band. The localization of M-CK at the I-band coincided with that of adenylate kinase and aldolase. In intact muscle, the diffusion equilibrium decisively favours occupancy by all three enzymes of the I-band, with the acto-myosin overlap region of the A-band acting as a molecular sieve, excluding to a large extent all three enzymes from the acto-myosin overlap region. This indicates that in intact muscle, this region of the A-band may be less accessible in vivo to soluble, sarcoplasmic enzymes than thought before. If muscle were permeabilized by chemical skinning before fixation, I-band CK, as well as aldolase and adenylate kinase, were solubilized and disappeared from the myofibrils, but the fraction of M-CK which was specifically associated with the M-line remained bound to the myofibrils. Implications of these findings are discussed with respect to the functional coupling of I-band-CK with glycolysis, to the formation of large multienzyme complexes of glycolytic enzymes with CK and to the supply of energy for muscle contraction in general.

Two isoforms of creatine kinase (CK; ATP:creatine N-phosphotransferase, E.C. 2.7.3.2), brain type (BB-CK) and mitochondrial type (MiMi-CK), but not the muscle types (MM-or hybrid MB-CK), were identified by cellulose polyacetate electrophoresis and immunoblots in retina from adult chickens. Indirect immunofluorescence labeling of cryosections of retinas revealed high concentrations of BB-CK in both rod and cone photoreceptor cells. Most of the fluorescence staining with anti-B-CK antibodies was found within the myoid and the ellipsoid portions of inner segments and the peripheral region of the outer segments. Significant staining with anti-B-CK antibodies was also found in horizontal cells and in the optical nerve fibers, with additional stratified staining in the inner plexiform layer. MiMi-CK was solely demonstrated in the ellipsoid portion of the photoreceptor cells. The presence of high concentrations of compartmentalized CK isoenzymes within photoreceptor cells (%3O enzyme units/mg) as well as the relatively high concentration of total creatine in these cells (-1-15 mM) indicates an important physiological function for CK and phosphocreatine in the energy transduction of vision.In skeletal and heart muscle, some of the creatine kinase (CK; ATP:creatine N-phosphotransferase, EC 2.7.3.2) has been found to be localized in an isoenzyme-specific way at different subcellular structures or in different compartments-e.g., in the myofibrillar M-band, on the sarcoplasmic reticulum, on the plasma membrane, and within the mitochondria (for review, see refs. 1-3). It is thought that at these different locations, CK represents an ATP-regenerating system functionally coupled to microcompartments that require high local ATP/ADP ratios and immediate replenishment and supply of ATP-e.g., the actin-activated Mg2+-ATPase of myosin, the sarcoplasmic Ca2+-ATPase, or the sarcolemmal Na+/K +-ATPase, all being sites of high energy consumption. The soluble part of the muscle isozyme (MM-CK) and of the mitochondrial isoform (MiMi-CK) are thought to be functionally coupled to the ATP-producing systems of glycolysis and oxidative phosphorylation, respectively (3). The microcompartmentation of CK at these sites allows rapid transfer of metabolically active ATP into phosphocreatine, which represents a storage as well as a transport form of energy-rich phosphate. Thus, the sites of high energy requirement and energy production are thought to communicate by a phosphocreatine-shuttle (1-5)-a model that has gained increasing support also by recent experiments using novel phosphorus NMR techniques with high resolution at a faster time scale (6). In order to find out whether the phosphocreatine shuttle is a general metabolic feature of tissues with immediate high energy requirements, as has been postulated for muscle (7), electric organ of Torpedo marmorata (8), and sperm cells from sea urchin (9), chicken, and man (10), we studied the distribution of CK in chicken retina. A study by Dontsov et al. (11) indicated the presence of CK acti...

Two isoforms of creatine kinase (CK, E.C. 2.7.3.2), the brain type BB-CK and the mitochondrial-bound MiMi-CK, as well as adenylate kinase (myokinase, E.C. 2.7.4.3) were identified in washed spermatozoa from chicken and man by cellulose polyacetate electrophoresis and immunoblots. BB-CK was localized by indirect immunofluorescence staining within the sperm tail but not in the head portion. MiMi-CK is confined to the midpiece region rich in mitochondria and has been localized directly by immunogold staining within the mitochondria. In contrast to chicken, seminal plasma from man was also found to contain considerable amounts of BB-CK. Total creatine content of spermatozoa (8-15 mM) and seminal plasma (3.8 +/- 0.4 mM) as well as preliminary experiments with metabolic blockers indicate a dependence of sperm motility on CK and phosphoryl creatine (CP). The presence of two CK isoforms located in different 'compartments' of spermatozoa suggests a CP-shuttle in sperm similar to that described for cross-striated muscle.

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