Effects of cardiac myosin binding protein-C on the regulation of interaction of cardiac myosin with thin filament in an in vitro motility assay

Modulatory role of whole cardiac myosin binding protein-C (сMyBP-C) in regulation of cardiac muscle contractility was studied in the in vitro motility assay with rabbit cardiac myosin as a motor protein. The effects of cMyBP-C on the interaction of cardiac myosin with regulated thin filament were tested in both in vitro motility and ATPase assays. We demonstrate that the addition of cMyBP-C increases calcium regulated Mg-ATPase activity of cardiac myosin at submaximal calcium. The Hill coefficient for ‘pCa-velocity’ relation in the in vitro motility assay decreased and the calcium sensitivity increased when сMyBP-C was added. Results of our experiments testifies in favor of the hypothesis that сMyBP-C slows down cross-bridge kinetics when binding to actin.     

Evidence against essential roles for subdomain 1 of actin in actomyosin sliding movements

We have engineered acto-S1chimera proteins carrying the entire actin inserted in loop 2 of the motor domain of Dictyostelium myosin II with 24 or 18 residue-linkers (CP24 and CP18, respectively). These proteins were capable of self-polymerization as well as copolymerization with skeletal actin and exhibited rigor-like structures. The MgATPase rate of CP24-skeletal actin copolymer was 1.06 s(-1), which is slightly less than the V(max) of Dictyostelium S1. Homopolymer filaments of skeletal actin, CP24, and CP18 moved at 4.7+/-0.6, 2.9+/-0.6, and 4.1+/-0.8 microm/s (mean+/-SD), respectively, on coverslips coated with skeletal myosin at 27 degrees C. Statistically thermodynamic considerations suggest that the S1 portion of chimera protein mostly resides on subdomain 1 (SD-1) of the actin portion even in the presence of ATP. This and the fact that filaments of CP18 with shorter linkers moved faster than CP24 filaments suggest that SD-1 might not be as essential as conventionally presumed for actomyosin sliding interactions.     

Evidence for actin transformation during the contraction-relaxation cycle of cytoplasmic actomyosin: Cycle blockade by Phalloidin injection

1) The injection of a mushroom drug, Phalloidin (750 microgram -1 mg/ml), into the endoplasmic channel of Physarum veins induces an irreversible blockade of the intrinsic contraction-relaxation automaticity of the ectoplasmic tube wall, as measured by tensiometrical methods. 2) The morphological responses to Phalloidin injection include an increase and condensation of cytoplasmic actomyosin sheets bordering the plasmalemma invaginations within the ectoplasmic tube and a more pronounced dense layer of "groundplasm" in the cell cortex. This is in accordance with experiments with other cells as well as with Physarum. 3) The addition of marker particles to the injection solution revealed that the injected substances can be brought into direct contact with the contractile substrate, before newly formed membranes separate off the injection fluid. 4) Since Phalloidin irreversibly transforms oligomeric actin into a filamentous "Phalloidin-actin complex" and because this transformation does not hinder the actin in activating myosin ATPase, it is concluded that the contraction-relaxation cycle of cytoplasmic actomyosin in Physarum involves actin transformations. If these transformations are hindered, e.g. by Phalloidin, one stage and thereby the whole cycle is sustained which results in a blockade of the intrinsic contraction automaticity. 5) The functional importance of actin transformations in the congraction physiology of cytoplasmic actomyosins and cell motility phenomena is discussed.     

肌球蛋白轻链激酶非激酶活性调节磷酸化肌球蛋白ATP酶活性及肌丝运动

肌球蛋白轻链激酶(myosin light chain kinase,MLCK)具有激酶和非激酶活性,在平滑肌收缩过程中起着关键酶调控的作用.为进一步阐明MLCK非激酶活性在平滑肌收缩过程中的调节作用,利用已删除部分激酶区域的MLCK重组体(pGEXF6.5)在大肠杆菌中进行表达,采用亲和层析技术纯化表达的MLCK片段,应用EnzChek磷分析试剂盒检测MLCK片段对磷酸化肌球蛋白、水解重酶解肌球蛋白(heavymeromyosin,HMM)及肌球蛋白亚片段1(subfragmentl,S1)ATP酶活性的影响,体外检测MLCK片段对肌动蛋白肌丝运动的调节.研究结果显示,pGEX-F6.5重组表达载体在大肠杆菌中以可溶性GST融合蛋白的形式表达.该融合蛋白经Glutathione-Sepharose4B纯化、SDS-PAGE鉴定得到较纯的单一表达条带.纯化的MLCK片段对磷酸化肌球蛋白、HMM和S1的ATP酶活性均有明显激活作用.MLCK片段激活磷酸化肌球蛋白ATP酶活性为:Vmax=(19.426±1.669)倍;Km=(0.486±0.106)μmol/L,MLCK片段对磷酸化HMM和S1的ATP酶活性也有相似的刺激作用.体外肌丝运动研究表明,随着MLCK片段浓度的增加,磷酸化肌球蛋白与肌动蛋白结合的数量不断增加,肌丝运动的速度也随之增加.上述结果表明,MLCK的C端非激酶活性具有调节磷酸化的肌球蛋白ATP酶活性及肌丝运动的作用.     

In vitro translation of maize ADH: Evidence for the anaerobic induction of mRNA

Total cellular RNA from anaerobically stressed maize seedling roots was used to stimulate in vitro translation of authentic maize alcohol dehydrogenase (ADH) in a rabbit reticulocyte lysate system. Total products from such reactions were displayed on NEPHGE-SDS two-dimensional gels and the Adhl-specific translation products were identified by using RNA from sib seedlings segregating for Adhl charge and size variants. The application of a rapid RNA isolation procedure allowed the efficient isolation of biologically active RNAs from small amounts of seedling material. Maize ADHs translated in vitro are identical in size to in vivo ADH. Further, no ADH was detected in the products of an in vitro translation reaction stimulated by total RNA from aerobically grown seedlings. This suggests that induction of ADH protein by anaerobic stress is accomplished by production of Adh mRNA rather than activation of sequestered mRNA. The mRNAs for maize ADH1 and ADH2 are among a small class of mRNAs induced during anaerobiosis.Research was supported by NSF Grant PCM 76-11009. M.D.B. is supported by National Institute of Health Grant PHS 5 T32 GM07227-04. R.J.F. is a Predoctoral Trainee in Genetics supported by National Institute of Health Training Grants 82 and 7757 from the National Institute of General Medical Sciences.     

Use of an isolated guinea-pig ileum assay to detect bioactive compounds in microalgal cultures

An isolated guinea-pig ileum preparation was used to screen for bioactive compounds from algae. 212 culture supernatants and methanolic extracts of randomly chosen marine and freshwater algae were tested for their effect on electrically evoked muscle contractions (recorded as a change in tension) and on the resting muscle tone. 15 out of 42 (35%) of the marine algae tested and 5 out of 64 (8%) of freshwater algae gave positive results. Of the 20 algae giving positive results, 6 had previously been shown to produce bioactive compounds (mainly toxins) but we can find no reports in the literature of bioactive compounds from the remaining 14. Of these 14 cultures, 9 were axenic and therefore production of the biological activity can be assigned unambiguously to the alga. These results confirm the usefulness of the guinea-pig ileum preparation as a screen for bioactive compounds from microbial cultures.     

The B2 alternatively spliced isoform of nonmuscle myosin II-B lacks actin-activated MgATPase activity and in vitro motility

We report the initial biochemical characterization of an alternatively spliced isoform of nonmuscle heavy meromyosin (HMM) II-B2 and compare it with HMM II-B0, the nonspliced isoform. HMM II-B2 is the HMM derivative of an alternatively spliced isoform of endogenous nonmuscle myosin (NM) II-B, which has 21-amino acids inserted into loop 2, near the actin-binding region. NM II-B2 is expressed in the Purkinje cells of the cerebellum as well as in other neuronal cells [X. Ma, S. Kawamoto, J. Uribe, R.S. Adelstein, Function of the neuron-specific alternatively spliced isoforms of nonmuscle myosin II-B during mouse brain development, Mol. Biol. Cell 15 (2006) 2138-2149]. In contrast to any of the previously described isoforms of NM II (II-A, II-B0, II-B1, II-C0 and II-C1) or to smooth muscle myosin, the actin-activated MgATPase activity of HMM II-B2 is not significantly increased from a low, basal level by phosphorylation of the 20 kDa myosin light chain (MLC-20). Moreover, although HMM II-B2 can bind to actin in the absence of ATP and is released in its presence, it cannot propel actin in the sliding actin filament assay following MLC-20 phosphorylation. Unlike HMM II-B2, the actin-activated MgATPase activity of a chimeric HMM with the 21-amino acid II-B2 sequence inserted into the homologous location in the heavy chain of HMM II-C is increased following MLC-20 phosphorylation. This indicates that the effect of the II-B2 insert is myosin heavy chain specific.     

Cryopreservation of isolated micropores of spring rapeseed (Brassica napus L.) for in vitro embryo production

Microspore cryopreservation is a potentially powerful method for long-term storage of germplasm for in vitro embryo production in plant species. In this study, several factors influencing embryo production following the ultra-low temperature (–196 °C in liquid nitrogen) storage of isolated microspores of rapeseed (Brassica napus L.) were investigated. Microspores were prepared in cryogenic vials and subjected to various cooling treatments before immersion in liquid nitrogen for varying periods. Efficiency of microspore cryopreservation was reflected by in vitro embryo production from frozen microspores. Of all the cooling treatments, microspores treated with a cooling rate of 0.25% °C/min and a cooling terminal temperature of –35 °C before immersion in liquid nitrogen produced the highest embryo yields (18% and 40% of unfrozen controls in two genotypes, respectively). Fast thawing in a 35 °C water bath was necessary to recover a high number of embryos from microspore samples being frozen at a higher cooling rate, while thawing speed did not affect samples after freezing at a slower cooling rate. The storage density of cryopreserved microspores affected embryo production. Storage at the normal culture density (8×10⁴ microspores/ml) was less efficient for embryo production than at high densities (4×10⁶ microspores/ml and 1.6×10⁷ microspores/ml), although no significant difference was found between the high densities. Evaluation of plant lines derived from frozen microspores indicated no variation in isozyme pattern and no enhanced cold tolerance of these lines. Isolated microspores of B. napus could be stored for extended period for in vitro embryo production.     

Evaluation of the physiological value of porcine luteal cells isolated in various stages of the luteal phase: Tissue culture approach

Porcine luteal cells were collected from corpora lutea in four different stages of the luteal phase and cultured as monolayers. Progesterone (P₄) secretion was assayed using radioimmunoassays (Gregoraszczuk, 1991). Luteal cells cultured from porcine corpora lutea collected in the early luteal phase maintained steroidogenic capacity for 6 days in culture until the time comparable with midluteal corpora lutea. Luteal cells collected from mature and regressing corpora lutea did not dedifferentiate during 2 days of culture. After this time secretion of progesterone decreased to undetectable amounts characteristic of old corpora lutea. The regression in the culture progressed. The results demonstrate that the degree of the decline of progesterone depends on the type of corpus luteum, which is connected to particular time intervals of the luteal phase. Before starting experiments it is necessary to take into consideration the stage of the luteal phase from which the material is collected for culture. This study provides evidence that long term culture is useful for investigating a variety of aspects of luteal function only if cells are collected in the early luteal phase. Short term culture is suitable for investigation of cells collected from mid and late luteal phase. Regulation of luteal function is dependent on stage of the luteal phase.     

Evidence for an interaction effect during <Emphasis Type="Italic">in vitro</Emphasis> rooting of oil palm (<Emphasis Type="Italic">Elaeis guineensis</Emphasis> Jacq.) somatic embryo-derived plantlets

In vitro rooting of oil palm shoots derived from somatic embryos was achieved through a single-phase protocol in which three shoots are cultured in the same culture tube on an α-naphtaleacetic acid-enriched culture medium. Rooting performance was dependent on both the genetic origin and initial size of the shoot explants. All shoots from a given tube showed a tendency to give roots of the same type, independent of the original size of the explant. Whatever the clonal line, longer-size shoots (L-type: >9 cm) showed higher rooting rates than medium-size (M-type: 7–9 cm) and short-size ones (S-type: 5–7 cm). When groups of three shoots from the same clonal line were rooted together in the same culture tube, the combination of plant size within the group impacted overall quality of rooting. Within triplets of shoots containing more than one short individual, the probability of obtaining adequate rooting was low. Similarly, when more than one long shoot was included in the triplet rooting, quality was also poor. By avoiding such combinations, the rate of well-rooted plantlets increased by 25%, with a maximum of 66% when triplets of S/M/L combination were used. Smaller shoots, which usually showed poor rooting performance, were therefore found to benefit from the presence of their neighbors. This interaction between the sizes of individuals in a given tube was found to be associated with a within-tube correlation effect, a phenomenon previously described as “event coupling,” which was estimated using a distorted binomial-type distribution of probabilities. The resulting calculation of a coupling factor (average r = 0.60) explains the behavior of shoots within the same culture tube and their average rooting performance. Modeling of the interactions that occurred during in vitro rooting is described here and is recommended for improvement of this critical step in micropropagation.     

Polyamine patterns in iron- and sulphur-oxidizing bacteria isolated from an Indian copper mine indicate requirement of spermidine for growth under acid conditions

Spermidine was found to be the predominant polyamine in all the acidophilic as well as neutrophilic strains of chemolithotrophic iron- and sulphur-oxidizing bacteria and associated organotrophic cultures inhabiting a copper mining ecosystem. Adaptation of neutrophilic Thiobacillus thioparus strain to pH 5.0 was found to increase the spermidine content of the cells 2.3 times while the biomass yield decreased by 50%. However, exogenous supplementation of spermidine could restore the biomass yield to levels obtainable at pH 7.0. These observations indicate that spermidine plays a significant role in adaptive behaviour of microorganisms in natural ecosystems, especially under acid conditions. This revised version was published online in July 2006 with corrections to the Cover Date.     

利用微嫁接技术促进麻疯树再生不定芽的生长

该研究以麻疯树种子实生苗的小芽和芽条为接穗,以带有胚根的实生苗下胚轴为砧木进行无菌微嫁接,试图建立新的有效微嫁接方法,解决农杆菌介导的麻疯树遗传转化体系中再生的转化不定芽难以顺利发育成完整植株的问题。结果表明:(1)抗生素对嫁接苗的生长有显著的抑制作用。(2)进行微嫁接所用砧木的苗龄以5d为宜。(3)进行微嫁接时适宜采用的砧木类型为带有部分胚根的下胚轴。(4)嫁接苗在0.3mg/L IBA+2mg/L谷氨酰胺+1/2MS培养基上的生长效果最好。(5)嫁接苗的移栽成活率最高可达76.40%。(6)以小芽或芽条为接穗的嫁接苗均可正常生长。该研究建立的麻疯树微嫁接体系,为解决麻疯树转化不定芽或芽条生长发育困难的问题提供了一条新的途径。     

Evidence for an involvement of glutamine synthetase in regulation of nitrogenase activity in Rhodopseudomonas capsulata

In the presnet studies with whole cells and extracts of the photosynthetic bacterium Rhodopseudomonas capsulata the rapid inhibition of nitrogenase dependent activities (i.e. N₂-fixation acetylene reduction, or photoproduction of H₂) by ammonia was investigated. The results suggest, that the regulation of the nitrogenase activity by NH ₄ ⁺ in R. capsulata is mediated by glutamine synthetase (GS). (i) The glutamate analogue methionine sulfoximine (MSX) inhibited GS in situ and in vitro, and simultaneously prevented nitrogenase activity in vivo. (ii) When added to growing cultures ammonia caused rapid adenylylation of GS whereas MSX abolished the activity of both the adenylylated and unadenylylated form of the enzyme. (iii) Recommencement of H₂ production due to an exhaustion of ammonia coincided with the deadenylylation of GS. (iv) In extracts, the nitrogenase was found to be inactive only when NH ₄ ⁺ or MSX were added to intact cells. Subsequently the cells had to be treated with cetyltrimethylammonium bromide (CTAB). (v) In extracts the nitrogenase activity declined linearily with an increase of the ration of adenylylated vs. deadenylylated GS. A mechanism for inhibition of nitrogenase activity by ammonia and MSX is discussed.Abbreviations BSA bovin serum albumine - CTAB cetyltrimethylammonium bromide - GOGAT l-glutamine: 2-oxoglutarate amino transferase - GS glutamine synthetase - HEPES N-2-hydroxyethylpiperazine-N-2-ethane sulfonic acid - MSX l-methionine-d,l-sulfoximine     

Establishment of in vitro plants, cell and tissue cultures from Oldenlandia affinis for the production of cyclic peptides

In vitro cultured plants from Oldenlandia affinis were established from seeds and grown on a hormone-free medium. In vitro plants produced the cyclic peptide kalata B1 in concentrations of 0.67 mg g⁻¹ dry weight after growth of 30 days. This was approximately 50% of the concentration analysed in green house plants (shoot tips), where different concentrations have been determined in leaves (1.82 mg g⁻¹), shoot tips (1.36 mg g⁻¹), stems (0.36 mg g⁻¹), and in flowers (0.16 mg g⁻¹). Callus and cell suspension cultures could be initiated from aseptic root, stem and leaf explants of O. affinis seedlings and plants. Different light intensities were shown to affect culture growth as well as chlorophyll synthesis. The friable callus was then used for the establishment of a cell suspension culture. Fresh and dry weight measurements showed that growth was optimal on MS medium supplemented with 0.4 mg l⁻¹ 2,4-dichlorophenoxyacetic acid (2,4-d). Leaf suspensions cultured on this medium showed a 4-fold increase of biomass by the first week of incubation. No quantifiable amounts of kalata B1 were produced under these conditions. Morphological differentiation seems to be essential for cyclic peptide production. Therefore, several undifferentiated as well as organised cell lines of O. affinis have been developed. These cell lines will constitute a worthwhile starting point for the optimisation of kalata B1 synthesis in liquid media to the objective of producing cyclic peptides under controlled and defined conditions in bioreactors.     

Role of the host cell cycle in theAgrobacterium-mediated genetic transformation ofPetunia: Evidence of an S-phase control mechanism for T-DNA transfer

Chimeric -glucuronidase (GUS) gene expression in an efficientAgrobacterium-mediated transformation system utilising mesophyll cells ofPetunia hybrida synchronized with cell cycle phase-specific inhibitors (mimosine and colchicine) was used to show the absolute requirement of S-phase for transfer and/or integration of the transferred DNA (T-DNA). Flow-cytometric analysis of nuclear DNA content and immunohistological detection of bromodeoxyuridine (BrdUrd) incorporation showed that, prior to phytohormone treatment, most (98%) mesophyll cells were at GO-Gl-phase (quiescent phase) and no cell division was occurring. After 48 h and 72 h of phytohormone treatment, there was a rapid increase in S-G2-M-phase populations (> 75%) and a concomitant decrease (down to 24%) in G0–-G1-phase cells. Assays of GUS showed that maximum transformation (> 95% of explants) also occurred after this period. Our data showed that mimosine and colchicine blocked the mesophyll cells at late Gl-phase and M-phase, respectively. No transformation (= GUS expression) was observed in phytohormone-treated cells inhibited in late G1 by mimosine. However, after removal of mimosine, 82% of the explants were transformed, indicating the non-toxic and reversible effect of the inhibitor. On the other hand, a relatively high transformation frequency (65% of explants) was observed after blocking the cell cycle at M-phase with colchicine. However, only transient, but no stable, gene expression (= kanamycin-resistant callus formation) was observed in colchicine-treated M-phase-arrested cells. Similarly, endoreduplication of nuclear DNA, which occurred during the 48 h of phytohormone treatment in some mesophyll cells and cells located along the minor veins in the leaf explants, resulted in transient GUS expression only. These observations indicate a direct correlation between endoreduplication and transient GUS gene expression. Obviously, for stable GUS gene expression, cell division and proliferation are required, indicating that both DNA duplication (S-phase) and cell division (M-phase) are strongly related to stable transformation. We propose that the present system should facilitate further dissection of the process of T-DNA integration in the host genome and therefore should aid in developing new strategies for transformation of recalcitrant plants.Abbreviations BAP 6-benzylaminopurine - BM basal medium - BrdUrd bromodeoxyuridine - GUS -glucuronidase - Km^R kanamycin resistant - T-DNA transferred DNA     

Development of adventitious shoots from <Emphasis Type="Italic">in vitro</Emphasis> grown <Emphasis Type="Italic">Cydonia oblonga</Emphasis> leaves as influenced by different cytokinins and treatment duration

The effects of three cytokinins, kinetin 4.5 M (Kin), 6-benzylaminopurine 4.5 M (BA) and N-phenyl-N1,2,3- thiadiazol-5-yl-urea 4.5 M (TDZ), and the effects of different treatment duration on the regeneration of adventitious shoots from quince (Cydonia oblonga Mill.) leaves were studied. In a first experiment, leaves treated with Kin for 0, 8, 16 and 24 d were transferred to BA or TDZ-containing growth medium. In a second experiment TDZ applied for 0, 4, 8, 12, 16 and 24 d was followed by BA. All treatments included 0.5 M -naphthaleneacetic acid (NAA). In the sequence Kin-BA, the production of adventitious shoots decreased and reddish-coloured nodular structures (RNS) of meristematic appearance increased with increasing duration of Kin treatment, while somatic embryo formation was optimal at 8 d. In the Kin-TDZ sequence, shoot production was initially pronounced, but it declined with increasing duration of the Kin treatment, while the number of roots, somatic embryos and RNS increased. TDZ-BA treatments induced marked shoot production, which gradually increased with increasing duration of TDZ treatment. The presence of TDZ and a long treatment duration appeared to be very important factors in inducing caulogenesis. Kin appeared to be effective in shoot induction but not in shoot development; the results of this work demonstrate that RNS were adventitious shoots blocked at an early developmental stage on account of insufficient cytokinin activity. BA was less effective than TDZ in inducing shoot regeneration. Finally, both Kin and BA applied after 2,4-D treatment promoted somatic embryo induction.     

Surcose transport in isolated plasma-membrane vesicles from sugar beet (Beta vulgaris L.) Evidence for an electrogenic sucrose-proton symport

An analysis of the molecular mechanism of sucrose transport across the plasmalemma was conducted with isolated plasma-membrane (PM) vesicles. Plasma membrane was isolated by aqueous two-phase partitioning from fully expanded sugar beet (Beta vulgaris L.) leaves. The isolated fraction was predominantly PM vesicles as determined by marker-enzyme analysis, and the vesicles were oriented right-side-out as determined by structurally linked latency of the PM enzyme, vanadate-sensitive Mg²⁺-ATPase. Sucrose uptake was investigated by equilibrating PM vesicles in pH 7.6 buffer and diluting them 20-fold into pH 6.0 buffer. Using this pH-jump technique, vesicles accumulated acetate in a pH-dependent, protonophore-sensitive manner, which demonstrated the presence of a pH gradient (pH) across the vesicle membrane. Addition of sucrose to pH-jumped PM vesicles resulted in a pH-dependent, protonophoresensitive uptake of sucrose into the vesicles. Uptake was sucrose-specific in that a 10-fold excess of mannose, glucose, fructose, mannitol, melibiose, lactose or maltose did not inhibit sucrose accumulation. The rate of pH-dependent uptake was saturable with respect of sucrose concentration and had an apparent K _m, of 0.45 mM. Sucrose uptake was stimulated approximately twofold by the addition of valinomycin and K⁺, which indicated an electrogenic sucrose-H⁺ symport. Membrane potentials () were imposed across the vesicle membrane using valinomycin and K⁺. A membrane potential, negative inside, stimulated pH-dependent sucrose uptake while a , positive inside, inhibited uptake. Conditions that produce a negative in the absence of a pH gradient supported, although weakly, sucrose uptake. These data support an electrogenic sucrose-H⁺ symport as the mechanism of sucrose transport across the PM in Beta leaves.Abbreviations and symbols CCCP carbonyl cyanide m-chlorophenylhydrazone - cyt cytochrome - PM plasma-membrane(s) - electrical potential difference     

Regulation of the mitochondrial ATPasein situ in cardiac muscle: Role of the inhibitor subunit

The mitochondrial F₁-ATPase inhibitor protein, IF₁, binds to subunits of the F₁-ATPase bothin vitro andin situ under nonenergizing conditions, i.e., under conditions that allow a net hydrolysis of ATP by the mitochondrial ATPase to take place. This reversible IF₁ binding occurs in a wide variety of cell types including (anaerobic) baker's yeast cells and (ischemic) mammalian cardiomyocytes under conditions that limit oxidative phosphorylation. The binding of inhibitor results in a marked slowing of ATP hydrolysis by the undriven mitochondrial ATP synthase. An apparent main function of this reversible IF₁ binding, at least in cells that undergo aerobic-anaerobic switching, is the mitigation of a wasteful hydrolysis of ATP produced by glycolysis during anoxic or ischemic intervals, by the mitochondrial ATPase. While this apparent main function is probably of considerable importance in cells that normally either can or must undergo aerobic-anaerobic switching such as baker's yeast cells and skeletal myocytes, one wonders why a full complement of IF₁ has been retained in certain cells that normally do not undergo such aerobic-anaerobic switching, cells such as adult mammalian cardiomyocytes of many species. While some mammalian species have, indeed, not retained a functional complement of IF₁ in their cardiomyocytes, those that have can benefit significantly from its presence during intervals of myocardial ischemia.This mini-review is dedicated to the memory of Professor Efraim Racker.