The biological significance of glycyrrhizin- and glycyrrhetinic acid derivative-induced selective phosphorylation of histones H2A and H2B by A-kinase in vitro

Histones H2A and H2B were found to be glycyrrhizin (GL)-binding proteins, because (i) the two histones H2A-H2B pairs were isolated selectively from the crude histone preparations of calf thymus by means of GL-affinity column chromatography (HPLC); (ii) phosphorylation of these two histones by A-kinase was remarkably stimulated by native GL or oGA (a derivative of glycyrrhetinic acid) at 20 microM; and (iii) in the crude histone preparations of calf thymus, these two histones were selectively phosphorylated by A-kinase in the presence of both dsDNA and 20 microM oGA or 20 microM GL. The provided data suggest that the GL-induced selective phosphorylation of histones H2A and H2B by A-kinase may be implicated in the transcriptional activation involved in the biological activities of the drug.

[Effect of verapamil on myocardial ischemia in patients with hypertrophic cardiomyopathy: evaluation by exercise thallium-201 SPECT]

The effect of verapamil on myocardial ischemia in patients with hypertrophic cardiomyopathy (HCM) was evaluated by exercise myocardial 201Tl SPECT (EX-Tl). EX-Tl was performed before and after 8.1 +/- 6.1 weeks of oral administration of verapamil (240 mg/day) on 20 patients with HCM who showed transient 201Tl perfusion defects under control conditions. SPECT images were divided into nine segments. The 201Tl perfusion defect was visually scored and evaluated for four grades in each segment and the sum total grade was calculated as the defect score. Transient dilation index was calculated as a reflection of subendocardial ischemia. Improvements in defect score were demonstrated in 18 of 20 patients after administration of verapamil. The mean defect score decreased significantly from 5.1 +/- 2.3 to 2.5 +/- 2.4 (p < 0.001). Although 18 of 20 patients showed abnormal transient dilation index under control conditions, 16 showed improvement and 12 were normalized after verapamil therapy. Mean transient dilation index decreased from 1.24 +/- 0.19 to 1.08 +/- 0.10 (p < 0.01). Verapamil improves myocardial ischemia in patients with HCM.

Biochemical characterization of a 34 kDa ribonucleoprotein (p34) purified from the spinach chloroplast fraction as an effective phosphate acceptor for casein kinase II

A 34 kDa ribonucleoprotein (p34) was purified to homogeneity from a 1.0 M KCl extract of spinach chloroplasts and characterized as an effective phosphate acceptor for casein kinase II (CK-II). The N-terminal 21 residues (W-V-A-Q-T-S-E-E-E-Q-E-G-S-T-N-A-V-L-E-G-E) of p34 were 95% identical with the sequence reported for 28RNP (plastid mRNA 3' end processing factor in chloroplast). Moreover, the findings that DNAs as well as RNAs significantly stimulate the CK-II catalyzed phosphorylation of p34 in vitro and induce its conformational change, suggest that the physiological activity of p34-bound RNA or DNA in chloroplast post-transcriptional regulation is controlled by specific p34 phosphorylation by CK-II.

[Assessment of myocardial perfusion abnormalities in patients with apical hypertrophic cardiomyopathy using exercise 201Tl scintigraphy]

Regional myocardial perfusion abnormalities commonly occur during exercise in patients with hypertrophic cardiomyopathy (HCM). Exercise 201Tl myocardial scintigraphy has provided a noninvasive means of identifying myocardial perfusion abnormalities in patients with HCM. On the other hand, apical hypertrophic cardiomyopathy (APH) is reported as a subtype of HCM. Whether APH is essentially equal to HCM or not is controversial. To assess myocardial ischemia in patients with APH, we studied 28 patients with APH, with exercise 201Tl SPECT. Myocardial perfusion images were obtained immediately after submaximal exercise and again after a 3-hour delay. Regional perfusion defects during exercise were identified in 19 of the 28 patients (68%) with APH. Complete reversible defects were observed in 15 (79%) patients with APH. Although perfusion defects were present in all regions of the left ventricle in patients with HCM, they were present only in the apical region in patients with APH. Thus, reversible 201Tl perfusion abnormalities commonly occur during exercise in patients with APH as well as in patients with HCM.

Phosphorylation of Mg(2+)-dependent protein phosphatase alpha (type 2C alpha) by casein kinase II

In this study we show that rat Mg(2+)-dependent protein phosphatase alpha (MPP alpha) expressed in Saccharomyces cerevisiae cells was phosphorylated on serine residues in vivo. The recombinant rat MPP alpha purified from Escherichia coli cells harboring an expression vector was phosphorylated in vitro by casein kinase II, but not by casein kinase I, to 1.5 mol phosphate per mol enzyme protein. Analysis by phosphopeptide mapping and amino acid analysis suggested that the sites of both in vivo and in vitro phosphorylation were the same and involved only serine residues. These results suggest that the rat MPP alpha expressed in yeast cells is phosphorylated by yeast casein kinase II in vivo. It is further proposed that the phosphorylation sites are located in the carboxyl terminal region of the enzyme molecule.

Characterization of casein kinase II, and of p98 as one of its effective phosphate acceptors in sea urchin eggs

CK-II has been partially purified from a 1.5 M KCl extract of unfertilized sea urchin eggs by means of DEAE-cellulose column chromatography, gel filtration on Sephacryl S300, and heparin-agarose column chromatography, successively. This partially purified CK-II was associated with a 98 kDa polypeptide (designated as p98), which was then separated from the kinase by Mono Q column chromatography (HPLC). The biochemical characteristics of CK-II purified from unfertilized eggs were similar to those of CK-IIs from various mammalian cells: requirements of divalent cations (Mg2+ and Mn2+) and phosphate acceptors (casein and p98), response to basic polypeptides and heparin, subunit structure and molecular size. Moreover, it was found that: (i) p98 (apparent pI 10.0) has DNA-binding ability and functions as an effective phosphate acceptor for CK-II in vitro; (ii) phosphorylation of p98 by the kinase was highly stimulated by histone-like sperm protein from sea urchin sperm, protamine (salmon sperm), and poly Arg; and (iii) selective phosphorylation of p98 by CK-II was detected when the DEAE-cellulose fraction from unfertilized eggs was incubated with [gamma-32P]ATP in the presence of protamine. Some biochemical characteristics of p98 from the eggs were similar to those of transcriptional factor Sp1. The evidence obtained suggests that (i) arginine-rich sperm proteins function as potent activators for CK-II in unfertilized eggs and (ii) specific phosphorylation of p98 by the activated kinase may play an important role in the transcriptional regulation in the eggs accompanying fertilization.

The stimulatory and inhibitory effects of glycyrrhizin and a glycyrrhetinic acid derivative on phosphorylation of lipocortin I by A-kinase in vitro

The effects of GL and oGA on the activity (phosphorylation of lipocortin I) by A-kinase were investigated in vitro. It was found that (i) phosphorylation of the 35-36 kDa polypeptide by A-kinase was inhibited selectively when the partially purified kinase fraction from EAT cells was incubated with [gamma-32P]ATP in the presence of 60 microM oGA; (ii) the marked polypeptide was identified as a lipocortin I; and (iii) the activity of the kinase was stimulated about 4-fold by 5 microM oGA, but it was inhibited at doses above 25 microM. The drug-induced inhibition of phosphorylation of lipocortin I by A-kinase may be implicated in the anti-inflammatory effect of the drugs.

[Repeated blackout in a patient with accelerated idioventricular rhythm]

There has been no report that Accelerated Idioventricular rhythm (AIVR) causes a syncope attack. The patient described in this report is very rare because AIVR chronic without any heart diseases has been observed for 13 years, and because it is considered that AIVR is closely associated with his repeated blackouts. A 62-year-old male was admitted to our hospital because of repeated syncopal attacks. He reported that he occasionally felt lightheaded after strenuous lifting and pushing or pulling against resistance. We found that AIVR could produce a remarkable arterial pressure drop partly because of ventricular asynergy and loss of timed atrial contribution. Furthermore, we observed syncopal attacks during Valsalva maneuver and found abnormalities of baroreceptor reflex (Lack of reflex tachycardia and weakened evershoot phenomenon). It is concluded that AIVR is not a benign arrhythmia in this patient because it has been a possible cause of syncope attack due to systemic arterial pressure drop and baroreceptor abnormalities.

Selective purification of two distinct protein kinases (C-kinase and casein kinase II) from the membrane fraction of mouse brain by NED-affinity column chromatography

By means of NED-affinity column chromatography, two distinct protein kinases have been selectively purified from the crude membrane extract of mouse brain. One (designated P-I kinase) was eluted from the column by the buffer containing 5 mM EGTA and the other (designated P-II kinase) was eluted by the buffer containing 0.6 M KCl. The activity of A-kinase was detected in the column passed through fraction. Biochemical characteristics of P-I and P-II kinases corresponded exactly to those of C-kinase and casein kinase II (CK-II), respectively. In addition, immunoprecipitate experiment using anti-CK-II antiserum against the beta-subunit of Drosophila CK-II showed that P-II kinase is identical to CK-II and the 62 kDa cellular polypeptide is associated with the kinase.

[Comparative study of postoperative complications in primary and secondary implantation of posterior chamber intraocular lens in cataract surgery for diabetic patients]

Postoperative complications of diabetic cataract cases with active stage diabetic retinopathy, which underwent simultaneous extracapsular lens extraction (ECCE) and posterior chamber intraocular lens (PC-IOL) implantation in 84 eyes, ECCE only in 38 eyes and secondary implantation of PC-IOL after ECCE in 23 eyes, were studied. In the eyes of the primary PC-IOL implantation group, fibrous response in 35 eyes (42%), posterior iris synechia in 10 eyes (12%), progression of diabetic retinopathy in 13 eyes (16%), after cataract in 11 eyes (13%), pupil capture in 4 eyes (5%) and decentration of lens optics in 3 eyes (4%) were appeared, while in the ECCE only group, fibrous response in 11 eyes (29%), posterior iris synechia in 4 eyes (11%), after cataract in 11 eyes (29%), progression of diabetic retinopathy in 6 eyes (16%) were observed. On the other hand, in the secondary PC-IOL implantation group, only fibrous response was appeared in 1 eye (4%), Although PC-IOL implantation has been so far considered contraindication in cases with cataract combined with active stage retinopathy, the present studies strongly suggest that secondary PC-IOL implantation would be good indication in these cases whose blood sugar was properly controlled and the retinopathy was burned out by panretinal photocoagulation soon after ECCE.

[Clinical evaluation of 123I-BMIPP myocardial scintigraphy in patients with hypertrophic cardiomyopathy]

123I-BMIPP myocardial scintigraphy was performed in 13 patients with hypertrophic cardiomyopathy and compared with 201Tl myocardial scintigraphy performed within 3 months for evaluating the clinical significance of 123I-BMIPP myocardial scintigraphy. SPECT images were divided into 13 segments and segmental images were visually scored on a 4 (increased tracer uptake) to 0 (severely decreased tracer uptake) scale according to the tracer uptake. In comparison of 123I-BMIPP early images and 201Tl perfusion images, mismatches were seen in about 70% of all segments. The number of segments demonstrating lower myocardial uptake of 123I-BMIPP was larger than that of 201Tl. In hypertrophic regions, the tracer uptake of 123I-BMIPP early images was significantly lower than that of 201Tl images and the lower uptake of 123I-BMIPP delayed images was more marked. In non-hypertrophic regions, no significant difference was seen between the tracer uptakes of 123I-BMIPP early images and 201Tl images but the tracer uptake of 123I-BMIPP delayed images was significantly lower than that of 201Tl images. The mismatch between the tracer uptakes of 123I-BMIPP images and 201Tl images was thought to be a reflection of disordered myocardial fatty acid metabolism. "Washout", the difference between the tracer uptakes of 123I-BMIPP early images and delayed images was also thought to be a reflection of disordered myocardial fatty acid metabolism. These results suggest that 123I-BMIPP is a promising radiopharmaceutical for evaluating disordered myocardial fatty acid metabolism in patients with HCM.

The in vitro effects of glycyrrhizin and the derivatives of glycyrrhetinic acid on the activity of cAMP-dependent protein kinase and phosphorylation of cellular polypeptide by the kinase from Ehrlich ascites tumor cells

The effects of glycyrrhizin (GL) and the derivatives of glycyrrhetinic acid (GA) on the activity of cAMP-dependent protein kinase (A-kinase) and the phosphorylation of cellular polypeptides by the kinase purified from Ehrlich ascites tumor cells had been investigated in vitro. It was found that (i) the derivatives [3 beta-hydroxy-olean-11,13 (18)-diene-30-oic acid Na, olean-9(11), 12 diene-3 beta, 30-diol-3 beta, 30-di-o-hemiphthalate 2Na and olean-12-ene-3 beta, 30-diol 3 beta, 30-di-o-phosphate 2Na] of GA inhibited the activity of A-kinase at the concentrations higher than 25 microM; (ii), at 10 microM, these derivatives and native GL stimulated the activity of the kinase significantly; and (iii) the inhibitory and stimulatory effects of some GA derivatives were clearly correlated with their chemical structures. Moreover, sodium dodecyl sulfate polyacrylamide gel electrophoresis and two dimensional gel electrophoresis followed by autoradiography detected several acidic polypeptides, including polypeptides with approximate molecular weights of 35,000 (pI 4.3), 27,000 (pI 4.5) and 18,000-21,000 (pI 4.5), phosphorylated by A-kinase, to be functioning as mediators in response to these drugs. This observation suggests that the GL-induced inhibition of phosphorylation of these cellular polypeptides by A-kinase may be physiologically implicated in the biochemical mechanisms involved in the anti-inflammatory effect of the drug.

[Effect of age on visualization of right atrium by thallium-201 myocardial scintigraphy]

With Thallium-201 (Tl) myocardial scintigraphy, right atrial (RA) myocardium has been visible in the disease involving the right side of the heart. We have found RA visualization in the elderly patients without the evidence of right heart disease. Therefore, we studied the relation of age to the RA visualization with Tl myocardial scintigraphy performed at rest. Planar images of 291 patients without valvular or congenital heart disease were read by two observers and classified into the three by the degree of RA visualization; RA 0 = not visualized, RA 1+ = moderately visualized, RA 2+ = intensely visualized. The results were as follows: 93.1% of under 50 y.o., 77.8% of fifties, 86.7% of sixties, 50.5% of seventies and 36.7% of over 80 y.o. showed RA 0. 6.9% of under 50 y.o., 22.2% of fifties, 8.3% of sixties, 46.5% of seventies and 36.7% of over 80 y.o. showed RA 1+. None of under 60 y.o., 5.0% of sixties, 3.0% of seventies, and 26.6% of over 80 y.o. showed RA 2+. In conclusion, RA visualization in Tl myocardial scintigraphy, suggesting right heart overload, may increase with aging.

Involvement of thromboxane A2, leukotrienes and free radicals in puromycin nephrosis in rats

Thromboxane A2 (TXA2), leukotrienes (LTs) and free radicals are considered to be possible mediators in the induction of glomerular injury and proteinuria. In this study, we examined the involvement of these three mediators and the protective effect of simultaneous inhibition of all three in puromycin aminonucleoside (PAN) nephrosis in rats. A single intraperitoneal injection of PAN (100 mg/kg) induced massive proteinuria and enhanced production of TXA2 and LTs from arachidonic acid in renal cortical slices and renal glomeruli, and increased malondialdehyde levels in plasma, urine and renal cortex. Oral administration of CV-6504(HCl) (3 to 20 mg/kg/day, for 1 to 2 weeks), a novel treble inhibitor of TXA2 synthetase, 5-lipoxygenase and lipid peroxidation, dose-dependently attenuated PAN-induced proteinuria and the increases in these three mediators. Any single specific inhibitor (CV-4151, a TXA2 synthetase inhibitor; AA-861, a 5-lipoxygenase inhibitor; or CV-3611, a radical scavenger) or a combination of two inhibitors showed no or only a slight antiproteinuric effect, but the combination of all three inhibitors significantly reduced PAN-induced proteinuria. These results suggest that, these three mediators may be involved in the pathogenesis of PAN nephrosis and that CV-6504(HCl), which can simultaneously inhibit all three, may be a useful therapeutic agent for nephrosis.

Characterization of a basic polypeptide-activated protein kinase in the eggs of the silkworm, Bombyx mori

A basic polypeptide-activated protein kinase (designated BA-kinase), which requires Mn2+ rather than Mg2+ for its activity, has been highly purified from a 1.5 M KCl extract of fertilized and unfertilized eggs of the silkworm, Bombyx mori. It was found that (i) the molecular weight of the purified protein kinase was approx. 260,000; (ii) the kinase phosphorylated vitellin, protamine and casein in a cAMP-, cGMP- and Ca2(+)-independent manner; (iii) the kinase phosphorylated only threonine residues when casein was used as a phosphate acceptor; (iv) protein phosphorylation by the kinase was remarkably stimulated by basic polypeptides, such as histone, polyArg and polyLys; and (v) the purified kinase had an affinity with DNA, but not with RNAs. Moreover, the observations that (a) the BA-kinase activity and phosphorylation of polypeptides by the kinase in the 1.5 M KCl egg extract greatly increased after fertilization, and (b) polypeptides, from this extract, of 16.5-21 kDa, which were highly phosphorylated by the kinase but not by A- or G-kinases, appeared within 4 h after fertilization, suggest that a basic polypeptide activated protein kinase (BA-kinase) may play an important role in the progression of embryogenesis through specific phosphorylation of yolk proteins by the kinase, in the presence of nucleic basic proteins.

Biochemical characterization of the membrane-associated phosphorylating proteins involved in the anti-proliferative effect of human recombinant interferon-alpha 2a (rIFN-alpha 2a) in Daudi cells

The anti-proliferative effect of interferons (IFNs) was investigated, focusing on the physiological activities of membrane-associated proteins involved in the progress of cell proliferation. In preliminary screening of the inhibitory effect of IFNs against the cell growth of various human hematopoietic tumor cells, Daudi cell was the most sensitive to rIFN-alpha 2a. SDS-PAGE followed by autoradiography detected that treatment of Daudi cells with rIFN-alpha 2a significantly reduced phosphorylation of the membrane-associated Mr 98,000 and 70,000 polypeptides. To determine the physiological significance of these phosphorylating polypeptides in mediation of the IFN effects, they were purified from Daudi cells. It was found that the molecular weight of the purified polypeptides was approximately 330,000 and it (designated 330-kDa protein) was consist of two distinct subunits [alpha-subunit (Mr 98,000) and beta-subunit (Mr 70,000)]. The biochemical properties, such as subunit structure, subunit phosphorylation, requirements for phosphorylating activity and protease sensitivity of the 330-kDa protein were similar to those reported for Na+, K(+)-ATPase. Evidence provided here suggests that the anti-proliferative action of IFNs may, at least in part, be implicated in the IFN-induced physiological impairment of the membrane-associated 330-kDa protein.

Characterization of glycyrrhizin-binding protein kinase from the crude membrane fraction of rat liver

Using GL-affinity column chromatography, a casein phosphorylating protein kinase was purified selectively from the crude membrane fraction of rat liver. The biochemical characteristics of the purified kinase (approximately Mr 210 kDa) are very similar to those reported for polypeptide-dependent protein kinase (kinase P). Moreover, low doses of GL selectively inhibit phosphorylation of Mr 35-36 kDa polypeptides (which are cross-reacted with anti-lipocortins I and II) by the kinase in vitro. These results suggest that the anti-inflammatory activity of GL may involve the impairment of the physiological functions of lipocortins through their specific modification by the kinase at the cell membrane level.

Inhibitory effect of glycyrrhizin on polypeptide phosphorylation by polypeptide-dependent protein kinase (kinase P) in vitro

The anti-viral mechanism of glycyrrhizin (GL) has been investigated by considering in vitro effects on polypeptide phosphorylation. It was found that GL (i), at low doses, selectively inhibits protein phosphorylation by Kinase P, but has not significant effects on the activities of other kinases (Kinase A, Kinase C and histone kinase); (ii) binds directly to Kinase P and reduces kinase activity in a dose-dependent manner; and (iii) inhibits vesicular stomatitis virus (VSV)-associated kinase activity. These observations strongly suggest that direct binding of GL to the virus causes the direct inactivation of virus-associated kinase and the reduction of the viral infectivity.

Purification and characterization of a 400-kDa nonhistone chromatin protein that serves as an effective phosphate acceptor for casein kinase II from Ehrlich ascites tumor cells

A nonhistone chromatin protein (NHCP) has been purified to homogeneity from a 0.5 M NaCl extract of Ehrlich ascites tumor cell (EAT cell) nuclei as a phosphate acceptor for casein kinase II using ion-exchange column chromatographies and Sephacryl S300 gel filtration. The purified NHCP (approximate Mr = 400,000) was found to be a tetramer of an Mr = 98,000 polypeptide (pI = 6.9) and to have high contents of glycine (15%) and serine (11.6%). This protein (designated as 400-kDa NHCP) was highly phosphorylated by casein kinase II (Mr = 130,000), but not by histone kinase. Casein kinase II phosphorylated only seryl residues of the purified 400-kDa NHCP. The NHCP bound with DNA, but not with RNAs, and the DNA binding ability of the protein was reduced when it was phosphorylated by casein kinase II. Moreover, we found that (a) the 400-kDa NHCP is present in large quantities in malignant mouse cells, such as EAT, EL-4, and Meth-A cells, but only slightly in normal tissues and cells; (b) the protein level is rapidly increased when mouse lymphocytes are treated with recombinant interleukin 2 (T cell growth factor) or concanavalin A; and (c) the kinase responsible for the 400-kDa NHCP phosphorylation in the chromatin of various mouse cells is a casein kinase II. These experimental results suggest that the 400-kDa NHCP acts as an effective phosphate acceptor for casein kinase II at the chromatin level and that an increased phosphorylation of the protein by the kinase may be implicated in the progress of cell differentiation and proliferation.

Characterization of a polypeptide-dependent membrane protein kinase that specifically phosphorylates NS protein of vesicular stomatitis virus in vitro

Phosphorylation of membrane-associated proteins by protein kinases in the membrane fraction from HeLa S3 cells was rapidly increased when the cells were infected with vesicular stomatitis virus (VSV). SDS-PAGE followed by autoradiography revealed polypeptides with molecular sizes of Mr. 53,000, 44,000, 42,000, 35,000, 30,000 and 27,000 in the kinase fraction from uninfected cells to be highly phosphorylated. Virus-coding NS protein (Mr. 40,000) was phosphorylated when the membrane fraction from virus-infected cells was incubated with [gamma-32P]ATP in the presence of histone H1 and Mg2+. Under these conditions, histone H1 functioned as a stimulator for NS protein phosphorylation by the kinases. One (kinase III) of the membrane-associated kinases was partially purified from HeLa S3 cells using FPLC (type Mono Q) after DEAE-cellulose column chromatography. The enzymatic properties of kinase III were similar to those reported for a polypeptide-dependent protein kinase (protein kinase P), because (a) both kinases highly phosphorylated beta-casein, although no phosphorylation was observed with histones; (b) several endogenous substrates from HeLa S3 cell membrane were phosphorylated by the kinases in the presence of basic proteins, such as histones, protamine and poly-Lys; (c) their activity was insensitive to a low concentration (19 micrograms/ml) of heparin, which highly inhibited casein kinase II activity; and (d) the kinases were extractable from the plasma membrane using Triton X-100. In addition, provided evidence suggests that kinase III may play an important role in an early stage of VSV replication through its specific phosphorylation of NS protein and membrane proteins in virus infected cells.

Direct activation of guanine nucleotide binding proteins through a high-energy phosphate-transfer by nucleoside diphosphate-kinase

An in vitro study of phosphate-transfer, from the high-energy phosphates on the phosphoenzyme (enzyme-bound high-energy phosphate intermediate) of NDP-kinase to GDP on various guanine nucleotide binding proteins (G1, elongation factor alpha 1, recombinant v-rasH p21 protein, transducin, Gi and Go), revealed that the GDP acts as a phosphate-acceptor, in the presence of divalent cations (Mg2+ and Ca2+). This finding suggests that via phosphate-transfer, NDP-kinase may be responsible for the direct activation of various guanine nucleotide binding proteins through phosphate-transfer by the enzyme.

Physiological correlation between nucleoside-diphosphate kinases and the 21-kDa guanine-nucleotide binding proteins copurified with the enzymes from the cell membrane fractions of Ehrlich ascites tumor cells

The physiological correlation between nucleoside-diphosphate kinases (NDP-kinases) and the 21-kDa guanine nucleotide-binding proteins (G1 and G2) which are copurified with the enzymes from the cell membrane fractions of Ehrlich ascites tumor cells has been biochemically investigated in vitro. We found that: incubation of the phosphoenzyme (enzyme-bound high-energy phosphate intermediate) of NDP-kinases (F-I and F-II) with one of the nucleoside 5'-diphosphates in the presence of 1 mM Mg2+ or 0.25 mM Ca2+ results in the rapid formation of nucleoside 5'-triphosphates without strict base specificity; GDP on the guanine nucleotide-binding proteins (G1, G2 and recombinant v-rasH p21) acts as a phosphate acceptor for the high-energy phosphates of the phosphoenzyme in the presence of 0.25 mM Ca2+; and [32P]GTP is preferentially formed from the 32P-labelled phosphoenzyme F-I and GDP-bound G1 or GDP-bound recombinant v-rasH p21 protein, even if any other nucleoside 5'-diphosphates are present in the reaction mixture. Although [32P]GTP formed was bound with the guanine nucleotide-binding proteins, it was immediately hydrolyzed by the proteins themselves in the presence of 5 mM Mg2+, but not in the presence of 0.25 mM Ca2+. Available evidence suggests that NDP-kinase may be responsible for the activation of the guanine nucleotide-binding proteins (G1, G2 and p21 proteins) through phosphate transfer by the enzyme.