Prenyl Chain Research Articles

Mevalonate-derived isopentenyl diphosphate is the biosynthetic precursor of ubiquinone prenyl side chain in tobacco BY-2 cells.

Study of the incorporation of 13C-labelled glucose or pyruvate into the isoprenoids of tobacco BY-2 cells allowed the biosynthetic origin of isopentenyl diphosphate to be determined. Sterols synthesized in the cytoplasm and the prenyl chain of ubiquinone Q10 located in mitochondria were derived from the same isopentenyl diphosphate pool, synthesized from acetyl-CoA through mevalonate, whereas the prenyl chain of plastoquinone was obtained from the mevalonate-independent glyceraldehyde 3-phosphate/pyruvate route, like all chloroplast isoprenoids from higher plants. These results are in accord with the compartmentation and complete enzymic independence of the biosynthesis of long-chain all-trans polyprenols in mitochondria and chloroplasts.

Biosynthesis of isoprenoids in higher plant chloroplasts proceeds via a mevalonate-independent pathway

Isopentenyl diphosphate (IPP) is the biological C 5 precursor of isoprenoids. By labeling experiments using [1- 13C]glucose, higher plants were shown to possess two distinct biosynthetic routes for IPP biosynthesis: while the cytoplasmic sterols were formed via the acetate/mevalonate pathway, the chloroplast-bound isoprenoids (β-carotene, lutein, prenyl chains of chlorophylls and plastoquinone-9) were synthesized via a novel IPP biosynthesis pathway (glyceraldehyde phosphate/pyruvate pathway) which was first found in eubacteria and a green alga. The dichotomy in isoprenoid biosynthesis in higher plants allows a reasonable interpretation of previous odd and inconclusive results concerning the biosynthesis of chloroplast isoprenoids, which so far had mainly been interpreted in the frame of models using compartmentation of the mevalonate pathway.

Conversion of Product Specificity of Archaebacterial Geranylgeranyl-diphosphate Synthase: IDENTIFICATION OF ESSENTIAL AMINO ACID RESIDUES FOR CHAIN LENGTH DETERMINATION OF PRENYLTRANSFERASE REACTION

Prenyltransferases catalyze the consecutive condensation of isopentenyl diphosphate with allylic diphosphates to produce prenyl diphosphates whose chain lengths are absolutely determined by each enzyme. To investigate the mechanism of the consecutive reaction and the determination of the ultimate chain length, a random mutational approach was planned. A geranylgeranyl-diphosphate synthase gene from Sulfolobus acidocaldarius was randomly mutagenized by NaNO2 treatment to construct a library of mutated geranylgeranyl-diphosphate synthase genes on a yeast expression vector. The library was screened for suppression of a pet phenotype of yeast C296-LH3, which is deficient in hexaprenyl-diphosphate synthase. Five mutants that could grow on a YEPG plate, which contained only glycerol as an energy source instead of glucose, were selected from approximately 1,400 mutants. All selected mutated enzymes catalyzed the formation of polyprenyl diphosphates with prenyl chains longer than geranylgeranyl diphosphate. Especially mutants 1, 3, and 5 showed the strongest elongation activity to produce large amounts of geranylfarnesyl diphosphate with a concomitant amount of hexaprenyl diphosphate. Sequence analysis revealed that each mutant contained a few amino acid substitutions and that the mutation of Phe-77, which is located on the fifth amino acid upstream from the first aspartate-rich consensus motif, is the most effective for elongating the ultimate product. Amino acid alignment of known prenyltransferases around this position and our previous observations on farnesyl-diphosphate synthase (Ohnuma, S.-i., Nakazawa, T., Hemmi, H., Hallberg, A.-M., Koyama, T., Ogura, K., and Nishino, T.(1996) J. Biol. Chem. 271, 10087-10095) clearly indicate that the amino acid at the position of all prenyltransferases must regulate the chain elongation.

Carotenoid biosynthesis in wild type and mutant strains of Mucor circinelloides

Carotenoid biosynthesis in wild type Mucor circinelloides has been investigated and the biochemical characterisation of the MS1 and MS9 mutant strains, impaired in carotenoid formation, carried out. In liquid cultures, all strains produced carotenoids (mainly β-carotene. but also ζ-carotene, lycopene and γ-carotene) at the onset of stationary phase of growth. Carotenogenesis was light dependent. In liquid cultures carotenoid formation in wild type was affected by diphenylamine, which prevented desaturation, nicotine, resulting in reduced carotenoid levels, but CPTA caused an increase in the total carotenoid content but a reduced β-carotene level, with the accumulation of lycopene and γ-carotene. The mutant strains MS1 and MS9 contained only 5.0 and 11.5% of wild type carotenoid levels, respectively. Cell extracts of light-grown mycelia, incubated with 3( R)-[2- 14C] mevalonic acid, produced β-carotene, but incorporations into carotenoids were substantially reduced in the cell extracts of MS1 and MS9. Analysis of prenyl diphosphate intermediates indicated that. compared to wild type, geranylgeranyl diphosphate accumulated in MS1. MS9 extracts produced a larger amount of prenyl phosphates and a more even distribution of radioactivity from mevalopic acid into farnesyl and geranylgeranyl diphosphates. Squalene and long chain prenyl phosphates were formed by the cell extracts of all strains. It is proposed that the MS1 strain possesses a mutation in a gene responsible for phytoene formation, whilst a regulatory mutation, affecting prenyl transferase activities, has occurred in MS9.

4-Isopropenyl-3-tosylmethyl pyrrolidines through radical cyclizations of 4-aza-1,6-dienes - an approach to kainic acids

The cyclofunctionalization of 4-aza-1,6-dienes 1 and 2 - bearing a prenyl chain - via the radical addition of PhSeTs ( 4) has been investigated as a potential route to 4-isopropenyl-3-tosylmethylpyrrolidines. Since the oxidative elimination of the resulting selenides afforded mainly the undesired olefinic regioisomer, an alternative pathway via the rearrangement of allylic sulfones 10–11, was applied and provided, in good yields, the target heterocycles; 12a, b are potential precursors of kainic acids.

ChemInform Abstract: Synthesis of Prenylated Quinones by the Oxydative Degradation Approach. Birch vs Vinylogous Birch Hydrogenolysis (BIHY vs VIBIHY) in Controlling 2δ‐Stereochemistry of the Prenyl Chain.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Synthesis of prenylated quinones by the oxidative degradation approach. Birch vs vinylogous Birch hydrogenolysis (BIHY vs VIBIHY) in controlling 2.DELTA. stereochemistry of the prenyl chain

Two novel approaches toward prenylated quinones are described. The first (route A) involves the following three basic operations: (a) construction of a 4-hydroxybezylamine carrying a tertiary allyl alcohol (cinnamyl alcohol) side chain of appropriate length (C 5 , C 10 , etc), followed by (b) vinylogous Birch reductive cleavage with concomitant isomerization of the double bond (vinylogous Birch hydrogenolysis, VIBIHY) and (c) Fremy's salt oxidative degradation of the resulting prenylated phenolic benzylamines to the corresponding quinones. Unfortunately, its stereochemistry cannot be properly controlled, as it leads to the formation of ca. 2.5:1 (E/Z)mixture of (Δ 2 )alkenes. The second generation approach (route B), which solves this problem, requires the following : (a) preparation of a 4-hydroxybenzylamine carrying a 3-methyl-2-buten-1-ol (dimethylallyl alcohol) side chain, or a higher homologue, followed by (b) Birch hydrogenolysis (BIHY) and step c above. The key Birch hydrogenolysis takes place with almost complete control of the stereochemically labile Δ 2 double bond, thereby making this approach the one of choice for the synthesis of isoprenyl benzoquinones

Kinetic studies on the prenyl chain elongation by undecaprenyl diphosphate synthase with artificial substrate homologues

In the undecaprenyl diphosphate synthase reaction, an allylic substrate homologue, (2 Z,6 E,10 E)-4-methyl-geranylgeranyl diphosphate was found to be a potent competitive inhibitor against the allylic primer, (2 Z,6 E,10 E)-geranylgeranyl diphosphate. On the other hand, it acted as a strong noncompetitive inhibitor against isopentenyl diphosphate. On the basis of these facts, the topology of the substrate-binding sites as well as the reason why the synthase reaction with ( E)-3-methyl-3-pentenyl diphosphate always stops completely at the first stage of condensation, yielding an allylic diphosphate with a methyl group at the 4-position, are discussed. Undecaprenyl diphosphate synthase; Prenyltransferase; Prenyl chain elongation; Polyprenyl diphosphate; Artificial substrate; Substrate homologue

Undecaprenyl diphosphate synthase reaction with artificial substrate homologues — novel behavior in the termination of prenyl chain elongation

( E )-3-Methyl-3-pentenyl diphosphate acted as an artificial homoallylic substrate in the reaction with several allylic diphosphates catalyzed by undecaprenyl diphosphate synthase of Bacillus subtilis . The synthase reaction with the artificial substrate proceeded in the same stereochemical manner as that with the natural homoallylic substrate, isopentenyl diphosphate, but it had a full stop at the stage where a single condensation of the C 6-homologue with an allylic primer is completed to form a chiral prenyl diphosphate with an extra methyl group at the 4-position. Allylic diphosphates that each have an extra methyl group at the 4-position were not accepted as substrates for this enzyme even when isopentenyl diphosphate was the homoallylic substrate.

ChemInform Abstract: Stereospecific Regulation of in vivo Prenyl Chain Elongation. Prenylation in Higher Plants

This article involves the brief explanation on the stereochemical picture of Cornforth's basic principle for the isoprenoid biosynthesis and the integrated presentation of new findings on the unusual prenyl chain elongation, which does not follow Cornforth's basic principle, in higher plants.The new findings are as follows : (i) In the biosynthesis of polyprenols from mevalonic acid by the intact leaves of Mallotus japonicus, the formation of their Z -prenyl chain involved the unusual elimination of the pro-4S hydrogen of the mevalonic acid. (ii) When (E, E) -farnesol was synthesized from 3, 3-dimethylallyl diphosphate (DMAPP) and isopentenyl diphosphate (IPP) in the presence of iodoacetamide with the cell-free extract of Pisum sativum, the DMAPP was condensed with the carbon-carbon double bond of IPP from its reversed face, i. e., re-re face. Stereospecific models for explanation of these unusual phenomena are presented.

生体内プレニル鎖延長反応の立体制御 高等植物におけるプレニル化

This article involves the brief explanation on the stereochemical picture of Cornforth's basic principle for the isoprenoid biosynthesis and the integrated presentation of new findings on the unusual prenyl chain elongation, which does not follow Cornforth's basic principle, in higher plants.The new findings are as follows : (i) In the biosynthesis of polyprenols from mevalonic acid by the intact leaves of Mallotus japonicus, the formation of their Z -prenyl chain involved the unusual elimination of the pro-4S hydrogen of the mevalonic acid. (ii) When (E, E) -farnesol was synthesized from 3, 3-dimethylallyl diphosphate (DMAPP) and isopentenyl diphosphate (IPP) in the presence of iodoacetamide with the cell-free extract of Pisum sativum, the DMAPP was condensed with the carbon-carbon double bond of IPP from its reversed face, i. e., re-re face. Stereospecific models for explanation of these unusual phenomena are presented.

Stereochemical analysis of prenyltransferase reactions leading to (Z)- and (E)-polyprenyl chains.

A feasible method was developed to determine the stereochemical direction of the C-C bond formation with respect to the face of the double bond of isopentenyl diphosphate in the prenyltransferase reactions. This method was applied to the reactions of undecaprenyl diphosphate synthase and heptaprenyl diphosphate synthase, which catalyze (Z)-prenyl chain elongation and (E)-prenyl chain elongation, respectively. In both cases, the C-C bond formation was found to take place at the si face of the double bond with elimination of one of the hydrogens of C-2 in a syn fashion.

Unusual contact allergens from plants in the family Hydrophyllaceae

The dermatitic constituents of the glandular hairs of plants in the family Hydrophyllaceae comprise a class of uncommon natural products called "phacelioids". The chemical structures consist of various elaborations of hydroquinone attached to a C10 to C20 prenyl chain. Certain of these compounds are equivalent to the urushiols of Toxicodendron (Rhus) in their capacity to sensitize humans. Although structurally related to the urushiols, the phacelioids do not appear to cross-react in humans either with urushiol, or between phacelioids with different prenyl chains.

Regulation of Prenyl Chain Synthesis in Etiolated Hordeum Seedlings by Far‐Red and White Light

AbstractThe kinetics of prenyl chain formation (C20 phytyl in chlorophylls, vitamin KI and α‐tocopherol; C40 carotenoids and C45 in plastoquinone‐9) in plastids of etiolated Hordeum seedlings was compared in continuous darkness and after far‐red and white light treatments: Continuous far‐red (via phytochrome Pfr) enhances the synthesis rate of all prenyl chains, but does practically not change the dark pattern of prenyl chain accumulation. Free C20 phytyl chains could not be detected by means of thin layer chromatography. White light induces a much stronger enhancement of prenyl chain formation than does far‐red. It also changes the pattern of prenyl chain synthesis by a particularly strong promotion of the synthesis of phytyl chains, which get bound to chlorophyll a. The rate of chlorophyllide formation seems to determine the rate of enhanced phytyl formation. It is assumed that the enzyme, which esterifies chlorophyllide a with the phytyl chain, is formed or activated by far‐red treatment, but only starts working in white light, when the protochlorophyllide holochrome is re‐arranged to the chlorophyllide holochrome.

The influence of continuous far-red and white light on prenyl chain synthesis in plastids of Raphanus seedlings

The rate of prenyl chain accumulation (C40 carotenoids; C45 in plastoquinone-9; C20 phytyl in chlorophylls, α-tocopherol and vitamin K1) in plastids of etiolated radish seedlings (Raphanus sativus L.) is determined in continuous darkness and after far-red and white light treatment. Continuous far-red light (active phytochrome P fr ) stimulates the synthesis of all prenyl chains, but has no or only little effect on the dark pattern of the prenyl chain formation. White light enhances the accumulation of prenyl chains to a much higher degree than does far-red light. By a particularly strong promotion of the accumulation of phytyl chains, which are incorporated into chlorophyll, white light changes the percentage composition of prenyl chains to that of chloroplasts.

Kinetic of lipoquinone and pigment synthesis in green Hordeum seedlings during an artificial day-night rhythm with a prolonged dark phase.

Abstract The effect of a prolonged darkness (48 h) with a following re-illumination on the prenyllipid metabolism of chloroplasts is tested in green Hordeum seedlings. Continuous darkness induces thylakoid and prenyllipid breakdown and changes the remaining lipoquinone and carotenoid metabolism of chloroplasts to that of etioplasts. Re-illumination, in turn, reverses the effects of darkness and regenerates the photosynthetic apparatus within 24 hours by a continuous and spe­cific synthesis of certain thylakoid prenyllipids. 1. The level of chlorophylls, vitamin K1 and that of the oxidized benzoquinone forms, plasto-quinone-9 and α-tocoquinone, decreases continuously in darkness. All these prenyllipids are re­ synthesized upon re-illumination, whereby a faster destruction rate in the dark (α-tocoquinone + plastoquinone-9 > vitamin K1 > chlorophylls) corresponds to a faster re-accumulation rate in the light. 2. The concentration of the reduced benzoquinones plastohvdroquinone-9 and α-tocopherol. which are preferentially deposited in the osmiophilic plastoglobuli, increases until 24 hours of dark­ness and decreases thereafter either continuously (plastohydroquinone-9) or exhibits another strong increase (α-tocopherol). Re-illumination results only in the accumulation of the oxidized quinone forms (mainly plastoquinone-9 and little α-tocoquinone) ; the level of plastohydroquinone remains, however, almost constant with a concomitant and steady decrease in the concentration of α-tocopherol. Darkness changes the main metabolite flow in benzoquinone synthesis via the formation of α-tocopherol (a trimethyl-, phythyl-(1,4-benzoquinone derivative) and light (re-illumination) via the production of plastoquinone-9 (a trimethyl, solanesyl-1.4-benzoquinone). 3. Carotenoids are enriched throughout the dark phase (mainly xanthophylls, little β-carotene) with a higher accumulation rate than after re-illumination, which yields again a higher portion of β-carotene. The correlation of prenyl chain synthesis (phytyl chain for chlorophylls and vitamin K1, solanesyl chain for plastoquinone-9) in the light with a reduced rate of carotenoid formation is discussed with respect to prenyl biosynthesis. 4. It is concluded that breakdown and re-synthesis of thylakoids and their prenyllipds, which are described here in a prolonged dark phase with following re-illumination, also occur during natural day-night growth of plants. The turnover of the thylakoid membranes and their lipids does, however, not get visible, since the decomposition in the night is recompensated by new synthesis during day. From the destruction rate one can calculate in a first approximation the biological half life time (τ 1/2) which gives values in the range of 7 to 2,5 days for all thylakoid prenyllipids

Die Wirkung von gibberellinsäure A3 und kinetin auf die bildung der photosynthesepigmente, lipochinone und anthocyane in Raphanus-keimlingen

1. Gibberellic acid (GA 3 , 10 ppm) has a rather stimulating effect on germination, but decreases the synthesis of chlorophylls, carotenoids, plastidic benzoquinones, and anthocyanins in Raphanus-seedlmgs (Z 0 -plants). It is assumed that GA 3 inhibits the light induced formation of thylakoids. When applied to the 3 day old seedlings (Z 3 -plants) during the investigation period (5 days) GA 3 decreases the formation of carotenoids, isoprenoid benzoquinones, and anthocyanins, while chlorophyll synthesis is not affected. Thus the degree of inhibition of prenyl-lipid synthesis by GA 3 depends on the developmental stage of the Rapbanus -seedYmg. 2. In the Z 0 -plants GA 3 induces a change of metabolite flow in the biosynthesis chain of lipoquinones which yields more α -tocopherol (+ α -tocoquinone) and less plastoquinone-9 (+ hydroquinone). This is inverse to the metabolite flow during active thylakoid synthesis. Z 3 -plants do not show this effect. 3. Parallel to the inhibition of prenyl-lipid synthesis GA 3 decreases in the Z 0 - and Z 3 -plants the rate of prenyl-chain formation. The synthesis of C 20 -chains in chlorophylls, α-tocopherol, and α-tocoquinone, and of C 40 -chains (carotenoids) is earlier affected than that of C 45 -chains in plastoquinone-9. 4. Kinetin (2 ppm) at first retards germination and development of Rapbanus -plants for about 3 days. Thereafter kinetin induces an increased growth of the seedlings, which results in a promoted synthesis of chlorophylls, plastoquinone-9 (+ hydroquinone), and anthocyanins. Formation of α -tocopherol (+ α -tocoquinone) in turn is suppressed. The data on the chloroplast lipids are consistent with the assumption that kinetin induces a promoted thylakoid synthesis. 5. In Z 0 - and Z 3 -plants kinetin decreases the synthesis of carotenoids. This is, however, a normal process during increased thylakoid synthesis, where formation of chlorophylls and plastoquinone-9 preceds that of carotenoids. Concerning the prenyl chains kinetin produces the formation and incorporation of the C 45 -chains in plastoquinone-9 and of phytyl chains in chlorophylls, which leaves apparently less isoprenoid C 20 -precursors for α-tocopherol and carotenoid synthesis. 6. Kinetin promotes — similar to β -indolacetic acid (IAA) — the light-dependant synthesis of chloroplast lipids and anthocyanins, while GA 3 — similar to abscisic acid (ABA) — inhibits these light effects (fig.1). Thus kinetin, IAA and light have a synergistic influence on Raphanns-plants. GA 3 and ABA, in turn, are antagonists to the light induced changes of plant metabolism.

Der einfluß von stickstoffmangel auf die lipochinon- und isoprenoid-synthese der chloroplasten von Hordeum vulgare L.

The synthesis of all thylakoid prenyl-lipids is lower during nitrogen deficiency than in normal green cultures. The inhibition observed is of different degree for the individual lipid classes: carotenoids, chlorophylls, prenyl chains, and the isoprenoid lipoquinones. 1. Carotenoid synthesis in nitrogen deficient (−N) and in normal green plants (+N) is strongly correlated with chlorophyll synthesis. The synthesis of both lipid classes is regulated with the formation of thylakoids. A specific change of chloroplast metabolism during nitrogen deficiency towards a promotion of the synthesis of the nitrogen-free carotenoids has not been observed. 2. The formation of the isoprenoid plastid-quinones during nitrogen deficiency is much less inhibited than that of carotenoids and chlorophylls. This is equally due for the naphthoquinone K 1 and the benzoquinone derivates. 3. On a chlorophyll basis the synthesis of vitamin K 1 and of the benzoquinones, plasto-quinone-9 (+ hydroquinone) and α-tocopherol (+ α-tocoquinone), is enhanced during nitrogen deficiency. It is assumed that a higher level of endogenous aromatic precursors, as caused by the inhibition of protein synthesis, is responsible for this promotion. 4. During nitrogen deficiency the reduced benzoquinone forms α-tocopherol and plasto-hydroquinone-9 are synthesized to a higher degree than in the controls. This is an indication for their deposition in the osmiophilic plastoglobuli. 5. On a chlorophyll a basis during nitrogen deficiency there are formed a relative higher portion of chlorophyll b, a lower portion of β-carotene, but more xanthophylls, and in the group of lipoquinones somewhat less plastoquinone-9 (+ hydroquinone) and more α-tocopherol (+ α-tocoquinone) than in the controls. It is postulated that a lower concentration of IAA (reduced synthesis of IAA during nitrogen deficiency) is responsible for these synthesis shifts within the lipid classes. 6. Inhibition and promotion of the synthesis of the different prenyl lipids is discussed in connection with their biosynthesis. Literatur

Die Hemmung der Carotinoidsynthese im Stickstoffmangel

The ability to synthesize carotenoids during normal or strongly reduced nitrogen supply was tested in a higher plant (Hordeum vulgare L.) and in a green alga (Scenedesmus obliquus). Though carotenoids are nitrogenfree, their synthesis is strongly inhibited during nitrogen deficiency. The formation of secondary carotenoids, which apparently proceeds at the expense of the primary carotenoid components, occurs in Scenedesmus but not in Hordeum plants. It is concluded that the dimerisation of geranly-geranyl-pyrophosphate is the limiting step in the carotenoid synthesis during nitrogen deficiency. The synthesis of prenyl chains is less affected by nitrogen deficiency.

3-Polyprenyl-4-hydroxybenzoate Synthesis in the Inner Membrane of Mitochondria from p-Hydroxybenzoate and Isopentenylpyrophosphate: A DEMONSTRATION OF ISOPRENOID SYNTHESIS IN RAT LIVER MITOCHONDRIA

Abstract The first intermediate in the conversion of p-hydroxybenzoate (PHB) to ubiquinone is a 3-polyprenyl derivative of PHB. Winrow and Rudney ((1969) Biochem. Biophys. Res. Commun. 37, 833) noted that in rat tissue minces and homogenates the synthesis of 3-polyprenyl-4-hydroxybenzoate (PPHB) required supplementation with an extract of Micrococcus lysodeikticus and isopentenylpyrophosphate. Under new conditions adopted by us the requirement for the M. lysodeikticus extract can be dispensed with and the synthesis of polyprenyl-p-hydroxybenzoate can be obtained solely from p-hydroxybenzoate, mevalonate, and ATP. Pulse chase experiments with labeled precursors in rat liver minces show a precursor-product relationship of PPHB and ubiquinone. It was found that PPHB was located primarily in the inner membrane of liver mitochondria. Mitochondrial preparations to which PHB, ATP, and mevalonate were added could not synthesize PPHB unless a supernatant fraction obtained by centrifugation of rat liver homogenates at 48,000 x g was added. The requirement for the supernatant fraction, ATP, and mevalonate could be dispensed with only if isopentenylpyrophosphate were added. This implied that mitochondria contain a system for synthesizing polyprenylpyrophosphate derivatives. This concept was unequivocally verified by demonstration of the presence of a sequence of key enzymes involved in polyprenyl synthesis, i.e. isopentenylpyrophosphate isomerase and diprenyltransferase, in the inner membrane of mitochondria. The nature of the PPHB formed in rat liver was investigated and it was found that in keeping with the known distribution of ubiquinone prenyl analogues UQ-9 and UQ-10 in rat liver the same proportion of 3-decaprenyl-4-hydroxybenzoate and 3-nonaprenyl-4-hydroxybenzoate could be formed. Guinea pig liver which is known to contain only UQ-10 was also shown to form only 3-decaprenyl-4-hydroxybenzoic acid. The enzyme alkylating PHB, i.e. PHB: polyprenyltransferase, has been shown to be unspecific with regard to the length of the polyprenyl side chain which it can transfer o PHB. The predominance of any prenyl analogue of UQ in a tissue depends upon the specificity of the system which determines the length of the polyprenylpyrophosphate chains synthesized in mitochondria. Conditions for the optimal synthesis of PPHB from PHB and isopentenylpyrophosphate in mitochondria are described. The effect of CoA-SH was investigated on PPHB formation and was found to be either nonexistent or stimulatory depending on the medium in which the synthesis was carried out. In the latter case CoA-SH increased the amount of shorter chain prenyl analogues of PHB. The results, providing the first demonstration that a system of enzymes for synthesizing polyprenylpyrophosphate chains exists in the inner mitochondrial membrane, are of great biological significance in view of the increasing role that these compounds play in the transfer of sugars to glycoproteins. Several other possible roles for polyprenylpyrophosphate compounds in mitochondria are discussed.