Paying the price for standing tall: Fluid mechanics of prostate pathology

BACKGROUND

Age-dependent increase in the incidence of benign prostatic hyperplasia (BPH) and prostate cancer (PCa) are both related to cell proliferation and survival controlled by intraprostatic free testosterone (FT) concentration. Paradoxically, BPH and PCa occur as circulating testosterone levels decrease, so any possible relationship between testosterone levels and development of BPH and PCa remains obscure.

RESULTS

In BPH the enlarging prostate is exposed to high testosterone levels arriving directly from the testes at concentrations about hundredfold higher than systemic FT. This occurs because venous blood from the testes is diverted into the prostate due to the elevated hydrostatic pressure of blood in the internal spermatic veins (ISVs). Elevated pressure is caused by the destruction of one-way valves (clinically detected as varicocele), a unique phenomenon related to human erect posture. While standing, human males are ISVs vertically oriented, resulting in high intraluminal hydrostatic pressures-a phenomenon not found in quadrupeds. In this communication, we demonstrate the fluid mechanics' phenomena at the basis of varicocele leading to prostate pathology.

CONCLUSIONS

So far, varicocele has been studied mostly for its etiologic role in male infertility and, thus, for its effects on the testes. It is becoming clear that varicocele is a major etiologic factor in BPH and likely also in PCa. Restoring normal testicular venous pressure by treatment of the abnormal ISV's in varicocele has been shown to avert the flow from the prostate with the effect of reducing prostate volume, alleviating symptoms of BPH, and increasing concentrations of circulating FT.

Azoospermia and maturation arrest: malfunction of valves in erect poster of humans leads to hypoxia in sperm production site

Maturation arrest (MA) of spermatogenesis is diagnosed on histology as interruption of spermatogenesis before the final stage without impairment of Sertoli or Leydig cells. It is considered a condition of irreversible or absolute infertility. Varicocele, which represents impairment in the testicular venous drainage system, has been shown to be a bilateral disease. Malfunction of the valves increase the hydrostatic pressure in the testicular venous system that exceeds the pressure in the arterial system leading to hypoxia in the testicular microcirculation and in the seminiferous tubules, the sperm production site. Sperm production deteriorates, and ultimately progresses to azoospermia. Our prediction was that MA, if genetic factors are excluded, is the final stage of long standing hypoxia. This would indicate that MA is not always an independent disease entity, but may represent progressive process of deterioration of the testicular parenchyma beyond azoospermia. By histology and electron microscopy, our prediction confirmed, at least partially, that MA is associated with degenerative ischaemic changes in the seminiferous tubules. Adequate treatment of bilateral varicocele by microsurgery or super-selective sclerotherapy of the internal spermatic veins including associated network of venous bypasses, vertically oriented, may resume the flow of oxygenated blood. If irreversible damages did not occur and ischaemia is not too long standing, limited sperm production may be restored, at least partially.

Is varicocele prevalence increasing with age?

Varicocele is a bilateral vascular disease which occurs when the one-way valves in the internal spermatic veins, the testicular venous drainage system, malfunction. Based on new findings and fluid-mechanics analysis we showed that this process results in vertical blood columns, which cause pathological hydrostatic pressure in the testicular venous microcirculatory system. Ultimately, these pressures exceed the pressure in the arteriolar system. This unique phenomenon of reversal of pressures gradient between the arteriolar and venular systems leads to persistent hypoxia in the testosterone production site, namely, the Leydig cells. The result of bilateral varicocele is decreased testosterone production. Adequate treatment of bilateral varicocele significantly elevates the testosterone production. We found that the prevalence of varicocele increases with age with a rise of about 10% for each decade of life with the incidence reaching 75% in the eight decade of life. Based on our findings the following statements can be made: (1) varicocele prevalence is increased over time. (2) The rise of the incidence is about 10% for each decade of life. (3) 75% of men in the eight decade of their life have varicocele. As varicocele decreases testosterone production and it is reversible by appropriate treatment, it raises two interesting and important issues to be studied: (i) it is possible that varicocele accelerates the process of the ageing male. (ii) It is possible to retard, at least partially, the process of ageing in men by adequate treatment of bilateral varicocele.

Right varicocele and hypoxia, crucial factors in male infertility: fluid mechanics analysis of the impaired testicular drainage system

Varicocele is considered a predominantly unilateral left-sided disease. However, since male fertility is preserved with only one healthy testis, infertility perforce represents bilateral testicular dysfunction. It was hypothesized that: (i) right varicocele cannot be diagnosed by palpation and therefore has not been treated in the past by the traditional treatment, and (ii) right varicocele causes impaired oxygen supply in the right testicular microcirculation, leading to germ cell degeneration. This study performed venographies of both right and left internal spermatic veins during the treatment of 840 infertile men with varicocele and analysed the results using tools of fluid mechanics. Histopathology of the right testis revealed stagnation of blood flow and degenerative changes attributed to lack of adequate oxygenation in all testicular cell types. Right varicocele was found in the vast majority of the patients. We found that due to the destruction of one-way valves, pathologic hydrostatic pressure is produced in the testicular venous microcirculatory system about five times higher than normal, exceeding arteriolar pressure. The pressure gradient between the arterioles and venules in the testicular tissue is therefore reversed, leading to persistent hypoxia. Right varicocele, although undetected, is prevalent in infertile men with varicocele, hence only bilateral occlusion of the internal spermatic veins, including the associated bypasses, eliminating the pathologic hydrostatic pressure will lead to resumption of arterial blood flow in the testicular microcirculation.

A Proposed Anatomic Typing of the Right Internal Spermatic Vein: Importance for Percutaneous Sclerotherapy of Varicocele

PURPOSE

To classify the anatomic types of the right internal spermatic vein (ISV).

METHODS

We evaluated venograms obtained in 150 consecutive patients with idiopathic varicocele referred for transfemoral sclerotherapy.

RESULTS

Six anatomic types of the right internal spermatic vein (ISV) were recognized. These were classified by the location of their orifices and the tributary venous patterns. In roughly half the patients (53%), the ISV appeared as a simple vein with no remarkable retroperitoneal interconnections. In the remainder, complex retroperitoneal anastomoses were encountered.

CONCLUSION

By understanding these anatomic variations, the angiographer can approach treatment of right-sided varicocele with foreknowledge of the nature of these types and the presence of valves and collaterals.

Varicocele, hypoxia and male infertility. Fluid Mechanics analysis of the impaired testicular venous drainage system

BACKGROUND

Varicocele is a bilateral vascular disease, involving a network of collaterals and small, retroperitoneal bypasses. The right and the left testicular venous drainage systems are complex and not identical to each other. It was considered a predominantly unilateral (left-sided) disease. Its pathophysiology has not been clearly delineated and the treatments offered do not seem to be effective. The medical literature is replete with articles demonstrating inconsistent and even contradictory results which have led clinicians to dissociate varicocele from male infertility. Since male fertility is preserved with only one healthy testis, male infertility perforce represents bilateral testicular dysfunction. This poses an enigma to clinicians: How can left-sided varicocele causes bilateral testicular dysfunction?

METHODS

We investigated the internal spermatic veins by venography to understand testicular damage due to varicocele. A total of 740 venographies of the internal spermatic veins (ISVs) were performed, with sclerotherapy of the ISV as treatment for varicocele. Epon-embedded testicular tissue sections were used to identify blood stagnation in the testis.

RESULTS

Varicocele is predominantly a bilateral disease in 84% of cases, associated with collaterals and retroperitoneal venous bypasses in 70% in the left side and 75% in the right side. Histopathology demonstrate stagnation in the testicular microcirculation and hypoxic-ischaemic degenerative changes in all cells' types in the sperms' production site.

CONCLUSION

Based on our findings (i) varicocele is a bilateral disease; (ii) the disease is expressed earlier in the left side and is more intense because the blood column is longer in the left side than the right; (iii) partial treatment to the left side only and ignoring bypasses is not adequate to correct the problem; (iv) hypoxia leading to ischaemic damage to both testes is the effect of varicocele due to hydrostatic pressures in the impaired venous drainage system, which exceeds the pressures in the testicular arterial microcirculation due to blood columns produced in the disease; (v) hydrostatic pressure does not depend on vein diameter but on blood column height, only; and (vi) thermography alone or combined with ultrasonography with special attention to the bilaterality of the disease are the best non-invasive tools for its detection.

Uterine artery embolization: A pilot study in a rabbit model

Eight female adult ex-breeder New Zealand white rabbits underwent bilateral, unilateral, or superselective unilateral uterine artery embolization. The histopathologic changes after embolization in New Zealand white rabbits resemble those in humans, making rabbits an appropriate model for experimental uterine artery embolization.

Induction of spermatogenesis in azoospermic men after internal spermatic vein embolization for the treatment of varicocele

BACKGROUND

To evaluate the improvement in semen quality and pregnancy rate after internal spermatic vein (ISV) embolization in men with nonobstructive azoospermia virtual azoospermia, or extremely severe oligoteratoasthenoazoospermia (OTA).

METHODS

A prospective cohort of 101 azoospermic or severe oligoteratoasthenospermic men of mean (+/-SD) age 34.1+/-7.7 years who underwent ISV between September 1998 and June 2003 were evaluated for semen characteristics, endocrinology profile, and conception rate.

RESULTS

Significant improvement was noted in mean sperm concentration, motility, and morphology in 83 men (82%). Mean sperm concentration increased from 0.22+/-0.30 x 10(6)/ml total sperm in the ejaculate to 9.28+/-1.2 x 10(6)/ml after embolization (P < 0.001); mean sperm motility rose from 8.78+/-1.59 to 29.56+/-2.0% (P < 0.001), and mean sperm morphology rose from 3.79+/-0.74 to 13.72+/-1.37% (P < 0.005). Pregnancy was achieved in 34 cases (34%), 20 (20%) unassisted and 14 (14%) assisted.

CONCLUSIONS

Based on our findings, the following statements can be made: (i) Varicocele may cause any variation of severity in OTA, including azoospermia. (ii) Since male fertility is preserved with only one testis, OTA, azoospermia or virtual azoospermia represent bilateral testicular dysfunction. (iii) Treatment of bilateral varicocele may reverse testicular dysfunction and improve spermatognesis and testosterone production in men with extremely severe OTA and induce sperm production in men with azoospermia and virtual azoospermia. (iv) If azoospermia is not too long-standing, the treatment of varicocele may significantly improve spermatogenesis and renew sperm production. (v) Adequate treatment may spare in > 50% of azoospermic patients the need for testicular sperm extraction as preparation for ICSI. (vi) Since achievement of pregnancy in IVF units is higher when spermatogenesis is better, the treatment of varicocele (bilateral) is an effective medical adjunct for the IVF units prior to the treatment. We recommend that infertile men with azoospermia or virtual azoospermia or extremely severe OTA be evaluated for varicocele, with special attention to its bilateral nature.

Physical examination may miss the diagnosis of bilateral varicocele: a comparative study of 4 diagnostic modalities

PURPOSE

We evaluated the sensitivity of 3 noninvasive methods for detecting left and right varicoceles.

MATERIALS AND METHODS

Three noninvasive methods for the detection of varicocele in the left and right internal spermatic veins were evaluated in 214 infertile men, namely, physical examination, scrotal contact thermography and ultrasound Doppler. Venography was used as the reference diagnosis.

RESULTS

Varicocele was detected in 195 patients (91.1%), on the left side in 37 (19%), on the right side in 3 (1.5%) and bilaterally in 155 (79.5%). Scrotal contact thermography using varicoscreen proved to be the most accurate method. Sensitivity, specificity, accuracy and positive predictive value were 98.9%, 66.6%, 98.5% and 100%, respectively, for left varicocele, and 95.6%, 91.6%, 94.9% and 98%, respectively, for right varicocele. Doppler sonography was associated with the highest number of false-positive results. Accuracy in evaluating retrograde flow was lowest for both sides for physical examination and highest for the combination of Doppler sonography and contact thermography, with a sensitivity, specificity, accuracy and positive predictive value of 100%, 33.3%, 99.0% and 98.9%, respectively, for the left side, and 97.4%, 58.3%, 90.3% and 91.1%, respectively, for the right side. In 165 (85%) of the 195 patients who underwent internal spermatic vein embolization sperm parameters were improved.

CONCLUSIONS

The present study yielded 2 major findings. Thermography is more sensitive and accurate for the detection of varicocele than Doppler ultrasound and physical examination, and it can be used for screening as a single modality in infertile men. Doppler ultrasound and thermography are complementary and their combined use yields the highest sensitivity and accuracy.

Elevation of serum testosterone and free testosterone after embolization of the internal spermatic vein for the treatment of varicocele in infertile men

BACKGROUND

To evaluate the effect of internal spermatic vein (ISV) embolization on levels of serum testosterone and free testosterone and on spermatogenesis.

METHODS

The files of 83 infertile men treated for varicocele were reviewed for changes in serum testosterone, free testosterone and spermatogenesis after ISV embolization.

RESULTS

Mean serum testosterone concentration rose after embolization by 43%, from 12.07 +/- 6.07 nmol/l to 17.22 +/- 8.43 nmol/l (P<0.001). Mean serum free testosterone concentration rose by 72%, from 5.93 +/- 2.44 nmol/l to 10.21 +/- 7.69 nmol/l (P<0.001). Mean sperm concentration increased from 7.49 +/- 1.73 x 10(6)/ml to 18.14 +/- 2.36 x 10(6)/ml (P<0.001); mean sperm motility increased from 21.74 +/- 2.47 to 34.47 +/- 2.27% (P<0.001); and mean sperm morphology increased from 6.63 +/- 1.07 to 13.08 +/- 1.44% (P<0.001).

CONCLUSIONS

ISV embolization apparently induces an increase in both serum testosterone and free testosterone concentrations and in sperm parameters in infertile patient with varicocele, regardless of the size of the varicocele.

Varicocele: a bilateral disease

OBJECTIVE

To evaluate the prevalence of varicocele in the left and right spermatic veins in infertile men by several methods of examination.

DESIGN

Prospective study.

SETTING

Andrology unit of a department of obstetrics and gynecology, and interventional radiology unit of the radiology department at a tertiary care facility.

PATIENT(S)

Two hundred eighty-six infertile men evaluated for varicocele.

INTERVENTION(S)

Patients underwent evaluation for infertility. Physical examination was followed by contact thermography, Doppler sonography, and venography of both testes.

MAIN OUTCOME MEASURE(S)

We measured the prevalence of varicocele in the left and right spermatic veins in infertile men, and the response of semen parameters after embolization of internal spermatic vein.

RESULT(S)

Varicocele was detected by one of the noninvasive methods and confirmed by venography in 255 patients (89.2%): the left site in 45 (17.6%), the right side in 4 (1.5%), and bilaterally in 206 (80.8%). All patients were treated by embolization. Mean sperm concentration increased from 6.12 +/- 1.02 to 21.3 +/- 1.69 million/mL; mean sperm motility from 16.81 +/- 1.51 to 35.90 +/- 1.41%; and mean sperm morphology from 9.75 +/- 0.85 to 16.92 +/- 1.17%. Pregnancy rate was 43.5%.

CONCLUSION(S)

The present study finds that what was traditionally considered a predominantly unilateral anatomical abnormality apparently has a strikingly high bilateral prevalence (80.7%). This may suggest that we should consider varicocele a bilateral disease. The second finding is the high rate of varicocele detected by venography, thermography, and sonography when compared with physical examination results. Our study may have important implications for treatment, indicating that patients with clinical evidence of unilateral left varicocele should be carefully evaluated for bilateral varicocele.

Initial experience with ovarian vein embolization for the treatment of chronic pelvic pain syndrome

BACKGROUND

Ovarian vein embolization was recently suggested as the preferred treatment for chronic pelvic pain syndrome.

OBJECTIVE

To evaluate the technical feasibility, complications and early clinical and radiographic results of ovarian vein embolization in women with pelvic pain syndrome.

METHODS

Percutaneous transcatheter ovarian vein embolization with coils was performed in six patients aged 27-53 years who presented with pelvic pain syndrome. All had lower abdominal pain, and pelvic varicosities were found on Doppler ultrasound and retrograde ovarian vein venography. Embolization was done unilaterally in three patients (on the left side) and bilaterally in three. Mean follow-up by telephone questionnaire was 7.3 months.

RESULTS

The procedure was technically successful in all patients. Two patients reported partial relief of symptoms (33.3%) and three had complete relief (50%), for a total of 5 patients (83.3%) with some measure of improvement. There were no complications following the procedure.

CONCLUSIONS

Percutaneous transcatheter ovarian vein embolization seems to be safe and feasible for the treatment of pelvic pain syndrome. The procedure is performed on an outpatient basis and is well tolerated by patients.

Adolescent varicocele: is it a unilateral disease?

OBJECTIVES

To evaluate the incidence of left and right varicocele in adolescents.

METHODS

The study group consisted of 28 adolescents who underwent evaluation for varicocele at our clinic. In 19 patients, varicocele was detected on routine physical examination, and 9 patients presented with scrotal pain or discomfort. All patients were evaluated by three methods. Physical examination was followed in all cases by contact thermography and venography studies of both testes.

RESULTS

The rate of left and right retrograde flow in the spermatic veins by the three methods used was as follows: physical examination 92.8% and 10.7%; contact thermography 100% and 89%; and venography 100% and 85.7%, respectively. Varicocele was not detected by physical examination in 2 (7.2%) of the 28 patients on the left side and in 21 (87.5%) of 24 on the right side.

CONCLUSIONS

The main finding of this study was that varicocele is a bilateral disease in 85.7% of adolescents. The high percentage of bilateral varicocele in our sample may explain the pathophysiologic mechanism whereby what has traditionally been considered a unilateral disease can produce bilateral testicular dysfunction. The high incidence of subclinical bilateral varicocele may indicate that we should consider varicocele a bilateral disease. The second finding was that only 10% of patients with right varicocele were diagnosed by physical examination and more than 85% were diagnosed by thermography, with confirmation by venography. Therefore, we suggest that thermography and venography should play a major role in the diagnosis of varicocele.

Reading DNA differently

Product inhibition has provided the limiting barrier to efficient template-directed ligation and polymerization reactions. Here we review the attempts to circumvent this limitation and outline a translation strategy that does overcome the barrier and allows the information encoded in DNA to be read and amplified into backbone-modified oligonucleotides.

Effective light-induced hydroxylamine reactions occur with C13 = C14 nonisomerizable bacteriorhodopsin pigments

The light-driven proton pump bacteriorhodopsin (bR) undergoes a bleaching reaction with hydroxylamine in the dark, which is markedly catalyzed by light. The reaction involves cleavage of the (protonated) Schiff base bond, which links the retinyl chromophore to the protein. The catalytic light effect is currently attributed to the conformational changes associated with the photocycle of all-trans bR, which is responsible for its proton pump mechanism and is initiated by the all-trans --> 13-cis isomerization. This hypothesis is now being tested in a series of experiments, at various temperatures, using three artificial bR molecules in which the essential C13==C14 bond is locked by a rigid ring structure into an all-trans or 13-cis configuration. In all three cases we observe an enhancement of the reaction by light despite the fact that, because of locking of the C13==C14 bond, these molecules do not exhibit a photocycle, or any proton-pump activity. An analysis of the rate parameters excludes the possibility that the light-catalyzed reaction takes place during the approximately 20-ps excited state lifetimes of the locked pigments. It is concluded that the reaction is associated with a relatively long-lived (micros-ms) light-induced conformational change that is not reflected by changes in the optical spectrum of the retinyl chromophore. It is plausible that analogous changes (coupled to those of the photocycle) are also operative in the cases of native bR and visual pigments. These conclusions are discussed in view of the light-induced conformational changes recently detected in native and artificial bR with an atomic force sensor.

Microsecond atomic force sensing of protein conformational dynamics: implications for the primary light-induced events in bacteriorhodopsin

In this paper a new atomic force sensing technique is presented for dynamically probing conformational changes in proteins. The method is applied to the light-induced changes in the membrane-bound proton pump bacteriorhodopsin (bR). The microsecond time-resolution of the method, as presently implemented, covers many of the intermediates of the bR photocycle which is well characterized by spectroscopical methods. In addition to the native pigment, we have studied bR proteins substituted with chemically modified retinal chromophores. These synthetic chromophores were designed to restrict their ability to isomerize, while maintaining the basic characteristic of a large light-induced charge redistribution in the vertically excited Franck-Condon state. An analysis of the atomic force sensing signals lead us to conclude that protein conformational changes in bR can be initiated as a result of a light-triggered redistribution of electronic charge in the retinal chromophore, even when isomerization cannot take place. Although the coupling mechanism of such changes to the light-induced proton pump is still not established, our data question the current working hypothesis which attributes all primary events in retinal proteins to an initial trans<==>cis isomerization.

[Seminiferous tubule cytological pattern in infertile, azoospermic men in diagnosis and therapy]

We determined spermatogenic patterns of seminiferous tubules in azoospermic infertile men and evaluated the prevalence of bilateral testicular homogeneity. 185 azoospermic men underwent bilateral testicular fine-needle aspiration (TFNA) in which each testis was punctured at 3 different positions. Aspirated material was stained and classified according to the most mature spermatogenic cell type present or whether only Sertoli cells were present. 35.7% had spermatozoa in their testes, 36.2% had spermatogenic maturation arrest, and 28.1% had only Sertoli cells in their seminiferous tubules. In 15.6% of all patients, the diagnosis in 1 testis differed from that in the other. In only 73.2% of those with testicular spermatozoa was it bilateral. In the remaining 26.9%, only Sertoli cells, spermatocytes or spermatids were found as the most mature cell type in the other testis. The study definitely indicates that fertilization with retrieved testicular spermatozoa should not be offered to azoospermic patients without prior evaluation of the seminiferous tubuespermatogenic pattern in both testes.

Interaction between Asp-85 and the proton-releasing group in bacteriorhodopsin. A study of an O-like photocycle intermediate

Upon light adaptation by continuous (or pulsed) illumination, the artificial bacteriorhodopsin (bR) pigments, I and II, derived from synthetic 14F retinal and a short polyenal, respectively produce a long-lived red-shifted species denoted O1. An analogous phenomenon was observed by Sonar, S., et al. [(1993) Biochemistry 32, 2263-2271], in the case of the Y185F mutant (pigment III). The nature of these O1 species was investigated by studying a series of effects, primarily their red light photoreversibility, the associated proton uptake and release processes, and the effects of pH on their relative amounts, which are interpreted in terms of pH-dependent acid-base equilibria. Experiments were also carried out with pigments I and II derived from the mutants D96A, E204Q, R82Q, and D85N. The O1 species of pigments I and II (and possibly also that of pigment III) are identified as an unusually long-lived (all-trans) intermediate of the photocycle of their 13-cis isomer. It is concluded that in O1, Asp-85 is protonated, a process associated with proton uptake from the extracellular side. Subsequent proton release (to the same side of the membrane) occurs from Glu-204 (or from a group closely interacting with it) prior to the decay of O1. At high pH (>9), O1 reversibly converts to a purple form, due to deprotonation of Asp-85, while at still higher pH (> 11), a blue-shifted species characterized by a deprotonated Schiff base is generated. These transitions constitute the first demonstration of the titration of a photocycle intermediate of a retinal protein. The respective pKa values are determined and discussed in relation to those pertaining to the unphotolyzed (dark-adapted) pigments. It appears that the pKa values are controlled by a hydrogen bond network involving water molecules, which binds the protonated Schiff base with Asp-85 and Glu-204. The disruption of this network in pigments I-III may also be responsible for the long lifetime of the O1 species, due to the inhibition of thermal trans-13-cis isomerization. The results are relevant to the molecular mechanism of the photocycles of both 13-cis- and all-trans-bR, primarily to the nature and to the deprotonation mechanism of the proton-releasing group.

On the heterogeneity of the M population in the photocycle of bacteriorhodopsin

The M stage in the photocycle of bacteriorhodopsin (bR), a key step in its light-induced proton pump mechanism, is studied in water/glycerol suspensions over the temperature range between 20 and -60 degrees C. The biexponential decay of M is analyzed for wild-type (WT) bR and for its D96N, Y185F, and D115N mutants, at various pH values, according to the scheme: bR-->(hv) L-->M<-->(k1, k-1) N-->(k2) bR. The analysis leads to the conclusion that the N state is generated, with analogous rate parameters, in all cases, including the D96N mutant. Another approach involves probing the M state, generated by steady-state illumination at -60 degrees C, by fast cooling to -180 degrees C. Subsequent irradiation with blue light, followed by gradual warming up, induces the M-->(hv) M'-->bR'-->bR sequence of reactions. On the basis of characteristic difference spectra and transition temperatures observed for the M'-->bR' process, it is concluded that the initially observed M state at -60 degrees C, denoted as (M)a, is composed of three (or four) equilibrated substrates, MI, MII, MIII, and MIV. During the M-->N equilibration, which corresponds to the fast phase of the M decay, (M)a transforms into a second state, (M)b, in which MIII has been replaced by a fifth M substate, denoted as MV. MV is identified as the protein state in which an appropriate structural change allows reprotonation of the Schiff base, generating the N state. The low-temperature heterogeneity in M is discussed in terms of the two M states (M1 and M2) previously postulated [Váró, G., & Lanyi, J. K. (1990) Biochemistry 29, 2241] for the room temperature photocycle. The following conclusions are derived for both low and room temperature photocycles: (a) The M population is highly heterogeneous and pH dependent. (b) At least three transitions are observed between the initially formed M state and the M state that is equilibrated with N. These are assigned to protein conformational changes and to water molecule rearrangements. (c) In an aqueous suspension of WT bR at room temperature, the Schiff base reprotonation is controlled by D96. However, our results show that the formation and stability of the N state do not require the D96 residue. Moreover, at low temperatures, the (M)a-->(M)b protein structural transformation, which has not yet been resolved at room temperature, becomes the rate-determining step in the protonation of the Schiff base.

The retinal Schiff base-counterion complex of bacteriorhodopsin: changed geometry during the photocycle is a cause of proton transfer to aspartate 85

Bacteriorhodopsin contains all-trans-retinal linked via a protonated Schiff base to K216. The proton transport in this pump is initiated by all-trans to 13-cis photoisomerization of the retinal and the ensuing transfer of the Schiff base proton to D85. Changed geometrical relationship of the Schiff base and D85 after the photoisomerization is a possible reason for the proton transfer. We introduced small volume/shape changes with site-specific mutagenesis of residues V49 and A53 that contact the side chain of K216, in order to force the Schiff base into somewhat different positions relative to D85. Earlier [Zimányi, L., Váró, G., Chang, M., Ni, B., Needleman, R., & Lanyi, J. K. (1992) Biochemistry 31, 8535-8543] we had described the kinetics of absorbance changes in the microsecond to millisecond time range after photoexcitation with the scheme L<-->M1<-->M2 + H+ (where the first equilibrium is the internal proton transfer and the second is proton release on the extracellular surface). Testing it at various pH values with mutants, where selected rate constants are changed, now confirms the validity of this scheme. The kinetics of the M state thus allowed examination of the transient equilibrium that develops in the L<-->M1 reaction and represents the redistribution of the proton between the Schiff base and D85. From the structure of the protein, the V49A and V49M residue replacements were both predicted to cause decreased alignment of the Schiff base and D85, and indeed we found that they both changed the equilibrium toward the protonated Schiff base. In contrast, the residue replacements A53V and A53G were predicted to move the Schiff base in opposite directions, away from and closer to alignment with D85, respectively. The former indeed changed the equilibrium toward the protonated Schiff base and the latter toward the deprotonated Schiff base. In addition, the hydroxyl stretch band of a bound water in the L state was affected by all mutations that disfavor proton transfer to D85. We conclude that the geometry of the proton donor and acceptor in the Schiff base-D85 pair, mediated by bound water, is a determinant of the proton transfer equilibrium.

Active site lysine backbone undergoes conformational changes in the bacteriorhodopsin photocycle

Results are presented demonstrating that the backbone of the active site lysine of bacteriorhodopsin undergoes light-induced structural alterations during bacteriorhodopsin-mediated light-induced proton pumping. This conclusion is based on difference Fourier transform infrared spectroscopy of isotopically labeled bacteriorhodopsin. The data demonstrate that the backbone carbonyl of lysine achieves an extremely low vibrational frequency during M412 intermediate formation. This is preceded by a structural transition in the lysine backbone that leads to an active site lysine carbonyl with the observed low vibrational frequency, probably due to a high degree of solvation.

Participation of bacteriorhodopsin active-site lysine backbone in vibrations associated with retinal photochemistry

Bacteriorhodopsin (bR) has been biosynthetically prepared with lysine deuterated at its alpha carbon (C alpha--H). The labeled membranes containing bR were investigated by difference Fourier transform infrared (FTIR) spectroscopy. It has been derived from K/bR and M/bR difference spectra (K and M are photocycle intermediates) that several bands previously assigned to the retinal chromophore are coupled to the C alpha--H. The vibrational modes that exhibit this coupling are principally associated with C15--H and N--H vibrations. [C alpha--2H]Lysine-labeled bR was fragmented enzymatically, and bR structures were regenerated with the C alpha--2H label either on lysine-216 and -172 or on the remaining five lysine residues of the protein. FTIR studies of the regenerated bR system, together with methylation of all lysines except the active-site lysine, reveal that the changes observed due to backbone labeling arise from the active-site lysine. The intensity of the C15--H out-of-plane wag is interpreted as a possible indication of a twist around the C15 = N bond.