Adsorption chromatography of cyclic nucleotides on silica gel and alumina thin-layer sheets

FSH and testosterone effects in seminiferous tubules of immature hypophysectomized rats

The effects of follicle-stimulating hormone (FSH) and testosterone on the development of the cytosolic germ cell adenylate cyclase and germ cell morphology in rats hypophysectomized at 29 days of age were studied. Following hypophysectomy, the adenylate cyclase content fell to marginal levels and germ cell development ceased at the late pachytene stage. Testosterone treatment led to a moderate increase in the cytosolic enzyme content and to progression of spermatid cell development to stages 8-12. FSH treatment with doses of 80-100 micrograms/day restored enzyme content to levels seen in control rats, as well as progression of germ cell development up to stages 15-16, i.e., to the same stages present in age-matched control (sham-operated) rats. The results indicate that in immature rats FSH is essential for spermatid cell maturation as is evidenced by its ability to stimulate the formation of cytosolic germ cell adenylate cyclase to quantitatively normal levels, as well as to stimulate the development of spermatid cells.

A calcium/calmodulin-dependent cyclic adenosine monophosphate phosphodiesterase from Drosophila heads

A Ca2+-activated cycl AMP phosphodiesterase from Drosophila melanogaster heads was studied. The enzyme accounted for approx. 40% of the total, soluble cyclic AMP phosphodiesterase activity in heads. After gel filtration, Ca2+ stimulation of the enzyme was no longer apparent, but Ca2+ activation could be restored by the addition of boiled Drosophila extract to the column-fractionated phosphodiesterase. The protein responsible for restoring Ca2+ activation was purified and shown to have some characteristics of calmodulin. In addition, porcine calmodulin was able to activate the Drosophila phosphodiesterase. Thus, the phosphodiesterase-calmodulin system in Drosophila appears analogous to similar systems in mammals.

Regulation of the microtubule steady state in vitro by ATP

ATP increases microtubule steady state assembly and disassembly rates in vitro in a concentration-dependent manner. Bovine brain microtubules, composed of 75% tubulin and 25% high molecular weight microtubule-associated proteins (MAPs), were purified by three cycles of assembly and disassembly in the absence of ATP. When assembled to steady state, these microtubules add dimers at one end and lose them at the other in a unidirectional assembly-disassembly process. In the presence of 1.0 mM ATP the unidirectional flow of tubulin from one end of the microtubules to the other increases as much as 20 fold, as revealed by loss of 3H-GTP from uniformly labeled microtubules under GTP chase conditions and by the rate of disassembly following addition of 50 microM podophyllotoxin. UTP, CTP and 5' adenylylimidodiphosphate (AMP-PNP) cannot substitute for ATP in producing this effect. Furthermore, the increase in steady state flow rate persists afer ATP is removed. Thus microtubules assembled in ATP and centrifuged through sucrose cushions to separate them from nucleotides continue to exhibit increased rates in the next assembly cycle in the absence of ATP. It is possible that an ATP-dependent microtubule protein kinase is responsible for the observed increase in tubulin flow rate. A kinase activity associated with brain MAPs has been reported to be cAMP-dependent (Sloboda et al., 1975). We have found an adenylate cyclase activity associated with these microtubules. Whether the adenylate cyclase is a contaminant or due to a specific microtubules-associated protein, and whether its activity is functionally linked to the increased rate of assembly and disassembly in the presence of ATP, remain to be determined.

Separation of cyclic AMP and cyclic GMP from thymidine, electrolytes and polyvalent nucleotides in tissue samples

Cyclic AMP and cyclic GMP can be separated from thymidine and its possible metabolites, electrolytes, and polyvalent nucleotides using columns of acidic alumina. Electrolytes and thymidine are not adsorbed on acidic alumina at pH 4.4 while cyclic nucleotides and polyvalent nucleotides are adsorbed at this pH. Cyclic AMP and cyclic GMP are eluted together from acidic alumina with 0.2 M ammonium formate (pH 6.0) and the polyvalent nucleotides remain adsorbed. The cyclic nucleotides are separated by chromatography on Dowex AG 1 X 8 resin. Recovery is 60--64% for cyclic AMP and cyclic GMP isolated from renal tissue samples. This methodology permits the separation of tritiated thymidine from cyclic nucleotides which are present in tissue preparations used in studies on the role of cyclic nucleotides in cellular growth.

Mn2+-sensitive, soluble adenylate cyclase in rat testis. Differentiation from other testicular nucleotide cyclases

In subcellular fractions prepared from homogenate of adult rat testis adenylate cyclase (ATP pyrophosphate-lyase (cyclizing), EC 4.6.1.1) activity was found in the particulate, primarily 600 X g for 10 min, fractions, as well as in the cytosol. The properties of the adenylate cyclase in the cytosol differs substantially from the adenylate cyclase system associated with the 600 X g for 10 min particulate fraction. The cytosol enzyme, in contrast to the particulate adenylate cyclase, was found to be fluoride- and gonadotropin hormone-insensitive. The cytosol adenylate cyclase appears to be located in the germ cell while the particulate enzyme system in the non-germ cell component of the seminiferous tubules, The cytosol adenylate cyclase was found to be distinct also from the guanylate cyclase present in the rat testis cytosol. The adenylate cyclase appears to be located in the germ cell component while the guanylate cyclase, in the non-germ cell tubular component. Furthermore, it was found that the cytosol guanylate cyclase develops at an earlier stage of spermatogenesis, and precedes the development of the cytosol adenylate cyclase.

LH- and FSH-stimulating of adenylate cyclase in seminiferous tubules from young rats: functional FSH and LH receptors unmasked by homogenization

LH- and FSH-sensitive adenylate cyclase activity was present in homogenates of whole testis tissue as well as in microdissected seminiferous tubules derived from young rats. In homogenates of seminiferous tubules a single adenylate cyclase appears to interact with both LH and FSH through separate hormone-specific receptors. Disruption of testis tissue by homogenization exposes functional FSH and LH receptors which are inaccessible to the hormones in intact cell preparations. These results indicate that in certain seminiferous tubule cell types only a fraction of the total functional receptors present is accessible to the cell surface for interaction with hormone.

Development of a Mn-2+-sensitive, "soluble" adenylate cyclase in rat testis

A distinctive Mn-2+-sensitive adenylate cyclase [ATP pyrophosphate-lyase(cyclizing), EC 4.6.1.1] system insensitive to fluoride has been found in rat seminiferous tubules and epididymal sperm. The development of this distinctive adenylate cyclase in testis was studied during spermatogenesis. It was first detectable in seminiferous tubules in immature rats at about the time of the first reductive divisions and the appearance of spermatid cells. The specific activity of the enzyme increased substantially during the period of spermatogenesis when spermatids develop into mature spermatozoa, and reached maximal values in the testis of adult rats. After centrifugation of testis tissue homogenates at 105,000 X g for 60 min, the Mn-2+-sensitive adenylate cyclase activity was found in the cytosol. The enzyme remains in solution after centrifugation at 300,000 X g for 5 hr or at 180,000 X g for 24 hr and passes through a 0.22 mum Millipore filter. Electron microscopic examination showed no visible membrane fragments or vesicles in the filtered supernatant. The Mn-2+-sensitive adenylate cyclase system is also present in epidiymal sperm. However, in the sperm obtained from either the caput or the cauda of epididymis, the adenylate cyclase is membrane-associated and found in particulate fractions of sperm homogenates. It therefore appears that the Mn-2+-sensitive adenylate cyclase is initially present in the cytoplasm either unattached or loosely bound to intracellular membranes and becomes firmly attached to sperm membranes later in development. This occurs either during the process of maturation of spermatids into sperm or during the transport of the testicular sperm into the epididymis.