Structures of Invertebrate Hemoglobins

Hemoglobin is widely distributed among the invertebrates. Intracellularhemoglobins consist of relatively small molecules with mol wtsof 15–17,000 or dimeric, tetrameric or octameric aggregatesof 15–17,000 mol wt subunits. Sequence homology is presentbut not extensive in those pigments which have been studiedand the characteristic myoglobin fold of vertebrate hemoglobinoccurs in at least two invertebrate hemoglobins. The wide arrayof aggregation states among invertebrate hemoglobins providessome simple models for understanding homotropic functional propertiesexhibited by many of these pigments. Polymeric extracellularhemoglobins are present in annelids molluscs crustacean arthropodsand nematodes. Annelid extracellular hemoglobins and chlorocruorinsconsist of 3 x 10⁶ mol wt two-tiered hexagonal arrays of submultipleswhich in turn are based on polypeptide chain subunits of molwt 14–16 000. Molluscan extracellular hemoglobins areconstructed from a different subunit arrangement. In the planorbidsnail and clam extracellular hemoglobins the subunits appearto be 175 000 and 300 000 mol wt linear series of 15–17000 dalton oxygen binding domains respectively. Planorbid snailnative hemoglobin presents circular structures 200 Å indiameter in the electron microscope with 10-fold symmetry inat least one view, and clam extracellular hemoglobins are huge345 by 1200 Å rodlike structures. Crustacean extracellularhemoglobins are also polymeric pigments and at least in a fewspecies appear to have subunits which are tandemly linked oxygenbinding domains. The polymeric hemoglobins of nematodes havemolecular weights of about 330 000. The subunit molecular weightand heme content suggest a value of 40,000 daltons which setthe nematode pigments apart from all other hemoglobins so farstudied. An overview of invertebrate hemoglobin structures andsome of the questions they pose are presented in this paper.     

Fruiting in Sphaerobolus with Special Reference to Light

Sphaerobolus grows and, provided there is sufficient illumination,fruits readily on oatmeal agar or on malt agar. No effect oflight on vegetative growth can be demonstrated. On the maltmedium, increased fruiting occurs with increase of nutrientup to 4 per cent, malt, but at higher concentrations fruitingis not increased and may be retarded. A chemically defined mediumwith starch as the carbon source allows fruiting, but at a lowlevel. Temperature has a profound effect on basidiocarp development;above 25 C. no fruit-bodies are normally formed although vegetativegrowth is approximately optimal at that temperature. For overallfruit-body production at 20 C, light above 100 lux is necessaryand light remains a limiting factor up to about 1, 000 lux.Under continuous light of suitable intensity, fruit-bodies continueto develop and discharge glebal-masses for many weeks. Thereis a distinct periodicity of discharge with (at 20 C.) about12 days between peaks of activity. This corresponds with thetime taken for basidiocarp initiation and development. A number of developmental stages of the basidiocarp are recognized.The final stage, glebal-mass discharge from stellately openedfruit-bodies, is indifferent to light, but all other stagesare stimulated by light. The light intensity for effective stimulationfalls during development and for the penultimate stage an intensityas low as 1 lux is effective. Only light of wave-length below500 mµ is active in overall basidiocarp development. Inthe sensitive region between 400 mµ and 500 mµ,there appear to be peaks of sensitivity around 440 mµand 480 mµ. In alternating light and darkness, simulating natural conditions,glebal-mass discharge occurs in the light periods. With a regimenof 24 hours light and 24 hours of darkness discharge is mainlyin the dark periods.     

Sporophore Production in Sphaerobolus with Special Reference to Periodicity

Further observations on temperature and fruiting are reported.The minimum and optimum values depend on the time when observationsare made. The effect on discharge from sporulating culturesof illumination interrupted by dark periods (i-ii days) is considered.If the dark period does not exceed a day, harge recommenceson the second and subsequent days of renewed illumina if itis 2–4 days, discharge occurs on the second day afterreturn to light but not thereafter; if the period of darknessexceeds 5 days, discharge does not mmence on subsequent illuminationuntil a completely new crop of sporophores is formed. Experiments are reported in which it is shown that at 20°C there is an interval of about I day between the onset of adark period and the inhibition of discharge related to it. Thisperiod is increased to a day and a half at 10° C. At thistemper an alternation of roughly equal light and dark periodseach day leads to dis in the dark periods and not in the lightperiods as at 20° C. Experiments are reported which support the view that the long-termof discharge in cultures under constant conditions relates toinhibition of development of primordia by maturing sporophores.